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Chapter 3 The Thorax: Part II—The Thoracic Cavity A 54-year-old woman complaining of a sudden excruciating knifelike pain in the front of the chest was seen by a physician. During the course of the examination, she said that she could also feel the pain in her back between the shoulder blades. On close questioning she said she felt no pain down the arms or in the neck. Her blood pressure was 200/110 mm Hg in the right arm and 120/80 mm Hg in the left arm. The evaluation of chest pain is one of the most common problems facing an emergency physician. The cause can vary from the simple to one of life-threatening proportions. The severe nature of the pain and its radiation through to the back made a preliminary diagnosis of aortic dissection a strong possibility. Myocardial infarction commonly results in referred pain down the inner side of the arm or up into the neck. Pain impulses originating in a diseased descending thoracic aorta pass to the central nervous system along sympathetic nerves and are then referred along the somatic spinal nerves to the skin of the anterior and posterior chest walls. In this patient the aortic dissection had partially blocked the origin of the left subclavian artery, which would explain the lower blood pressure recorded in the left arm. Chapter Objectives

  • To understand the general arrangement of the thoracic viscera and their relationship to one another and to the chest wall.
  • To be able to define what is meant by the term mediastinum and to learn the arrangement of the pleura relative to the lungs. This information is fundamental to the comprehension of the function and disease of the lungs.
  • Appreciating that the heart and the lungs are enveloped in serous membranes that provide a lubricating mechanism for these mobile viscera and being able to distinguish between such terms as thoracic cavity, pleural cavity (pleural space), pericardial cavity, and costodiaphragmatic recess.
  • To learn the structure of the heart, including its conducting system and the arrangement of the different chambers and valves, which is basic to understanding the physiologic and pathologic features of the heart. The critical nature of the blood supply to the heart and the end arteries and myocardial infarction is emphasized.
  • To understand that the largest blood vessels in the body are located within the thoracic cavity, namely, the aorta, the pulmonary arteries, the venae cavae, and the pulmonary veins. Trauma to the chest wall can result in disruption of these vessels, with consequent rapid hemorrhage and death. Because these vessels are hidden from view within the thorax, the diagnosis of major blood vessel injury is often delayed, with disastrous consequences to the patient.

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Basic Anatomy Chest Cavity The chest cavity is bounded by the chest wall and below by the diaphragm. It extends upward into the root of the neck about one fingerbreadth above the clavicle on each side (see Fig. 3-5). The diaphragm, which is a very thin muscle, is the only structure (apart from the pleura and peritoneum) that separates the chest from the abdominal viscera. The chest cavity can be divided into a median partition, called the mediastinum, and the laterally placed pleurae and lungs (Figs. 3-1, 3-2, and 3-3). P.79

Figure 3-1 Cross section of the thorax at the level of the eighth thoracic vertebra. Note the arrangement of the pleura and pleural cavity (space) and the fibrous and serous pericardia.
Figure 3-2 Subdivisions of the mediastinum.

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Figure 3-3 Pleurae from above and in front. Note the position of the mediastinum and hilum of each lung.

Mediastinum The mediastinum, though thick, is a movable partition that extends superiorly to the thoracic outlet and the root of the neck and inferiorly to the diaphragm. It extends anteriorly to the sternum and posteriorly to the vertebral column. It contains the remains of the thymus, the heart and large blood vessels, the trachea and esophagus, the thoracic duct and lymph nodes, the vagus and phrenic nerves, and the sympathetic trunks. The mediastinum is divided into superior and inferior mediastina by an imaginary plane passing from the sternal angle anteriorly to the lower border of the body of the fourth thoracic vertebra posteriorly (Fig. 3-2). The inferior mediastinum is further subdivided into the middle mediastinum, which consists of the pericardium and heart; the anterior mediastinum, which is a space between the pericardium and the sternum; and the posterior mediastinum, which lies between the pericardium and the vertebral column. For purposes of orientation, it is convenient to remember that the major mediastinal structures are arranged in the following order from anterior to posterior. Superior Mediastinum (a) Thymus, (b) large veins, (c) large arteries, (d) trachea, (e) esophagus and thoracic duct, and (f) sympathetic trunks The superior mediastinum is bounded in front by the manubrium sterni and behind by the first four thoracic vertebrae (Fig. 3-2). Inferior Mediastinum (a) Thymus, (b) heart within the pericardium with the phrenic nerves on each side, (c) esophagus and thoracic duct, (d) descending aorta, and (e) sympathetic trunks The inferior mediastinum is bounded in front by the body of the sternum and behind by the lower eight thoracic vertebrae (Fig. 3-2). Pleurae The pleurae and lungs lie on either side of the mediastinum within the chest cavity (Fig. 3-3). Before discussing the pleurae, it might be helpful to look at the illustrations of the development of the lungs in Figure 3-4. P.81

Figure 3-4 Formation of the lungs. Note that each lung bud invaginates the wall of the coelomic cavity and then grows to fill a greater part of the cavity. Note also that the lung is covered with visceral pleura and the thoracic wall is lined with parietal pleura. The original coelomic cavity is reduced to a slitlike space called the pleural cavity as a result of the growth of the lung.

Clinical Notes Deflection of Mediastinum In the cadaver, the mediastinum, as the result of the hardening effect of the preserving fluids, is an inflexible, fixed structure. In the living, it is very mobile; the lungs, heart, and large arteries are in rhythmic pulsation, and the esophagus distends as each bolus of food passes through it. If air enters the pleural cavity (a condition called pneumothorax), the lung on that side immediately collapses and the mediastinum is displaced to the opposite side. This condition reveals itself by the patient’s being breathless and in a state of shock; on examination, the trachea and the heart are found to be displaced to the opposite side. Mediastinitis The structures that make up the mediastinum are embedded in loose connective tissue that is continuous with that of the root of the neck. Thus, it is possible for a deep infection of the neck to spread readily into the thorax, producing a mediastinitis. Penetrating wounds of the chest involving the esophagus may produce a mediastinitis. In esophageal perforations, air escapes into the connective tissue spaces and ascends beneath the fascia to the root of the neck, producing subcutaneous emphysema. Mediastinal Tumors or Cysts Because many vital structures are crowded together within the mediastinum, their functions can be interfered with by an enlarging tumor or organ. A tumor of the left lung can rapidly spread to involve the mediastinal lymph nodes, which on enlargement may compress the left recurrent laryngeal nerve, producing paralysis of the left vocal fold. An expanding cyst or tumor can partially occlude the superior vena cava, causing severe congestion of the veins of the upper part of the body. Other pressure effects can be seen on the sympathetic trunks, phrenic nerves, and sometimes the trachea, main bronchi, and esophagus. Mediastinoscopy Mediastinoscopy is a diagnostic procedure whereby specimens of tracheobronchial lymph nodes are obtained without opening the pleural cavities. A small incision is made in the midline in the neck just above the suprasternal notch, and the superior mediastinum is explored down to the region of the bifurcation of the trachea. The procedure can be used to determine the diagnosis and degree of spread of carcinoma of the bronchus.

Figure 3-5 Different areas of the parietal pleura. Note the cuff of pleura (dotted lines) that surrounds structures entering and leaving the hilum of the left lung. It is here that the parietal and visceral layers of pleura become continuous. Arrows indicate the position of the costodiaphragmatic recess.

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Each pleura has two parts: a parietal layer, which lines the thoracic wall, covers the thoracic surface of the diaphragm and the lateral aspect of the mediastinum, and extends into the root of the neck to line the undersurface of the suprapleural membrane at the thoracic outlet; and a visceral layer, which completely covers the outer surfaces of the lungs and extends into the depths of the interlobar fissures (Figs. 3-1, 3-3, 3-4, 3-5, and 3-6). The two layers become continuous with one another by means of a cuff of pleura that surrounds the structures entering and leaving the lung at the hilum of each lung (Figs. 3-3, 3-4, and 3-5). To allow for movement of the pulmonary vessels and large bronchi during respiration, the pleural cuff hangs down as a loose fold called the pulmonary ligament (Fig. 3-5).

Figure 3-6 Cross section of the thorax. A. At the inlet, as seen from above. B. At the fourth thoracic vertebra, as seen from below.

The parietal and visceral layers of pleura are separated from one another by a slitlike space, the pleural cavity (Figs. 3-3 and 3-4). (Clinicians are increasingly using the term pleural space instead of the anatomic term pleural cavity. This is probably to avoid the confusion between P.84
the pleural cavity [slitlike] space and the larger chest cavity.) The pleural cavity normally contains a small amount of tissue fluid, the pleural fluid, which covers the surfaces of the pleura as a thin film and permits the two layers to move on each other with the minimum of friction.

Figure 3-7 Lateral view of the upper opening of the thoracic cage showing how the apex of the lung projects superiorly into the root of the neck. Note that the lung apex is covered with visceral and parietal layers of pleura and is protected by the suprapleural membrane.

For purposes of description, it is customary to divide the parietal pleura according to the region in which it lies or the surface that it covers. The cervical pleura extends up into the neck, lining the undersurface of the suprapleural membrane (Fig. 3-7). It reaches a level 1 to 1.5 in. (2.5 to 4 cm) above the medial third of the clavicle. The costal pleura lines the inner surfaces of the ribs, the costal cartilages, the intercostal spaces, the sides of the vertebral bodies, and the back of the sternum (Fig. 3-3). The diaphragmatic pleura covers the thoracic surface of the diaphragm (Figs. 3-3 and 3-5). In quiet respiration, the costal and diaphragmatic pleurae are in apposition to each other below the lower border of the lung. In deep inspiration, the margins of the base of the lung descend, and the costal and diaphragmatic pleurae separate. This lower area of the pleural cavity into which the lung expands on inspiration is referred to as the costodiaphragmatic recess (Figs. 3-4 and 3-5). The mediastinal pleura covers and forms the lateral boundary of the mediastinum (Figs. 3-3 and 3-5). At the hilum of the lung, it is reflected as a cuff around the vessels and bronchi and here becomes continuous with the visceral pleura. It is thus seen that each lung lies free except at its hilum, where it is attached to the blood vessels and bronchi that constitute the lung root. During full inspiration the lungs expand and fill the pleural cavities. However, during quiet inspiration the lungs do not fully occupy the pleural cavities at four sites: the right and left costodiaphragmatic recesses and the right and left costomediastinal recesses. The costodiaphragmatic recesses are slitlike spaces between the costal and diaphragmatic parietal pleurae that are separated only by a capillary layer of pleural fluid. During inspiration, the lower margins of the lungs descend into the recesses. During expiration, the lower margins of the lungs ascend so that the costal and diaphragmatic pleurae come together again. The costomediastinal recesses are situated along the anterior margins of the pleura. They are slitlike spaces between the costal and the mediastinal parietal pleurae, which are separated by a capillary layer of pleural fluid. During inspiration and expiration, the anterior borders of the lungs slide in and out of the recesses. The surface markings of the lungs and pleurae were described on pages 68 and 72. Nerve Supply of the Pleura The parietal pleura (Fig. 3-8) is sensitive to pain, temperature, touch, and pressure and is supplied as follows:

  • The costal pleura is segmentally supplied by the intercostal nerves.
  • The mediastinal pleura is supplied by the phrenic nerve.
  • The diaphragmatic pleura is supplied over the domes by the phrenic nerve and around the periphery by the lower six intercostal nerves.

The visceral pleura covering the lungs is sensitive to stretch but is insensitive to common sensations such as pain and touch. It receives an autonomic nerve supply from the pulmonary plexus (Fig. 3-8). P.85

Figure 3-8 Diagram showing the innervation of the parietal and visceral layers of pleura.

Clinical Notes Pleural Fluid The pleural space normally contains 5 to 10 mL of clear fluid, which lubricates the apposing surfaces of the visceral and parietal pleurae during respiratory movements. The formation of the fluid results from hydrostatic and osmotic pressures. Since the hydrostatic pressures are greater in the capillaries of the parietal pleura than in the capillaries of the visceral pleura (pulmonary circulation), the pleural fluid is normally absorbed into the capillaries of the visceral pleura. Any condition that increases the production of the fluid (e.g., inflammation, malignancy, congestive heart disease) or impairs the drainage of the fluid (e.g., collapsed lung) results in the abnormal accumulation of fluid, called a pleural effusion. The presence of 300 mL of fluid in the costodiaphragmatic recess in an adult is sufficient to enable its clinical detection. The clinical signs include decreased lung expansion on the side of the effusion, with decreased breath sounds and dullness on percussion over the effusion. Pleurisy Inflammation of the pleura (pleuritis or pleurisy), secondary to inflammation of the lung (e.g., pneumonia), results in the pleural surfaces becoming coated with inflammatory exudate, causing the surfaces to be roughened. This roughening produces friction, and a pleural rub can be heard with the stethoscope on inspiration and expiration. Often the exudate becomes invaded by fibroblasts, which lay down collagen and bind the visceral pleura to the parietal pleura, forming pleural adhesions. Pneumothorax, Empyema, and Pleural Effusion As the result of disease or injury (stab or gunshot wounds), air can enter the pleural cavity from the lungs or through the chest wall (pneumothorax). In the old treatment of tuberculosis, air was purposely injected into the pleural cavity to collapse and rest the lung. This was known as artificial pneumothorax. A spontaneous pneumothorax is a condition in which air enters the pleural cavity suddenly without its cause being immediately apparent. After investigation, it is usually found that air has entered from a diseased lung and a bulla (bleb) has ruptured. Stab wounds of the thoracic wall may pierce the parietal pleura so that the pleural cavity is open to the outside air. This condition is called open pneumothorax. Each time the patient inspires, it is possible to hear air under atmospheric pressure being sucked into the pleural cavity. Sometimes the clothing and the layers of the thoracic wall combine to form a valve so that air enters on inspiration but cannot exit through the wound. In these circumstances, the air pressure builds up on the wounded side and pushes the mediastinum toward the opposite side. In this situation, a collapsed lung is on the injured side and the opposite lung is compressed by the deflected mediastinum. This dangerous condition is called a tension pneumothorax. Air in the pleural cavity associated with serous fluid is known as hydropneumothorax, associated with pus as pyopneumothorax, and associated with blood as hemopneumothorax. A collection of pus (without air) in the pleural cavity is called an empyema. The presence of serous fluid in the pleural cavity is referred to as a pleural effusion (Fig. 3-9). Fluid (serous, blood, or pus) can be drained from the pleural cavity through a wide-bore needle, as described on page 60. In hemopneumothorax, blood enters the pleural cavity. It can be caused by stab or bullet wounds to the chest wall, resulting in bleeding from blood vessels in the chest wall, from vessels in the chest cavity, or from a lacerated lung. P.86

Figure 3-9 Case of right-sided pleural effusion. The mediastinum is displaced to the left, the right lung is compressed, and the bronchi are narrowed. Auscultation would reveal only faint breath sounds over the compressed lung and absent breath sounds over fluid in the pleural cavity.
Figure 3-10 Thoracic part of the trachea. Note that the right principal bronchus is wider and has a more direct continuation of the trachea than the left. Bifurcation of the trachea viewed from above is also shown.

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Trachea The trachea is a mobile cartilaginous and membranous tube (Fig. 3-10). It begins in the neck as a continuation of the larynx at the lower border of the cricoid cartilage at the level of the sixth cervical vertebra. It descends in the midline of the neck. In the thorax the trachea ends below at the carina by dividing into right and left principal (main) bronchi at the level of the sternal angle (opposite the disc between the fourth and fifth thoracic vertebrae). During expiration the bifurcation rises by about one vertebral level, and during deep inspiration may be lowered as far as the sixth thoracic vertebra. In adults the trachea is about 4½ in. (11.25 cm) long and 1 in. (2.5 cm) in diameter (Fig. 3-10). The fibroelastic tube is kept patent by the presence of U-shaped bars (rings) of hyaline cartilage embedded in its wall. The posterior free ends of the cartilage are connected by smooth muscle, the trachealis muscle. The relations of the trachea in the neck are described on page 810.

Figure 3-11 A. How the intercostal muscles raise the ribs during inspiration. Note that the scaleni muscles fix the first rib or, in forced inspiration, raise the first rib. B. How the intercostal muscles can be used in forced expiration, provided that the 12th rib is fixed or is made to descend by the abdominal muscles. C. How the liver provides the platform that enables the diaphragm to raise the lower ribs.

The relations of the trachea in the superior mediastinum of the thorax are as follows:

  • Anteriorly: The sternum, the thymus, the left brachiocephalic vein, the origins of the brachiocephalic and left common carotid arteries, and the arch of the aorta (Figs. 3-6A, 3-10, and 3-31)
  • Posteriorly: The esophagus and the left recurrent laryngeal nerve (Fig. 3-6A)
  • Right side: The azygos vein, the right vagus nerve, and the pleura (Figs. 3-6, 3-16A, and 3-17)
  • Left side: The arch of the aorta, the left common carotid and left subclavian arteries, the left vagus and left phrenic nerves, and the pleura (Figs. 3-6, 3-16B, and 3-18)

Blood Supply of the Trachea The upper two thirds are supplied by the inferior thyroid arteries and the lower third is supplied by the bronchial arteries. P.88
Lymph Drainage of the Trachea The lymph drains into the pretracheal and paratracheal lymph nodes and the deep cervical nodes. Nerve Supply of the Trachea The sensory nerve supply is from the vagi and the recurrent laryngeal nerves. Sympathetic nerves supply the trachealis muscle. The Bronchi The trachea bifurcates behind the arch of the aorta into the right and left principal (primary, or main) bronchi (Figs. 3-10, 3-19, and 3-20). The bronchi divide dichotomously, giving rise to several million terminal bronchioles that terminate in one or more respiratory bronchioles. Each respiratory bronchiole divides into 2 to 11 alveolar ducts that enter the alveolar sacs. The alveoli arise from the walls of the sacs as diverticula (see page 94). Principal Bronchi The right principal (main) bronchus (Fig. 3-12) is wider, shorter, and more vertical than the left (Figs. 3-10, 3-19, and 3-20) and is about 1 in. (2.5 cm) long. Before entering the hilum of the right lung, the principal bronchus gives off the superior lobar bronchus. On entering the hilum, it divides into a middle and an inferior lobar bronchus.

Figure 3-12 Relationship of the pulmonary arteries to the bronchial tree.

The left principal (main) bronchus is narrower, longer, and more horizontal than the right and is about 2 in. (5 cm) long. It passes to the left below the arch of the aorta and in front of the esophagus. On entering the hilum of the left lung, the principal bronchus divides into a superior and an inferior lobar bronchus. Clinical Notes Compression of the Trachea The trachea is a membranous tube kept patent under normal conditions by U-shaped bars of cartilage. In the neck, a unilateral or bilateral enlargement of the thyroid gland can cause gross displacement or compression of the trachea. A dilatation of the aortic arch (aneurysm) can compress the trachea. With each cardiac systole the pulsating aneurysm may tug at the trachea and left bronchus, a clinical sign that can be felt by palpating the trachea in the suprasternal notch. Tracheitis or Bronchitis The mucosa lining the trachea is innervated by the recurrent laryngeal nerve and, in the region of its bifurcation, by the pulmonary plexus. A tracheitis or bronchitis gives rise to a raw, burning sensation felt deep to the sternum instead of actual pain. Many thoracic and abdominal viscera, when diseased, give rise to discomfort that is felt in the midline (see page 280). It seems that organs possessing a sensory innervation that is not under normal conditions directly relayed to consciousness display this phenomenon. The afferent fibers from these organs traveling to the central nervous system accompany autonomic nerves. Inhaled Foreign Bodies Inhalation of foreign bodies into the lower respiratory tract is common, especially in children. Pins, screws, nuts, bolts, peanuts, and parts of chicken bones and toys have all found their way into the bronchi. Parts of teeth may be inhaled while a patient is under anesthesia during a difficult dental extraction. Because the right bronchus is the wider and more direct continuation of the trachea (Figs. 3-19 and 3-20), foreign bodies tend to enter the right instead of the left bronchus. From there, they usually pass into the middle or lower lobe bronchi. Bronchoscopy Bronchoscopy enables a physician to examine the interior of the trachea; its bifurcation, called the carina; and the main bronchi (Figs. 3-13 and 3-14). With experience, it is possible to examine the interior of the lobar bronchi and the beginning of the first segmental bronchi. By means of this procedure, it is also possible to obtain biopsy specimens of mucous membrane and to remove inhaled foreign bodies (even an open safety pin). Lodgment of a foreign body in the larynx or edema of the mucous membrane of the larynx secondary to infection or trauma may require immediate relief to prevent asphyxiation. A method commonly used to relieve complete obstruction is tracheostomy (see page 813). P.89

Figure 3-13 The bifurcation of the trachea as seen through an operating bronchoscope. Note the ridge of the carina in the center and the opening into the right main bronchus on the right, which is a more direct continuation of the trachea. (Courtesy of E.D. Andersen.)
Figure 3-14 The interior of the left main bronchus as seen through an operating bronchoscope. The openings into the left upper lobe bronchus and its division and the left lower lobe bronchus are indicated. (Courtesy of E.D. Andersen.)

Lungs During life, the right and left lungs are soft and spongy and very elastic. If the thoracic cavity were opened, the lungs would immediately shrink to one third or less in volume. In the child, they are pink, but with age, they become dark and mottled because of the inhalation of dust particles that become trapped in the phagocytes of the lung. This is especially well seen in city dwellers and coal miners. The lungs are situated so that one lies on each side of the mediastinum. They are therefore separated from each other by the heart and great vessels and other structures in the mediastinum. Each lung is conical, covered with visceral pleura, and suspended free in its own pleural cavity, being attached to the mediastinum only by its root (Fig. 3-4).

Figure 3-15 Position of the heart valves. P, pulmonary valve; A, aortic valve; M, mitral valve; T, tricuspid valve. Arrows indicate position where valves may be heard with least interference.

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Figure 3-16 A. Right side of the mediastinum. B. Left side of the mediastinum.

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Figure 3-17 Dissection of the right side of the mediastinum; the right lung and the pericardium have been removed. The costal parietal pleura has also been removed.
Figure 3-18 Dissection of the left side of the mediastinum; the left lung and the pericardium have been removed. The costal parietal pleura has also been removed.

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Figure 3-19 Trachea, bronchi, bronchioles, alveolar ducts, alveolar sacs, and alveoli. Note the path taken by inspired air from the trachea to the alveoli.

Each lung has a blunt apex, which projects upward into the neck for about 1 in. (2.5 cm) above the clavicle; a concave base that sits on the diaphragm; a convex costal surface, which corresponds to the concave chest wall; and a concave mediastinal surface, which is molded to the pericardium and other mediastinal structures (Figs. 3-21 and 3-22). At about the middle of this surface is the hilum, a depression in which the bronchi, vessels, and nerves that form the root enter and leave the lung. The anterior border is thin and overlaps the heart; it is here on the left lung that the cardiac notch is found. The posterior border is thick and lies beside the vertebral column. Lobes and Fissures Right Lung The right lung is slightly larger than the left and is divided by the oblique and horizontal fissures into three lobes: the upper, middle, and lower lobes (Fig. 3-21). The oblique fissure runs from the inferior border upward and backward across the medial and costal surfaces until it cuts the posterior border about 2.5 in. (6.25 cm) below the apex. The horizontal fissure runs horizontally across the costal surface at the level of the fourth costal cartilage to meet the oblique fissure in the midaxillary line. The middle lobe is thus a small triangular lobe bounded by the horizontal and oblique fissures. P.93

Figure 3-20 A plastinized specimen of an adult trachea, principal bronchi, and lung; some of the lung tissue has been dissected to reveal the larger bronchi. Note that the right main bronchus is wider and a more direct continuation of the trachea than the left main bronchus.

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Figure 3-21 Lateral and medial surfaces of the right lung.

Left Lung The left lung is divided by a similar oblique fissure into two lobes: the upper and lower lobes (Fig. 3-22). There is no horizontal fissure in the left lung. Bronchopulmonary Segments The bronchopulmonary segments are the anatomic, functional, and surgical units of the lungs. Each lobar (secondary) bronchus, which passes to a lobe of the lung, gives off branches called segmental (tertiary) bronchi (Fig. 3-19). Each segmental bronchus passes to a structurally and functionally independent unit of a lung lobe called a bronchopulmonary segment, which is surrounded by connective tissue (Fig. 3-23). The segmental bronchus is accompanied by a branch of the pulmonary artery, but the tributaries of the pulmonary veins run in the connective tissue between adjacent bronchopulmonary segments. Each segment has its own lymphatic vessels and autonomic nerve supply. On entering a bronchopulmonary segment, each segmental bronchus divides repeatedly (Fig. 3-23). As the bronchi become smaller, the U-shaped bars of cartilage found in the trachea are gradually replaced by irregular plates of cartilage, which become smaller and fewer in number. The smallest bronchi divide and give rise to bronchioles, which are less than 1 mm in diameter (Fig. 3-23). Bronchioles possess no cartilage in their walls and are lined with columnar ciliated epithelium. The submucosa possesses a complete layer of circularly arranged smooth muscle fibers. The bronchioles then divide and give rise to terminal bronchioles (Fig. 3-23), which show delicate outpouchings from their walls. Gaseous exchange between blood and air takes place in the walls of these outpouchings, which explains the name respiratory bronchiole. The diameter of a respiratory bronchiole is about 0.5 mm. The respiratory bronchioles end by branching into alveolar ducts, which lead into tubular passages with numerous thin-walled outpouchings called alveolar sacs. The alveolar sacs consist of several alveoli opening into a single chamber (Figs. 3-23 and 3-24). Each alveolus is surrounded by a rich network of blood capillaries. Gaseous exchange takes place between the air in the alveolar lumen through the alveolar wall into the blood within the surrounding capillaries. P.95

Figure 3-22 Lateral and medial surfaces of the left lung.
Figure 3-23 A bronchopulmonary segment and a lung lobule. Note that the pulmonary veins lie within the connective tissue septa that separate adjacent segments.

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Figure 3-24 Scanning electron micrograph of the lung showing numerous alveolar sacs. The alveoli are the depressions, or alcoves, along the walls of the alveolar sac. (Courtesy of Dr. M. Koering.)

The main characteristics of a bronchopulmonary segment may be summarized as follows:

  • It is a subdivision of a lung lobe.
  • It is pyramid shaped, with its apex toward the lung root.
  • It is surrounded by connective tissue.
  • It has a segmental bronchus, a segmental artery, lymph vessels, and autonomic nerves.
  • The segmental vein lies in the connective tissue between adjacent bronchopulmonary segments.
  • Because it is a structural unit, a diseased segment can be removed surgically.

The main bronchopulmonary segments (Figs. 3-25 and 3-26) are as follows:

  • Right lung Superior lobe: Apical, posterior, anterior Middle lobe: Lateral, medial Inferior lobe: Superior (apical), medial basal, anterior basal, lateral basal, posterior basal
  • Left lung Superior lobe: Apical, posterior, anterior, superior lingular, inferior lingular Inferior lobe: Superior (apical), medial basal, anterior basal, lateral basal, posterior basal

Although the general arrangement of the bronchopulmonary segments is of clinical importance, it is unnecessary to memorize the details unless one intends to specialize in pulmonary medicine or surgery. The root of the lung is formed of structures that are entering or leaving the lung. It is made up of the bronchi, pulmonary artery and veins, lymph vessels, bronchial vessels, and nerves. The root is surrounded by a tubular sheath of pleura, which joins the mediastinal parietal pleura to the visceral pleura covering the lungs (Figs. 3-5, 3-16, 3-17, and 3-18). Blood Supply of the Lungs The bronchi, the connective tissue of the lung, and the visceral pleura receive their blood supply from the bronchial arteries, which are branches of the descending aorta. The bronchial veins (which communicate with the pulmonary veins) drain into the azygos and hemiazygos veins. P.97

Figure 3-25 Lungs viewed from the right. A. Lobes. B. Bronchopulmonary segments.
Figure 3-26 Lungs viewed from the left. A. Lobes. B. Bronchopulmonary segments.

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The alveoli receive deoxygenated blood from the terminal branches of the pulmonary arteries. The oxygenated blood leaving the alveolar capillaries drains into the tributaries of the pulmonary veins, which follow the intersegmental connective tissue septa to the lung root. Two pulmonary veins leave each lung root (Fig. 3-16) to empty into the left atrium of the heart. Lymph Drainage of the Lungs The lymph vessels originate in superficial and deep plexuses (Fig. 3-27); they are not present in the alveolar walls. The superficial (subpleural) plexus lies beneath the visceral pleura and drains over the surface of the lung toward the hilum, where the lymph vessels enter the bronchopulmonary nodes. The deep plexus travels along the bronchi and pulmonary vessels toward the hilum of the lung, passing through pulmonary nodes located within the lung substance; the lymph then enters the bronchopulmonary nodes in the hilum of the lung. All the lymph from the lung leaves the hilum and drains into the tracheobronchial nodes and then into the bronchomediastinal lymph trunks.

Figure 3-27 Lymph drainage of the lung and lower end of the esophagus.

Nerve Supply of the Lungs At the root of each lung is a pulmonary plexus composed of efferent and afferent autonomic nerve fibers. The plexus is formed from branches of the sympathetic trunk and receives parasympathetic fibers from the vagus nerve. The sympathetic efferent fibers produce bronchodilatation and vasoconstriction. The parasympathetic efferent fibers produce bronchoconstriction, vasodilatation, and increased glandular secretion. Afferent impulses derived from the bronchial mucous membrane and from stretch receptors in the alveolar walls pass to the central nervous system in both sympathetic and parasympathetic nerves. Embryologic Notes Development of the Lungs and Pleura A longitudinal groove develops in the entodermal lining of the floor of the pharynx. This groove is known as the laryngotracheal groove. The lining of the larynx, trachea, and bronchi and the epithelium of the alveoli develop from this groove. The margins of the groove fuse and form the laryngotracheal tube (Fig. 3-28). The fusion process starts distally so that the lumen becomes separated from the developing esophagus. Just behind the developing tongue, a small opening persists that will become the permanent opening into the larynx. The laryngotracheal tube grows caudally into the splanchnic mesoderm and will eventually lie anterior to the esophagus. The tube divides distally into the right and left lung buds. Cartilage develops in the mesenchyme surrounding the tube, and the upper part of the tube becomes the larynx, whereas the lower part becomes the trachea. Each lung bud consists of an entodermal tube surrounded by splanchnic mesoderm; from this, all the tissues of the corresponding lung are derived. Each bud grows laterally and projects into the pleural part of the embryonic coelom (Fig. 3-28). The lung bud divides into three lobes and then into two, corresponding to the number of main bronchi and lobes found in the fully developed lung. Each main bronchus then divides repeatedly in a dichotomous manner, until eventually the terminal bronchioles and alveoli are formed. The division of the terminal bronchioles, with the formation of additional bronchioles and alveoli, continues for some time after birth. Each lung will receive a covering of visceral pleura derived from the splanchnic mesoderm. The parietal pleura will be formed from somatic mesoderm. By the seventh month, the capillary loops connected with the pulmonary circulation have become sufficiently well developed to support life, should premature birth take place. With the onset of respiration at birth, the lungs expand and the alveoli become dilated. However, it is only after 3 or 4 days of postnatal life that the alveoli in the periphery of each lung become fully expanded. Congenital Anomalies Esophageal Atresia and Tracheoesophageal Fistula If the margins of the laryngotracheal groove fail to fuse adequately, an abnormal opening may be left between the laryngotracheal tube and the esophagus. If the tracheoesophageal septum formed by the fusion of the margins of the laryngotracheal groove should be deviated posteriorly, the lumen of the esophagus would be much reduced in diameter. The different types of atresia, with and without fistula, are shown in Figure 3-29. Obstruction of the esophagus prevents the child from swallowing saliva and milk, and this leads to aspiration into the larynx and trachea, which usually results in pneumonia. With early diagnosis, it is often possible to correct this serious anomaly surgically. P.99

Figure 3-28 The development of the lungs. A. The laryngotracheal groove and tube have been formed. B. The margins of the laryngotracheal groove fuse to form the laryngotracheal tube. C. The lung buds invaginate the wall of the intraembryonic coelom. D. The lung buds divide to form the main bronchi.

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Figure 3-29 Different types of esophageal atresia and tracheoesophageal fistula. A. Complete blockage of the esophagus with a tracheoesophageal fistula. B. Similar to type A, but the two parts of the esophagus are joined together by fibrous tissue. C. Complete blockage of the esophagus; the distal end is rudimentary. D. A tracheoesophageal fistula with narrowing of the esophagus. E. An esophagotracheal fistula; the esophagus is not connected with the distal end, which is rudimentary. F. Separate esophagotracheal and tracheoesophageal fistulas. G. Narrowing of the esophagus without a fistula. In most cases, the lower esophageal segment communicates with the trachea, and types A and B occur more commonly.

The Mechanics of Respiration Respiration consists of two phases—inspiration and expiration—which are accomplished by the alternate increase and decrease of the capacity of the thoracic cavity. The rate varies between 16 and 20 per minute in normal resting patients and is faster in children and slower in the elderly. Inspiration Quiet Inspiration Compare the thoracic cavity to a box with a single entrance at the top, which is a tube called the trachea (Fig. 3-30). The capacity of the box can be increased by elongating all its diameters, and this results in air under atmospheric pressure entering the box through the tube. Consider now the three diameters of the thoracic cavity and how they may be increased (Fig. 3-30). Vertical Diameter Theoretically, the roof could be raised and the floor lowered. The roof is formed by the suprapleural membrane and is fixed. Conversely, the floor is formed by the mobile diaphragm. When the diaphragm contracts, the domes become flattened and the level of the diaphragm is lowered (Fig. 3-30). Anteroposterior Diameter If the downward-sloping ribs were raised at their sternal ends, the anteroposterior diameter of the thoracic cavity would be increased and the lower end of the sternum would be thrust forward (Fig. 3-30). This can be brought about by fixing the first rib by the contraction of the scaleni muscles of the neck and contracting the intercostal muscles (Fig. 3-11). By this means, all the ribs are drawn together and raised toward the first rib. Transverse Diameter The ribs articulate in front with the sternum via their costal cartilages and behind with the vertebral column. Because the ribs curve downward as well as forward around the chest wall, they resemble bucket handles (Fig. 3-30). It therefore follows that if the ribs are raised (like bucket handles), the transverse diameter of the thoracic cavity will be increased. As described previously, this can be accomplished by fixing the first rib and raising the other ribs to it by contracting the intercostal muscles (Fig. 3-11). An additional factor that must not be overlooked is the effect of the descent of the diaphragm on the abdominal viscera and the tone of the muscles of the anterior abdominal wall. As the diaphragm descends on inspiration, intraabdominal pressure rises. This rise in pressure is accommodated by the reciprocal relaxation of the abdominal wall musculature. However, a point is reached when no further abdominal relaxation is possible, and the liver and other upper abdominal viscera act as a platform that resists further diaphragmatic descent. On further contraction, the diaphragm will now have its central tendon supported from below, and its shortening muscle fibers will assist the intercostal muscles in raising the lower ribs (Fig. 3-11). P.101

Figure 3-30 The different ways in which the capacity of the thoracic cavity is increased during inspiration.

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Apart from the diaphragm and the intercostals, other less important muscles also contract on inspiration and assist in elevating the ribs, namely, the levatores costarum muscles and the serratus posterior superior muscles. Forced Inspiration In deep forced inspiration, a maximum increase in the capacity of the thoracic cavity occurs. Every muscle that can raise the ribs is brought into action, including the scalenus anterior and medius and the sternocleidomastoid. In respiratory distress the action of all the muscles already engaged becomes more violent, and the scapulae are fixed by the trapezius, levator scapulae, and rhomboid muscles, enabling the serratus anterior and pectoralis minor to pull up the ribs. If the upper limbs can be supported by grasping a chair back or table, the sternal origin of the pectoralis major muscles can also assist the process. Lung Changes on Inspiration In inspiration, the root of the lung descends and the level of the bifurcation of the trachea may be lowered by as much as two vertebrae. The bronchi elongate and dilate and the alveolar capillaries dilate, thus assisting the pulmonary circulation. Air is drawn into the bronchial tree as the result of the positive atmospheric pressure exerted through the upper part of the respiratory tract and the negative pressure on the outer surface of the lungs brought about by the increased capacity of the thoracic cavity. With expansion of the lungs, the elastic tissue in the bronchial walls and connective tissue are stretched. As the diaphragm descends, the costodiaphragmatic recess of the pleural cavity opens, and the expanding sharp lower edges of the lungs descend to a lower level. Expiration Quiet Expiration Quiet expiration is largely a passive phenomenon and is brought about by the elastic recoil of the lungs, the relaxation of the intercostal muscles and diaphragm, and an increase in tone of the muscles of the anterior abdominal wall, which forces the relaxing diaphragm upward. The serratus posterior inferior muscles play a minor role in pulling down the lower ribs. Forced Expiration Forced expiration is an active process brought about by the forcible contraction of the musculature of the anterior abdominal wall. The quadratus lumborum also contracts and pulls down the 12th ribs. It is conceivable that under these circumstances some of the intercostal muscles may contract, pull the ribs together, and depress them to the lowered 12th rib (Fig. 3-11). The serratus posterior inferior and the latissimus dorsi muscles may also play a minor role. Lung Changes on Expiration In expiration, the roots of the lungs ascend along with the bifurcation of the trachea. The bronchi shorten and contract. The elastic tissue of the lungs recoils, and the lungs become reduced in size. With the upward movement of the diaphragm, increasing areas of the diaphragmatic and costal parietal pleura come into apposition, and the costodiaphragmatic recess becomes reduced in size. The lower margins of the lungs shrink and rise to a higher level. Types of Respiration In babies and young children, the ribs are nearly horizontal. Thus, babies have to rely mainly on the descent of the diaphragm to increase their thoracic capacity on inspiration. Because this is accompanied by a marked inward and outward excursion of the anterior abdominal wall, which is easily seen, respiration at this age is referred to as the abdominal type of respiration. After the second year of life, the ribs become more oblique, and the adult form of respiration is established. In the adult a sexual difference exists in the type of respiratory movements. The female tends to rely mainly on the movements of the ribs rather than on the descent of the diaphragm on inspiration. This is referred to as the thoracic type of respiration. The male uses both the thoracic and abdominal forms of respiration, but mainly the abdominal form. Clinical Notes Physical Examination of the Lungs For physical examination of the patient, it is helpful to remember that the upper lobes of the lungs are most easily examined from the front of the chest and the lower lobes from the back. In the axillae, areas of all lobes can be examined. Trauma to the Lungs A physician must always remember that the apex of the lung projects up into the neck (1 in. [2.5 cm] above the clavicle) and can be damaged by stab or bullet wounds in this area. Although the lungs are well protected by the bony thoracic cage, a splinter from a fractured rib can nevertheless penetrate the lung, and air can escape into the pleural cavity, causing a pneumothorax and collapse of the lung. It can also find its way into the lung connective tissue. From there, the air moves under the visceral pleura until it reaches the lung root. It then passes into the mediastinum and up to the neck. Here, it may distend the subcutaneous tissue, a condition known as subcutaneous emphysema. The changes in the position of the thoracic and upper abdominal viscera and the level of the diaphragm during different phases of respiration relative to the chest wall are of considerable clinical importance. A penetrating wound in the lower part of the chest may or may not damage abdominal viscera, depending on the phase of respiration at the time of injury. Pain and Lung Disease Lung tissue and the visceral pleura are devoid of pain-sensitive nerve endings, so that pain in the chest is always the result of conditions affecting the surrounding structures. In tuberculosis or pneumonia, for example, pain may never be experienced. Once lung disease crosses the visceral pleura and the pleural cavity to involve the parietal pleura, pain becomes a prominent feature. Lobar pneumonia with pleurisy, for example, produces a severe tearing pain, accentuated by inspiring deeply or coughing. Because the lower part of the costal parietal pleura receives its sensory innervation from the lower five intercostal nerves, which also innervate the skin of the anterior abdominal wall, pleurisy in this area commonly produces pain that is referred to the abdomen. This has sometimes resulted in a mistaken diagnosis of an acute abdominal lesion. In a similar manner, pleurisy of the central part of the diaphragmatic pleura, which receives sensory innervation from the phrenic nerve (C3, 4, and 5), can lead to referred pain over the shoulder because the skin of this region is supplied by the supraclavicular nerves (C3 and 4). Surgical Access to the Lungs Surgical access to the lung or mediastinum is commonly undertaken through an intercostal space (see page 60). Special rib retractors that allow the ribs to be widely separated are used. The costal cartilages are sufficiently elastic to permit considerable bending. Good exposure of the lungs is obtained by this method. Segmental Resection of the Lung A localized chronic lesion such as that of tuberculosis or a benign neoplasm may require surgical removal. If it is restricted to a bronchopulmonary segment, it is possible carefully to dissect out a particular segment and remove it, leaving the surrounding lung intact. Segmental resection requires that the radiologist and thoracic surgeon have a sound knowledge of the bronchopulmonary segments and that they cooperate fully to localize the lesion accurately before operation. Bronchogenic Carcinoma Bronchogenic carcinoma accounts for about one third of all cancer deaths in men and is becoming increasingly common in women. It commences in most patients in the mucous membrane lining the larger bronchi and is therefore situated close to the hilum of the lung. The neoplasm rapidly spreads to the tracheobronchial and bronchomediastinal nodes and may involve the recurrent laryngeal nerves, leading to hoarseness of the voice. Lymphatic spread via the bronchomediastinal trunks may result in early involvement in the lower deep cervical nodes just above the level of the clavicle. Hematogenous spread to bones and the brain commonly occurs. Conditions That Decrease Respiratory Efficiency Constriction of the Bronchi (Bronchial Asthma) One of the problems associated with bronchial asthma is the spasm of the smooth muscle in the wall of the bronchioles. This particularly reduces the diameter of the bronchioles during expiration, usually causing the asthmatic patient to experience great difficulty in expiring, although inspiration is accomplished normally. The lungs consequently become greatly distended and the thoracic cage becomes permanently enlarged, forming the so-called barrel chest. In addition, the air flow through the bronchioles is further impeded by the presence of excess mucus, which the patient is unable to clear because an effective cough cannot be produced. Loss of Lung Elasticity Many diseases of the lungs, such as emphysema and pulmonary fibrosis, destroy the elasticity of the lungs, and thus the lungs are unable to recoil adequately, causing incomplete expiration. The respiratory muscles in these patients have to assist in expiration, which no longer is a passive phenomenon. Loss of Lung Distensibility Diseases such as silicosis, asbestosis, cancer, and pneumonia interfere with the process of expanding the lung in inspiration. A decrease in the compliance of the lungs and the chest wall then occurs, and a greater effort has to be undertaken by the inspiratory muscles to inflate the lungs. Postural Drainage Excessive accumulation of bronchial secretions in a lobe or segment of a lung can seriously interfere with the normal flow of air into the alveoli. Furthermore, the stagnation of such secretions is often quickly followed by infection. To aid in the normal drainage of a bronchial segment, a physiotherapist often alters the position of the patient so that gravity assists in the process of drainage. Sound knowledge of the bronchial tree is necessary to determine the optimum position of the patient for good postural drainage. P.103
Pericardium The pericardium is a fibroserous sac that encloses the heart and the roots of the great vessels. Its function is to restrict excessive movements of the heart as a whole and to serve as a lubricated container in which the different parts of the heart can contract. The pericardium lies within the middle mediastinum (Figs. 3-2, 3-31, 3-32, and 3-33), posterior to the body of the sternum and the second to the sixth costal cartilages and anterior to the fifth to the eighth thoracic vertebrae. Fibrous Pericardium The fibrous pericardium is the strong fibrous part of the sac. It is firmly attached below to the central tendon of the diaphragm. It fuses with the outer coats of the great blood vessels passing through it (Fig. 3-32)—namely, the aorta, the pulmonary trunk, the superior and inferior venae cavae, and the pulmonary veins (Fig. 3-33). The fibrous pericardium is attached in front to the sternum by the sternopericardial ligaments. Serous Pericardium The serous pericardium lines the fibrous pericardium and coats the heart. It is divided into parietal and visceral layers (Fig. 3-32). The parietal layer lines the fibrous pericardium and is reflected around the roots of the great vessels to become P.104
continuous with the visceral layer of serous pericardium that closely covers the heart (Fig. 3-33).

Figure 3-31 The pericardium and the lungs exposed from in front.
Figure 3-32 Different layers of the pericardium.

The visceral layer is closely applied to the heart and is often called the epicardium. The slitlike space between the parietal and visceral layers is referred to as the pericardial cavity (Fig. 3-32). Normally, the cavity contains a small amount of tissue fluid (about 50 mL), the pericardial fluid, which acts as a lubricant to facilitate movements of the heart. Pericardial Sinuses On the posterior surface of the heart, the reflection of the serous pericardium around the large veins forms a recess called the oblique sinus (Fig. 3-33). Also on the posterior surface of the heart is the transverse sinus, which is a short passage that lies between the reflection of serous pericardium around the aorta and pulmonary trunk and the reflection around the large veins (Fig. 3-33). The pericardial sinuses form as a consequence of the way the heart bends during development (see page 118). They have no clinical significance. Nerve Supply of the Pericardium The fibrous pericardium and the parietal layer of the serous pericardium are supplied by the phrenic nerves. The visceral layer of the serous pericardium is innervated by branches of the sympathetic trunks and the vagus nerves. P.105

Figure 3-33 The great blood vessels and the interior of the pericardium.

Clinical Notes Pericarditis In inflammation of the serous pericardium, called pericarditis, pericardial fluid may accumulate excessively, which can compress the thin-walled atria and interfere with the filling of the heart during diastole. This compression of the heart is called cardiac tamponade. Cardiac tamponade can also occur secondary to stab or gunshot wounds when the chambers of the heart have been penetrated. The blood escapes into the pericardial cavity and can restrict the filling of the heart. Roughening of the visceral and parietal layers of serous pericardium by inflammatory exudate in acute pericarditis produces pericardial friction rub, which can be felt on palpation and heard through a stethoscope. Pericardial fluid can be aspirated from the pericardial cavity should excessive amounts accumulate in pericarditis. This process is called paracentesis. The needle can be introduced to the left of the xiphoid process in an upward and backward direction at an angle of 45° to the skin. When paracentesis is performed at this site, the pleura and lung are not damaged because of the presence of the cardiac notch in this area. Heart The heart is a hollow muscular organ that is somewhat pyramid shaped and lies within the pericardium in the mediastinum (Figs. 3-34 and 3-35). It is connected at its base to the great blood vessels but otherwise lies free within the pericardium. Surfaces of the Heart The heart has three surfaces: sternocostal (anterior), diaphragmatic (inferior), and a base (posterior). It also has an apex, which is directed downward, forward, and to the left. The sternocostal surface is formed mainly by the right atrium and the right ventricle, which are separated from each other by the vertical atrioventricular groove (Fig. 3-35). The right border is formed by the right atrium; the left border, by the left ventricle and part of the left auricle. The right ventricle is separated from the left ventricle by the anterior interventricular groove. The diaphragmatic surface of the heart is formed mainly by the right and left ventricles separated by the posterior interventricular groove. The inferior surface of the right atrium, into which the inferior vena cava opens, also forms part of this surface. The base of the heart, or the posterior surface, is formed mainly by the left atrium, into which open the four pulmonary veins (Fig. 3-36). The base of the heart lies opposite the apex. P.106

Figure 3-34 The anterior surface of the heart; the fibrous pericardium and the parietal serous pericardium have been removed. Note the presence of fat beneath the visceral serous pericardium in the atrioventricular and interventricular grooves. The coronary arteries are embedded in this fat.
Figure 3-35 The anterior surface of the heart and the great blood vessels. Note the course of the coronary arteries and the cardiac veins.

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Figure 3-36 The posterior surface, or the base, of the heart.

The apex of the heart, formed by the left ventricle, is directed downward, forward, and to the left (Fig. 3-35). It lies at the level of the fifth left intercostal space, 3.5 in. (9 cm) from the midline. In the region of the apex, the apex beat can usually be seen and palpated in the living patient. Note that the base of the heart is called the base because the heart is pyramid shaped; the base lies opposite the apex. The heart does not rest on its base; it rests on its diaphragmatic (inferior) surface. Borders of the Heart The right border is formed by the right atrium; the left border, by the left auricle; and below, by the left ventricle (Fig. 3-35). The lower border is formed mainly by the right ventricle but also by the right atrium; the apex is formed by the left ventricle. These borders are important to recognize when examining a radiograph of the heart. Chambers of the Heart The heart is divided by vertical septa into four chambers: the right and left atria and the right and left ventricles. The right atrium lies anterior to the left atrium, and the right ventricle lies anterior to the left ventricle. The walls of the heart are composed of cardiac muscle, the myocardium; covered externally with serous pericardium, the epicardium; and lined internally with a layer of endothelium, the endocardium. Right Atrium The right atrium consists of a main cavity and a small outpouching, the auricle (Figs. 3-35 and 3-37). On the outside of the heart at the junction between the right atrium and the right auricle is a vertical groove, the sulcus terminalis, which on the inside forms a ridge, the crista terminalis. The main part of the atrium that lies posterior to the ridge is smooth walled and is derived embryologically from the sinus venosus. The part of the atrium in front of the ridge is roughened or trabeculated by bundles of muscle fibers, the musculi pectinati, which run from the crista terminalis to the auricle. This anterior part is derived embryologically from the primitive atrium. Openings into the Right Atrium The superior vena cava (Fig. 3-37) opens into the upper part of the right atrium; it has no valve. It returns the blood to the heart from the upper half of the body. The inferior vena cava (larger than the superior vena cava) opens into the lower part of the right atrium; it is guarded by a rudimentary, nonfunctioning valve. It returns the blood to the heart from the lower half of the body. The coronary sinus, which drains most of the blood from the heart wall (Fig. 3-37), opens into the right atrium between the inferior vena cava and the atrioventricular orifice. It is guarded by a rudimentary, nonfunctioning valve. The right atrioventricular orifice lies anterior to the inferior vena caval opening and is guarded by the tricuspid valve (Fig. 3-37). Many small orifices of small veins also drain the wall of the heart and open directly into the right atrium. Fetal Remnants In addition to the rudimentary valve of the inferior vena cava are the fossa ovalis and anulus ovalis. These latter structures lie on the atrial septum, which separates the right atrium from the left atrium (Fig. 3-37). The fossa ovalis is a shallow depression, which is the site of the foramen P.108
ovale in the fetus (Fig. 3-38). The anulus ovalis forms the upper margin of the fossa. The floor of the fossa represents the persistent septum primum of the heart of the embryo, and the anulus is formed from the lower edge of the septum secundum (Fig. 3-38).

Figure 3-37 Interior of the right atrium and the right ventricle. Note the positions of the sinuatrial node and the atrioventricular node and bundle.

Right Ventricle The right ventricle communicates with the right atrium through the atrioventricular orifice and with the pulmonary trunk through the pulmonary orifice (Fig. 3-37). As the cavity approaches the pulmonary orifice it becomes funnel shaped, at which point it is referred to as the infundibulum. The walls of the right ventricle are much thicker than those of the right atrium and show several internal projecting ridges formed of muscle bundles. The projecting ridges give the ventricular wall a spongelike appearance and are known as trabeculae carneae. The trabeculae carneae are composed of three types. The first type comprises the papillary muscles, which project inward, being attached by their bases to the ventricular wall; their apices are connected by fibrous chords (the chordae tendineae) to the cusps of the tricuspid valve (Fig. 3-37). The second type is attached at the ends to the ventricular wall, being free in the middle. One of these, the moderator band, crosses the ventricular cavity from the septal to the anterior wall. It conveys the right branch of the atrioventricular bundle, which is part of the conducting system of the heart. The third type is simply composed of prominent ridges. The tricuspid valve guards the atrioventricular orifice (Figs. 3-37 and 3-39) and consists of three cusps formed by a fold of endocardium with some connective tissue enclosed: anterior, septal, and inferior (posterior) cusps. The anterior cusp lies anteriorly, the septal cusp lies against the ventricular septum, and the inferior or posterior cusp lies inferiorly. The bases of the cusps are attached to the fibrous ring of the skeleton of the heart (see below), whereas their free edges and ventricular surfaces are attached to the chordae tendineae. The chordae tendineae connect the cusps to the papillary muscles. When the ventricle contracts, the papillary muscles contract and prevent the cusps from being forced into the atrium and turning inside out as the intraventricular pressure rises. To assist in this process, the chordae tendineae of one papillary muscle are connected to the adjacent parts of two cusps. The pulmonary valve guards the pulmonary orifice (Fig. 3-39A) and consists of three semilunar cusps formed by folds of endocardium with some connective tissue enclosed. The curved lower margins and sides of each cusp are attached to the arterial wall. The open mouths of the cusps are directed upward into the pulmonary trunk. No chordae or papillary muscles are associated with these valve cusps; the attachments of the sides of the cusps to the arterial wall prevent the cusps from prolapsing into the ventricle. At the root of the pulmonary trunk are three dilatations called the sinuses, and one is situated external to each cusp (see aortic valve). The three semilunar cusps are arranged with one posterior (left cusp) and two anterior (anterior and right cusps). P.109
(The cusps of the pulmonary and aortic valves are named according to their position in the fetus before the heart has rotated to the left. This, unfortunately, causes a great deal of unnecessary confusion.) During ventricular systole, the cusps of the valve are pressed against the wall of the pulmonary trunk by the out-rushing blood. During diastole, blood flows back toward the heart and enters the sinuses; the valve cusps fill, come into apposition in the center of the lumen, and close the pulmonary orifice.

Figure 3-38 A. Normal fetal heart. B. Atrial septal defect. C. Tetralogy of Fallot. D. Patent ductus arteriosus (note the close relationship to the left recurrent laryngeal nerve). E. Coarctation of the aorta.

Left Atrium Similar to the right atrium, the left atrium consists of a main cavity and a left auricle. The left atrium is situated behind the right atrium and forms the greater part of the base or the posterior surface of the heart (Fig. 3-36). Behind it lies the oblique sinus of the serous pericardium, and the fibrous pericardium separates it from the esophagus (Figs. 3-33 and 3-40). The interior of the left atrium is smooth, but the left auricle possesses muscular ridges as in the right auricle. P.110

Figure 3-39 A. Position of the tricuspid and pulmonary valves. B. Mitral cusps with valve open. C. Mitral cusps with valve closed. D. Semilunar cusps of the aortic valve. E. Cross section of the ventricles of the heart. F. Path taken by the blood through the heart. G. Path taken by the cardiac impulse from the sinuatrial node to the Purkinje network. H. Fibrous skeleton of the heart.

Openings into the Left Atrium The four pulmonary veins, two from each lung, open through the posterior wall (Fig. 3-36) and have no valves. The left atrioventricular orifice is guarded by the mitral valve. Left Ventricle The left ventricle communicates with the left atrium through the atrioventricular orifice and with the aorta through the aortic orifice. The walls of the left ventricle (Fig. 3-39) are three times thicker than those of the right ventricle. (The left intraventricular blood pressure is six times higher than that inside the right ventricle.) In cross section, the left ventricle is circular; the right is crescentic because of the bulging of the ventricular septum into the cavity of the right ventricle (Fig. 3-39). There are well-developed trabeculae carneae, two large papillary muscles, but no moderator band. The part of the ventricle below the aortic orifice is called the aortic vestibule. P.111

Figure 3-40 Cross section of the thorax at the eighth thoracic vertebra, as seen from below. (Note that all computed tomography scans and magnetic resonance imaging studies are viewed from below.)

The mitral valve guards the atrioventricular orifice (Fig. 3-39). It consists of two cusps, one anterior and one posterior, which have a structure similar to that of the cusps of the tricuspid valve. The anterior cusp is the larger and intervenes between the atrioventricular and the aortic orifices. The attachment of the chordae tendineae to the cusps and the papillary muscles is similar to that of the tricuspid valve. The aortic valve guards the aortic orifice and is precisely similar in structure to the pulmonary valve (Fig. 3-39). One cusp is situated on the anterior wall (right cusp) and two are located on the posterior wall (left and posterior cusps). Behind each cusp the aortic wall bulges to form an aortic sinus. The anterior aortic sinus gives origin to the right coronary artery, and the left posterior sinus gives origin to the left coronary artery. Structure of the Heart The walls of the heart are composed of a thick layer of cardiac muscle, the myocardium, covered externally by the epicardium and lined internally by the endocardium. The atrial portion of the heart has relatively thin walls and is divided by the atrial (interatrial) septum into the right and left atria. The septum runs from the anterior wall of the heart backward and to the right. The ventricular portion of the heart has thick walls and is divided by the ventricular (interventricular) septum into the right and left ventricles. The septum is placed obliquely, with one surface facing forward and to the right and the other facing backward and to the left. Its position is indicated on the surface of the heart by the anterior and posterior interventricular grooves. The lower part of the septum is thick and formed of muscle. The smaller upper part of the septum is thin and membranous and attached to the fibrous skeleton. The so-called skeleton of the heart (Fig. 3-39) consists of fibrous rings that surround the atrioventricular, pulmonary, and aortic orifices and are continuous with the membranous upper part of the ventricular septum. The fibrous rings around the atrioventricular orifices separate the muscular walls of the atria from those of the ventricles but provide attachment for the muscle fibers. The fibrous rings support the bases of the valve cusps and prevent the valves from stretching and becoming incompetent. The skeleton of the heart forms the basis of electrical discontinuity between the atria and the ventricles. Conducting System of the Heart The normal heart contracts rhythmically at about 70 to 90 beats per minute in the resting adult. The rhythmic contractile process originates spontaneously in the conducting system and the impulse travels to different regions of the heart, so the atria contract first and together, to be followed later by the contractions of both ventricles together. The slight delay in the passage of the impulse from the atria to the ventricles allows time for the atria to empty their blood into the ventricles before the ventricles contract. The conducting system of the heart consists of specialized cardiac muscle present in the sinuatrial node, the atrioventricular node, the atrioventricular bundle and its right and left terminal branches, and the subendocardial plexus of Purkinje fibers (specialized cardiac muscle fibers that form the conducting system of the heart). P.112

Figure 3-41 The conducting system of the heart. Note the internodal pathways.

Sinuatrial Node The sinuatrial node is located in the wall of the right atrium in the upper part of the sulcus terminalis just to the right of the opening of the superior vena cava (Figs. 3-37 and 3-39). The node spontaneously gives origin to rhythmic electrical impulses that spread in all directions through the cardiac muscle of the atria and cause the muscle to contract. Atrioventricular Node The atrioventricular node is strategically placed on the lower part of the atrial septum just above the attachment of the septal cusp of the tricuspid valve (Figs. 3-37 and 3-39). From it, the cardiac impulse is conducted to the ventricles by the atrioventricular bundle. The atrioventricular node is stimulated by the excitation wave as it passes through the atrial myocardium. The speed of conduction of the cardiac impulse through the atrioventricular node (about 0.11 seconds) allows sufficient time for the atria to empty their blood into the ventricles before the ventricles start to contract. Atrioventricular Bundle The atrioventricular bundle (bundle of His) is the only pathway of cardiac muscle that connects the myocardium of the atria and the myocardium of the ventricles and is thus the only route along which the cardiac impulse can travel from the atria to the ventricles (Fig. 3-41). The bundle descends through the fibrous skeleton of the heart. The atrioventricular bundle then descends behind the septal cusp of the tricuspid valve to reach the inferior border of the membranous part of the ventricular septum. At the upper border of the muscular part of the septum it divides into two branches, one for each ventricle. The right bundle branch (RBB) passes down on the right side of the ventricular septum to reach the moderator band, where it crosses to the anterior wall of the right ventricle. Here it becomes continuous with the fibers of the Purkinje plexus (Fig. 3-41). The left bundle branch (LBB) pierces the septum and passes down on its left side beneath the endocardium. It usually divides into two branches (anterior and posterior), which eventually become continuous with the fibers of the Purkinje plexus of the left ventricle. It is thus seen that the conducting system of the heart is responsible not only for generating rhythmic cardiac impulses, but also for conducting these impulses rapidly throughout the myocardium of the heart so that the different chambers contract in a coordinated and efficient manner. The activities of the conducting system can be influenced by the autonomic nerve supply to the heart. The parasympathetic nerves slow the rhythm and diminish the rate of conduction of the impulse; the sympathetic nerves have the opposite effect. Internodal Conduction Paths* Impulses from the sinuatrial node have been shown to travel to the atrioventricular node more rapidly than they can travel by passing along the ordinary myocardium. This phenomenon has been explained by the description of special pathways in the atrial wall (Fig. 3-41), which have a structure consisting of a mixture of Purkinje fibers and ordinary cardiac P.113
muscle cells. The anterior internodal pathway leaves the anterior end of the sinuatrial node and passes anterior to the superior vena caval opening. It descends on the atrial septum and ends in the atrioventricular node. The middle internodal pathway leaves the posterior end of the sinuatrial node and passes posterior to the superior vena caval opening. It descends on the atrial septum to the atrioventricular node. The posterior internodal pathway leaves the posterior part of the sinuatrial node and descends through the crista terminalis and the valve of the inferior vena cava to the atrioventricular node. Clinical Notes Failure of the Conduction System of the Heart The sinuatrial node is the spontaneous source of the cardiac impulse. The atrioventricular node is responsible for picking up the cardiac impulse from the atria. The atrioventricular bundle is the only route by which the cardiac impulse can spread from the atria to the ventricles. Failure of the bundle to conduct the normal impulses results in alteration in the rhythmic contraction of the ventricles (arrhythmias) or, if complete bundle block occurs, complete dissociation between the atria and ventricular rates of contraction. The common cause of defective conduction through the bundle or its branches is atherosclerosis of the coronary arteries, which results in a diminished blood supply to the conducting system. Arterial Supply of the Heart The arterial supply of the heart is provided by the right and left coronary arteries, which arise from the ascending aorta immediately above the aortic valve (Fig. 3-42). The coronary arteries and their major branches are distributed over the surface of the heart, lying within subepicardial connective tissue. The right coronary artery arises from the anterior aortic sinus of the ascending aorta and runs forward between the pulmonary trunk and the right auricle (Fig. 3-35). It descends almost vertically in the right atrioventricular groove, and at the inferior border of the heart it continues posteriorly along the atrioventricular groove to anastomose with the left coronary artery in the posterior interventricular groove. The following branches from the right coronary artery supply the right atrium and right ventricle and parts of the left atrium and left ventricle and the atrioventricular septum. Branches

  • The right conus artery supplies the anterior surface of the pulmonary conus (infundibulum of the right ventricle) and the upper part of the anterior wall of the right ventricle.
  • The anterior ventricular branches are two or three in number and supply the anterior surface of the right ventricle. The marginal branch is the largest and runs along the lower margin of the costal surface to reach the apex.
  • The posterior ventricular branches are usually two in number and supply the diaphragmatic surface of the right ventricle.
  • The posterior interventricular (descending) artery runs toward the apex in the posterior interventricular groove. It gives off branches to the right and left ventricles, including its inferior wall. It supplies branches to the posterior part of the ventricular septum but not to the apical part, which receives its supply from the anterior interventricular branch of the left coronary artery. A large septal branch supplies the atrioventricular node. In 10% of individuals the posterior interventricular artery is replaced by a branch from the left coronary artery.
  • The atrial branches supply the anterior and lateral surfaces of the right atrium. One branch supplies the posterior surface of both the right and left atria. The artery of the sinuatrial node supplies the node and the right and left atria; in 35% of individuals it arises from the left coronary artery.

The left coronary artery, which is usually larger than the right coronary artery, supplies the major part of the heart, including the greater part of the left atrium, left ventricle, and ventricular septum. It arises from the left posterior aortic sinus of the ascending aorta and passes forward between the pulmonary trunk and the left auricle (Fig. 3-35). It then enters the atrioventricular groove and divides into an anterior interventricular branch and a circumflex branch. Branches

  • The anterior interventricular (descending) branch runs downward in the anterior interventricular groove to the apex of the heart (Fig. 3-42). In most individuals it then passes around the apex of the heart to enter the posterior interventricular groove and anastomoses with the terminal branches of the right coronary artery. In one third of individuals it ends at the apex of the heart. The anterior interventricular branch supplies the right and left ventricles with numerous branches that also supply the anterior part of the ventricular septum. One of these ventricular branches (left diagonal artery) may arise directly from the trunk of the left coronary artery. A small left conus artery supplies the pulmonary conus.
  • The circumflex artery is the same size as the anteriorinterventricular artery (Fig. 3-42). It winds around the left margin of the heart in the atrioventricular groove. A left marginal artery is a large branch that supplies the left margin of the left ventricle down to the apex. Anterior ventricular and posterior ventricular branches supply the left ventricle. Atrial branches supply the left atrium.

Variations in the Coronary Arteries Variations in the blood supply to the heart do occur, and the most common variations affect the blood supply to the diaphragmatic surface of both ventricles. Here the origin, size, and distribution of the posterior interventricular artery are variable (Fig. 3-43). In right dominance, the posterior interventricular artery is a large branch of the right coronary artery. Right dominance is present in most individuals (90%). In left dominance, the posterior interventricular P.114
artery is a branch of the circumflex branch of the left coronary artery (10%).

Figure 3-42 Coronary arteries and veins.

Coronary Artery Anastomoses Anastomoses between the terminal branches of the right and left coronary arteries (collateral circulation) exist, but they are usually not large enough to provide an adequate blood supply to the cardiac muscle should one of the large branches become blocked by disease. A sudden block of one of the larger branches of either coronary artery usually leads to myocardial death (myocardial infarction), although sometimes the collateral circulation is enough to sustain the muscle. Summary of the Overall Arterial Supply to the Heart in Most Individuals The right coronary artery supplies all of the right ventricle (except for the small area to the right of the anterior interventricular groove), the variable part of the diaphragmatic surface of the left ventricle, the posteroinferior third of the ventricular septum, the right atrium and part of the left atrium, and the sinuatrial node and the atrioventricular node and bundle. The LBB also receives small branches. The left coronary artery supplies most of the left ventricle, a small area of the right ventricle to the right of the interventricular groove, the anterior two thirds of the ventricular septum, most of the left atrium, the RBB, and the LBB. Arterial Supply to the Conducting System The sinuatrial node is usually supplied by the right but sometimes by the left coronary artery. The atrioventricular node and the atrioventricular bundle are supplied by the right coronary artery. The RBB of the atrioventricular bundle is supplied by the left coronary artery; the LBB is supplied by the right and left coronary arteries (Fig. 3-43). P.115

Figure 3-43 A. Posterior view of the heart showing the origin and distribution of the posterior interventricular artery in the right dominance. B. Posterior view of the heart showing the origin and distribution of the posterior interventricular artery in the left dominance. C. Anterior view of the heart showing the relationship of the blood supply to the conducting system.

Clinical Notes Coronary Artery Disease The myocardium receives its blood supply through the right and left coronary arteries. Although the coronary arteries have numerous anastomoses at the arteriolar level, they are essentially functional end arteries. A sudden block of one of the large branches of either coronary artery will usually lead to necrosis of the cardiac muscle (myocardial infarction) in that vascular area, and often the patient dies. Most cases of coronary artery blockage are caused by an acute thrombosis on top of a chronic atherosclerotic narrowing of the lumen. Arteriosclerotic disease of the coronary arteries may present in three ways, depending on the rate of narrowing of the lumina of the arteries: (1) General degeneration and fibrosis of the myocardium occur over many years and are caused by a gradual narrowing of the coronary arteries. (2) Angina pectoris is cardiac pain that occurs on exertion and is relieved by rest. In this condition, the coronary arteries are so narrowed that myocardial ischemia occurs on exertion but not at rest. (3) Myocardial infarction occurs when coronary flow is suddenly reduced or stopped and the cardiac muscle undergoes necrosis. Myocardial infarction is the major cause of death in industrialized nations. Table 3-1 shows the different coronary arteries that supply the different areas of the myocardium. This information can be helpful when attempting to correlate the site of myocardial infarction, the artery involved, and the electrocardiographic signature. Because coronary bypass surgery, coronary angioplasty, and coronary artery stenting are now commonly accepted methods of treating coronary artery disease, it is incumbent on the student to be prepared to interpret still- and motion-picture angiograms that have been carried out before treatment. For this reason, a working knowledge of the origin, course, and distribution of the coronary arteries should be memorized. P.116

Table 3-1 Coronary Artery Lesions, Infarct Location, and ECG Signature
Coronary Artery Infarct Location ECG Signature
Proximal LAD Large anterior wall ST elevation: I, L, V1–V6
More distal LAD Anteroapical ST elevation: V2–V4
  Inferior wall if wraparound LAD ST elevation: II, III, F
Distal LAD Anteroseptal ST elevation: V1–V3
Early obtuse, marginal High lateral wall ST elevation: I, L, V4–V6
More distal marginal branch, circumflex Small lateral wall ST elevation: I, L, or V4–V6, or no abnormality
Circumflex Posterolateral ST elevation: V4–V6; ST depression: V1–V2
Distal RCA Small inferior wall ST elevation: II, III, F; ST depression: I, L
Proximal RCA Large inferior wall and posterior wall
Some lateral wall
ST elevation: II, III, F; ST depression: I, L, V1–V3
ST elevation: V5–V6
RCA Right ventricular ST elevation: V2R–V4R; some ST elevation: V1; or ST depression: V2, V3
  Usually inferior ST elevation: II, III, F
ECG, electrocardiographic; LAD, left anterior descending (interventricular); RCA, right coronary artery.

Venous Drainage of the Heart Most blood from the heart wall drains into the right atrium through the coronary sinus (Fig. 3-42), which lies in the posterior part of the atrioventricular groove and is a continuation of the great cardiac vein. It opens into the right atrium to the left of the inferior vena cava. The small and middle cardiac veins are tributaries of the coronary sinus. The remainder of the blood is returned to the right atrium by the anterior cardiac vein (Fig. 3-42) and by small veins that open directly into the heart chambers. Nerve Supply of the Heart The heart is innervated by sympathetic and parasympathetic fibers of the autonomic nervous system via the cardiac plexuses situated below the arch of the aorta. The sympathetic supply arises from the cervical and upper thoracic portions of the sympathetic trunks, and the parasympathetic supply comes from the vagus nerves. The postganglionic sympathetic fibers terminate on the sinuatrial and atrioventricular nodes, on cardiac muscle fibers, and on the coronary arteries. Activation of these nerves results in cardiac acceleration, increased force of contraction of the cardiac muscle, and dilatation of the coronary arteries. The postganglionic parasympathetic fibers terminate on the sinuatrial and atrioventricular nodes and on the coronary arteries. Activation of the parasympathetic nerves results in a reduction in the rate and force of contraction of the heart and a constriction of the coronary arteries. Afferent fibers running with the sympathetic nerves carry nervous impulses that normally do not reach consciousness. However, should the blood supply to the myocardium become impaired, pain impulses reach consciousness via this pathway. Afferent fibers running with the vagus nerves take part in cardiovascular reflexes. Clinical Notes Cardiac Pain Pain originating in the heart as the result of acute myocardial ischemia is assumed to be caused by oxygen deficiency and the accumulation of metabolites, which stimulate the sensory nerve endings in the myocardium. The afferent nerve fibers ascend to the central nervous system through the cardiac branches of the sympathetic trunk and enter the spinal cord through the posterior roots of the upper four thoracic nerves. The nature of the pain varies considerably, from a severe crushing pain to nothing more than a mild discomfort. The pain is not felt in the heart, but is referred to the skin areas supplied by the corresponding spinal nerves. The skin areas supplied by the upper four intercostal nerves and by the intercostobrachial nerve (T2) are therefore affected. The intercostobrachial nerve communicates with the medial cutaneous nerve of the arm and is distributed to skin on the medial side of the upper part of the arm. A certain amount of spread of nervous information must occur within the central nervous system, for the pain is sometimes felt in the neck and the jaw. Myocardial infarction involving the inferior wall or diaphragmatic surface of the heart often gives rise to discomfort in the epigastrium. One must assume that the afferent pain fibers from the heart ascend in the sympathetic nerves and enter the spinal cord in the posterior roots of the seventh, eighth, and ninth thoracic spinal nerves and give rise to referred pain in the T7, T8, and T9 thoracic dermatomes in the epigastrium. Because the heart and the thoracic part of the esophagus probably have similar afferent pain pathways, it is not surprising that painful acute esophagitis can mimic the pain of myocardial infarction. P.117
Action of the Heart The heart is a muscular pump. The series of changes that take place within it as it fills with blood and empties is referred to as the cardiac cycle. The normal heart beats 70 to 90 times per minute in the resting adult and 130 to 150 times per minute in the newborn child. Blood is continuously returning to the heart; during ventricular systole (contraction), when the atrioventricular valves are closed, the blood is temporarily accommodated in the large veins and atria. Once ventricular diastole (relaxation) occurs, the atrioventricular valves open, and blood passively flows from the atria to the ventricles (Fig. 3-39). When the ventricles are nearly full, atrial systole occurs and forces the remainder of the blood in the atria into the ventricles. The sinuatrial node initiates the wave of contraction in the atria, which commences around the openings of the large veins and milks the blood toward the ventricles. By this means, blood does not reflux into the veins. The cardiac impulse, having reached the atrioventricular node, is conducted to the papillary muscles by the atrioventricular bundle and its branches (Fig. 3-39). The papillary muscles then begin to contract and take up the slack of the chordae tendineae. Meanwhile, the ventricles start contracting and the atrioventricular valves close. The spread of the cardiac impulse along the atrioventricular bundle (Fig. 3-39) and its terminal branches, including the Purkinje fibers, ensures that myocardial contraction occurs at almost the same time throughout the ventricles. Once the intraventricular blood pressure exceeds that present in the large arteries (aorta and pulmonary trunk), the semilunar valve cusps are pushed aside, and the blood is ejected from the heart. At the conclusion of ventricular systole, blood begins to move back toward the ventricles and immediately fills the pockets of the semilunar valves. The cusps float into apposition and completely close the aortic and pulmonary orifices. Surface Anatomy of the Heart Valves The surface projection of the heart was described on page 72. The surface markings of the heart valves are as follows (Fig. 3-15):

  • The tricuspid valve lies behind the right half of the sternum opposite the fourth intercostal space.
  • The mitral valve lies behind the left half of the sternum opposite the fourth costal cartilage.
  • The pulmonary valve lies behind the medial end of the third left costal cartilage and the adjoining part of the sternum.
  • The aortic valve lies behind the left half of the sternum opposite the third intercostal space.

Clinical Notes Auscultation of the Heart Valves On listening to the heart with a stethoscope, one can hear two sounds: lūb-dūp. The first sound is produced by the contraction of the ventricles and the closure of the tricuspid and mitral valves. The second sound is produced by the sharp closure of the aortic and pulmonary valves. It is important for a physician to know where to place the stethoscope on the chest wall so that he or she will be able to hear sounds produced at each valve with the minimum of distraction or interference.

  • The tricuspid valve is best heard over the right half of the lower end of the body of the sternum (Fig. 3-15).
  • The mitral valve is best heard over the apex beat, that is, at the level of the fifth left intercostal space, 3.5 in. (9 cm) from the midline (Fig. 3-15).
  • The pulmonary valve is heard with least interference over the medial end of the second left intercostal space (Fig. 3-15).
  • The aortic valve is best heard over the medial end of the second right intercostal space (Fig. 3-15).

Valvular Disease of the Heart Inflammation of a valve can cause the edges of the valve cusps to stick together. Later, fibrous thickening occurs, followed by loss of flexibility and shrinkage. Narrowing (stenosis) and valvular incompetence (regurgitation) result, and the heart ceases to function as an efficient pump. In rheumatic disease of the mitral valve, for example, not only do the cusps undergo fibrosis and shrink, but also the chordae tendineae shorten, preventing closure of the cusps during ventricular systole. Valvular Heart Murmurs Apart from the sounds of the valves closing, lūb-dūp, the blood passes through the normal heart silently. Should the valve orifices become narrowed or the valve cusps distorted and shrunken by disease, however, a rippling effect would be set up, leading to turbulence and vibrations that are heard as heart murmurs. Traumatic Asphyxia The sudden caving in of the anterior chest wall associated with fractures of the sternum and ribs causes a dramatic rise in intrathoracic pressure. Apart from the immediate evidence of respiratory distress, the anatomy of the venous system plays a significant role in the production of the characteristic vascular signs of traumatic asphyxia. The thinness of the walls of the thoracic veins and the right atrium causes their collapse under the raised intrathoracic pressure, and venous blood is dammed back in the veins of the neck and head. This produces venous congestion; bulging of the eyes, which become injected; and swelling of the lips and tongue, which become cyanotic. The skin of the face, neck, and shoulders becomes purple. The Anatomy of Cardiopulmonary Resuscitation Cardiopulmonary resuscitation (CPR), achieved by compression of the chest, was originally believed to succeed because of the compression of the heart between the sternum and the vertebral column. Now it is recognized that the blood flows in CPR because the whole thoracic cage is the pump; the heart functions merely as a conduit for blood. An extrathoracic pressure gradient is created by external chest compressions. The pressure in all chambers and locations within the chest cavity is the same. With compression, blood is forced out of the thoracic cage. The blood preferentially flows out the arterial side of the circulation and back down the venous side because the venous valves in the internal jugular system prevent a useless oscillatory movement. With the release of compression, blood enters the thoracic cage, preferentially down the venous side of the systemic circulation. Embryologic Notes Development of the Heart Formation of the Heart Tube Clusters of cells arise in the mesenchyme at the cephalic end of the embryonic disc, cephalic to the site of the developing mouth and the nervous system. These clusters of cells form a plexus of endothelial blood vessels that fuse to form the right and left endocardial heart tubes. These, too, soon fuse to form a single median endocardial tube. As the head fold of the embryo develops, the endocardial tube and the pericardial cavity rotate on a transverse axis through almost 180°, so that they come to lie ventral to (in front of) the esophagus and caudal to the developing mouth. The heart tube starts to bulge into the pericardial cavity (Fig. 3-44). Meanwhile, the endocardial tube becomes surrounded by a thick layer of mesenchyme, which will differentiate into the myocardium and the visceral layer of the serous pericardium. The primitive heart has been established, and the cephalic end is the arterial end and the caudal end is the venous end. The arterial end of the primitive heart is continuous beyond the pericardium with a large vessel, the aortic sac (Fig. 3-45). The heart begins to beat during the third week. Further Development of the Heart Tube The heart tube then undergoes differential expansion so that several dilatations, separated by grooves, result. From the arterial to the venous end, these dilatations are called the bulbus cordis, the ventricle, the atrium, and the right and left horns of the sinus venosus. The bulbus cordis and ventricular parts of the tube now elongate more rapidly than the remainder of the tube, and since the arterial and venous ends are fixed by the pericardium, the tube begins to bend (Fig. 3-46). The bend soon becomes U-shaped and then forms a compound S-shape, with the atrium lying posterior to the ventricle; thus, the venous and arterial ends are brought close together as they are in the adult. The passage between the atrium and the ventricle narrows to form the atrioventricular canal. As these changes are taking place, a gradual migration of the heart tube occurs so that the heart passes from the neck region to what will become the thoracic region. Development of the Atria The primitive atrium becomes divided into two—the right and left atria—in the following manner (Fig. 3-47). First, the atrioventricular canal widens transversely. The canal then becomes divided into right and left halves by the appearance of ventral and dorsal atrioventricular cushions, which fuse to form the septum intermedium. Meanwhile, another septum, the septum primum, develops from the roof of the primitive atrium and grows down to fuse with the septum intermedium. Before fusion occurs, the opening between the lower edge of the septum primum and septum intermedium is referred to as the foramen primum. The atrium now is divided into right and left parts. Before complete obliteration of the foramen primum has taken place, degenerative changes occur in the central portion of the septum primum; a foramen appears, the foramen secundum, so that the right and left atrial chambers again communicate. Another, thicker, septum (the septum secundum) grows down from the atrial roof on the right side of the septum primum. The lower edge of the septum secundum overlaps the foramen secundum in the septum primum but does not reach the floor of the atrium and does not fuse with the septum intermedium. The space between the free margin of the septum secundum and the septum primum is now known as the foramen ovale (Fig. 3-47). Before birth, the foramen ovale allows oxygenated blood that has entered the right atrium from the inferior vena cava to pass into the left atrium. However, the lower part of the septum primum serves as a flaplike valve to prevent blood from moving from the left atrium into the right atrium. At birth, owing to raised blood pressure in the left atrium, the septum primum is pressed against the septum secundum and fuses with it, and the foramen ovale is closed. The two atria thus are separated from each other. The lower edge of the septum secundum seen in the right atrium becomes the anulus ovalis, and the depression below this is called the fossa ovalis. The right and left auricular appendages later develop as small diverticula from the right and left atria, respectively. Development of the Ventricles A muscular partition projects upward from the floor of the primitive ventricle to form the ventricular septum (Fig. 3-47). The space bounded by the crescentic upper edge of the septum and the endocardial cushions forms the interventricular foramen. Meanwhile, spiral subendocardial thickenings, the bulbar ridges, appear in the distal part of the bulbus cordis. The bulbar ridges then grow and fuse to form a spiral aorticopulmonary septum (Fig. 3-48). The interventricular foramen closes as the result of proliferation of the bulbar ridges and the fused endocardial cushions (septum intermedium). This newly formed tissue grows down and fuses with the upper edge of the muscular ventricular septum to form the membranous part of the septum (Fig. 3-47). The closure of the interventricular foramen not only shuts off the path of communication between the right and left ventricles, but also ensures that the right ventricular cavity communicates with the pulmonary trunk and the left ventricular cavity communicates with the aorta. In addition, the right atrioventricular opening now connects exclusively with the right ventricular cavity and the left atrioventricular opening, with the left ventricular cavity.

Figure 3-44 The development of the endocardial tube in relation to the pericardial cavity.

Development of the Roots and Proximal Portions of the Aorta and Pulmonary Trunk The distal part of the bulbus cordis is known as the truncus arteriosus (Fig. 3-45). It is divided by the spiral aorticopulmonary septum to form the roots and proximal portions of the aorta and pulmonary trunk (Fig. 3-48). With the establishment of right and left ventricles, the proximal portion of the bulbus cordis becomes incorporated into the right ventricle as the definitive conus arteriosus or infundibulum, and into the left ventricle as the aortic vestibule. Just distal to the aortic valves, the two coronary arteries arise as outgrowths from the developing aorta. Development of the Cardiac Valves Semilunar Valves of the Aorta and Pulmonary Arteries After the formation of the aorticopulmonary septum, three swellings appear at the orifices of both the aorta and the pulmonary artery. Each swelling consists of a covering of endothelium over loose connective tissue. Gradually, the swellings become excavated on their upper surfaces to form the semilunar valves.

Figure 3-45 The parts of the endocardial heart tube within the pericardium.
Figure 3-46 The bending of the heart tube within the pericardial cavity. The interior of the developing ventricles is shown at the bottom right.
Figure 3-47 The division of the primitive atrium into the right and left atria by the appearance of the septa. The sinuatrial orifice and the fate of the venous valves are shown, as is the appearance of the ventricular septum.

Atrioventricular Valves After the formation of the septum intermedium, the atrioventricular canal becomes divided into right and left atrioventricular orifices. Raised folds of endocardium appear at the margins of these orifices. These folds are invaded by mesenchymal tissue that later becomes hollowed out from the ventricular side. Three valvular cusps are formed about the right atrioventricular orifice and constitute the tricuspid valve; two cusps are formed about the left atrioventricular orifice to become the mitral valve. The newly formed cusps enlarge, and their mesenchymal core becomes differentiated into fibrous tissue. The cusps remain attached at intervals to the ventricular wall by muscular strands. Later, the muscular strands become differentiated into papillary muscles and chordae tendineae.

Figure 3-48 The division of the bulbus cordis by the spiral aorticopulmonary septum into the aorta and pulmonary trunk. A. The spiral septum in the truncus arteriosus (upper part of the bulbus cordis). B. The lower part of the bulbus cordis showing the formation of the spiral septum by fusion of the bulbar ridges (red), which then grow down and join the septum intermedium (blue) and the muscular part of the ventricular septum. C. The area of the ventricular septum that is formed from the fused bulbar ridges (red) and the septum intermedium (blue) is called the membranous part of the ventricular septum.

Congenital Anomalies of the Heart Atrial Septal Defects After birth, the foramen ovale becomes completely closed as the result of the fusion of the septum primum with the septum secundum. In 25% of hearts, a small opening persists, but this is usually of such a minor nature that it has no clinical significance. Occasionally, the opening is much larger and results in oxygenated blood from the left atrium passing over into the right atrium (Fig. 3-38). Ventricular Septal Defects The ventricular septum is formed in a complicated manner and is complete only when the membranous part fuses with the muscular part. Ventricular septal defects are less frequent than atrial septal defects. They are found in the membranous part of the septum and can measure 1 to 2 cm in diameter. Blood under high pressure passes through the defect from left to right, causing enlargement of the right ventricle. Large defects are serious and can shorten life if surgery is not performed. Tetralogy of Fallot Normally, the bulbus cordis becomes divided into the aorta and pulmonary trunk by the formation of the spiral aorticopulmonary septum. This septum is formed by the fusion of the bulbar ridges. If the bulbar ridges fail to fuse correctly, unequal division of the bulbus cordis may occur, with consequent narrowing of the pulmonary trunk resulting in interference with the right ventricular outflow. This congenital anomaly is responsible for about 9% of all congenital heart disease (Fig. 3-38). The anatomic abnormalities include large ventricular septal defect; stenosis of the pulmonary trunk, which can occur at the infundibulum of the right ventricle or at the pulmonary valve; exit of the aorta immediately above the ventricular septal defect (instead of from the left ventricular cavity only); and severe hypertrophy of the right ventricle, because of the high blood pressure in the right ventricle. The defects cause congenital cyanosis and considerably limit activity; patients with severe untreated abnormalities die. Once the diagnosis has been made, most children can be successfully treated surgically. Most children find that assuming the squatting position after physical activity relieves their breathlessness. This happens because squatting reduces the venous return by compressing the abdominal veins and increasing the systemic arterial resistance by kinking the femoral and popliteal arteries in the legs; both these mechanisms tend to decrease the right to left shunt through the ventricular septal defect and improve the pulmonary circulation. P.118
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Large Veins of the Thorax Brachiocephalic Veins The right brachiocephalic vein is formed at the root of the neck by the union of the right subclavian and the right internal jugular veins (Figs. 3-16 and 3-49). The left brachiocephalic vein has a similar origin (Figs. 3-31 and 3-33). It passes obliquely downward and to the right behind the manubrium sterni and in front of the large branches of the aortic arch. It joins the right brachiocephalic vein to form the superior vena cava (Fig. 3-49). Superior Vena Cava The superior vena cava contains all the venous blood from the head and neck and both upper limbs and is formed by the union of the two brachiocephalic veins (Figs. 3-33 and 3-49). It passes downward to end in the right atrium of the heart (Fig. 3-30). The vena azygos joins the posterior aspect of the superior vena cava just before it enters the pericardium (Figs. 3-16 and 3-49). Azygos Veins The azygos veins consist of the main azygos vein, the inferior hemiazygos vein, and the superior hemiazygos vein. They drain blood from the posterior parts of the intercostal spaces, the posterior abdominal wall, the pericardium, the diaphragm, the bronchi, and the esophagus (Fig. 3-49). Azygos Vein The origin of the azygos vein is variable. It is often formed by the union of the right ascending lumbar vein and the right subcostal vein. It ascends through the aortic opening in the diaphragm on the right side of the aorta to the level of the fifth thoracic vertebra (Fig. 3-49). Here it arches forward above the root of the right lung to empty into the posterior surface of the superior vena cava (Fig. 3-16). The azygos vein has numerous tributaries, including the eight lower right intercostal veins, the right superior intercostal vein, the superior and inferior hemiazygos veins, and numerous mediastinal veins. Inferior Hemiazygos Vein The inferior hemiazygos vein is often formed by the union of the left ascending lumbar vein and the left subcostal vein. It ascends through the left crus of the diaphragm and, at about the level of the eighth thoracic vertebra, turns to the right and joins the azygos vein (see Fig. 2-11). It receives as tributaries some lower left intercostal veins and mediastinal veins. Superior Hemiazygos Vein The superior hemiazygos vein is formed by the union of the fourth to the eighth intercostal veins. It joins the azygos vein at the level of the seventh thoracic vertebra (see Fig. 2-11). Inferior Vena Cava The inferior vena cava pierces the central tendon of the diaphragm opposite the eighth thoracic vertebra and almost immediately enters the lowest part of the right atrium (Figs. 3-16, 3-37, and 3-49). Clinical Notes Azygos Veins and Caval Obstruction In obstruction of the superior or inferior venae cavae, the azygos veins provide an alternative pathway for the return of venous blood to the right atrium of the heart. This is possible because these veins and their tributaries connect the superior and inferior venae cavae. Pulmonary Veins Two pulmonary veins leave each lung carrying oxygenated blood to the left atrium of the heart (Figs. 3-16, 3-36, and 3-40). Large Arteries of the Thorax Aorta The aorta is the main arterial trunk that delivers oxygenated blood from the left ventricle of the heart to the tissues of the P.124
body. It is divided for purposes of description into the following parts: ascending aorta, arch of the aorta, descending thoracic aorta, and abdominal aorta.

Figure 3-49 A. Major veins entering the heart. B. Major veins draining into the superior and inferior venae cavae.

Ascending Aorta The ascending aorta begins at the base of the left ventricle and runs upward and forward to come to lie behind the right half of the sternum at the level of the sternal angle, where it becomes continuous with the arch of the aorta (Fig. 3-35). The ascending aorta lies within the fibrous pericardium (Fig. 3-33) and is enclosed with the pulmonary trunk in a sheath of serous pericardium. At its root it possesses three bulges, the sinuses of the aorta, one behind each aortic valve cusp. Branches The right coronary artery arises from the anterior aortic sinus, and the left coronary artery arises from the left P.125
posterior aortic sinus (Figs. 3-35 and 3-42). The further course of these important arteries is described on pages 113 to 114. Arch of the Aorta The arch of the aorta is a continuation of the ascending aorta (Fig. 3-35). It lies behind the manubrium sterni and arches upward, backward, and to the left in front of the trachea (its main direction is backward). It then passes downward to the left of the trachea and, at the level of the sternal angle, becomes continuous with the descending aorta. Branches The brachiocephalic artery arises from the convex surface of the aortic arch (Figs. 3-35 and 3-50). It passes upward and to the right of the trachea and divides into the right subclavian and right common carotid arteries behind the right sternoclavicular joint.

Figure 3-50 Major branches of the aorta.

The left common carotid artery arises from the convex surface of the aortic arch on the left side of the brachiocephalic artery (Figs. 3-35 and 3-50). It runs upward and to the left of the trachea and enters the neck behind the left sternoclavicular joint. The left subclavian artery arises from the aortic arch behind the left common carotid artery (Figs. 3-35, 3-36, and 3-50). It runs upward along the left side of the trachea and the esophagus to enter the root of the neck (Fig. 3-16). It arches over the apex of the left lung. Descending Thoracic Aorta The descending thoracic aorta lies in the posterior mediastinum and begins as a continuation of the arch of the aorta on the left side of the lower border of the body of the fourth thoracic vertebra (i.e., opposite the sternal angle). It runs downward in the posterior mediastinum, inclining forward and medially to reach the anterior surface of the vertebral column (Figs. 3-16 and 3-50). At the level of the 12th P.126
thoracic vertebra, it passes behind the diaphragm (through the aortic opening) in the midline and becomes continuous with the abdominal aorta. Branches Posterior intercostal arteries are given off to the lower nine intercostal spaces on each side (Fig. 3-50). Subcostal arteries are given off on each side and run along the lower border of the 12th rib to enter the abdominal wall. Pericardial, esophageal, and bronchial arteries are small branches that are distributed to these organs. Clinical Notes Aneurysm and Coarctation of the Aorta The arch of the aorta lies behind the manubrium sterni. A gross dilatation of the aorta (aneurysm) may show itself as a pulsatile swelling in the suprasternal notch. Coarctation of the aorta is a congenital narrowing of the aorta just proximal, opposite, or distal to the site of attachment of the ligamentum arteriosum. This condition is believed to result from an unusual quantity of ductus arteriosus muscle tissue in the wall of the aorta. When the ductus arteriosus contracts, the ductal muscle in the aortic wall also contracts, and the aortic lumen becomes narrowed. Later, when fibrosis takes place, the aortic wall also is involved, and permanent narrowing occurs. Clinically, the cardinal sign of aortic coarctation is absent or diminished pulses in the femoral arteries of both lower limbs. To compensate for the diminished volume of blood reaching the lower part of the body, an enormous collateral circulation develops, with dilatation of the internal thoracic, subclavian, and posterior intercostal arteries. The dilated intercostal arteries erode the lower borders of the ribs, producing characteristic notching, which is seen on radiographic examination. The condition should be treated surgically. Pulmonary Trunk The pulmonary trunk conveys deoxygenated blood from the right ventricle of the heart to the lungs. It leaves the upper part of the right ventricle and runs upward, backward, and to the left (Fig. 3-35). It is about 2 in. (5 cm) long and terminates in the concavity of the aortic arch by dividing into right and left pulmonary arteries (Fig. 3-12). Together with the ascending aorta, it is enclosed in the fibrous pericardium and a sheath of serous pericardium (Fig. 3-33). Branches The right pulmonary artery runs to the right behind the ascending aorta and superior vena cava to enter the root of the right lung (Figs. 3-12, 3-16, and 3-35). The left pulmonary artery runs to the left in front of the descending aorta to enter the root of the left lung (Figs. 3-12, 3-16, and 3-35). The ligamentum arteriosum is a fibrous band that connects the bifurcation of the pulmonary trunk to the lower concave surface of the aortic arch (Figs. 3-16 and 3-36). The ligamentum arteriosum is the remains of the ductus arteriosus, which in the fetus conducts blood from the pulmonary trunk to the aorta, thus bypassing the lungs. The left recurrent laryngeal nerve hooks around the lower border of this structure (Figs. 3-16 and 3-36). After birth, the ductus closes. Should it remain patent, aortic blood will enter the pulmonary circulation, producing pulmonary hypertension and hypertrophy of the right ventricle (Fig. 3-38). Surgical ligation of the ductus is then necessary. Clinical Notes Patent Ductus Arteriosus The ductus arteriosus represents the distal portion of the sixth left aortic arch and connects the left pulmonary artery to the beginning of the descending aorta (Fig. 3-38D). During fetal life, blood passes through it from the pulmonary artery to the aorta, thus bypassing the lungs. After birth, it normally constricts, later closes, and becomes the ligamentum arteriosum. Failure of the ductus arteriosus to close may occur as an isolated congenital abnormality or may be associated with congenital heart disease. A persistent patent ductus arteriosus results in high-pressure aortic blood passing into the pulmonary artery, which raises the pressure in the pulmonary circulation. A patent ductus arteriosus is life threatening and should be ligated and divided surgically. Lymph Nodes and Vessels of the Thorax Thoracic Wall The lymph vessels of the skin of the anterior thoracic wall drain to the anterior axillary nodes. The lymph vessels of the skin of the posterior thoracic wall drain to the posterior axillary nodes. The deep lymph vessels of the anterior parts of the intercostal spaces drain forward to the internal thoracic nodes along the internal thoracic blood vessels. From here, the lymph passes to the thoracic duct on the left side and the bronchomediastinal trunk on the right side. The deep lymph vessels of the posterior parts of the intercostal spaces drain backward to the posterior intercostal nodes lying near the heads of the ribs. From here, the lymph enters the thoracic duct. Mediastinum In addition to the nodes draining the lungs, other nodes are found scattered through the mediastinum. They drain lymph from mediastinal structures and empty into the bronchomediastinal trunks and thoracic duct. Disease and enlargement of these nodes may exert pressure on important neighboring mediastinal structures, such as the trachea and superior vena cava. Thoracic Duct The thoracic duct begins below in the abdomen as a dilated sac, the cisterna chyli. It ascends through the aortic opening in the diaphragm, on the right side of the descending P.127
aorta. It gradually crosses the median plane behind the esophagus and reaches the left border of the esophagus (Fig. 3-6B) at the level of the lower border of the body of the fourth thoracic vertebra (sternal angle). It then runs upward along the left edge of the esophagus to enter the root of the neck (Fig. 3-6B). Here, it bends laterally behind the carotid sheath and in front of the vertebral vessels. It turns downward in front of the left phrenic nerve and crosses the subclavian artery to enter the beginning of the left brachiocephalic vein. At the root of the neck, the thoracic duct receives the left jugular, subclavian, and bronchomediastinal lymph trunks, although they may drain directly into the adjacent large veins. The thoracic duct thus conveys to the blood all lymph from the lower limbs, pelvic cavity, abdominal cavity, left side of the thorax, and left side of the head, neck, and left arm (see Fig 1-21). Right Lymphatic Duct The right jugular, subclavian, and bronchomediastinal trunks, which drain the right side of the head and neck, the right upper limb, and the right side of the thorax, respectively, may join to form the right lymphatic duct. This common duct, if present, is about 0.5 in. (1.3 cm) long and opens into the beginning of the right brachiocephalic vein. Alternatively, the trunks open independently into the great veins at the root of the neck. Nerves of the Thorax Vagus Nerves The right vagus nerve descends in the thorax, first lying posterolateral to the brachiocephalic artery (Fig. 3-6), then lateral to the trachea and medial to the terminal part of the azygos vein (Fig. 3-16). It passes behind the root of the right lung and assists in the formation of the pulmonary plexus. On leaving the plexus, the vagus passes onto the posterior surface of the esophagus and takes part in the formation of the esophageal plexus. It then passes through the esophageal opening of the diaphragm behind the esophagus to reach the posterior surface of the stomach. The left vagus nerve descends in the thorax between the left common carotid and the left subclavian arteries (Figs. 3-6 and 3-16). It then crosses the left side of the aortic arch and is itself crossed by the left phrenic nerve. The vagus then turns backward behind the root of the left lung and assists in the formation of the pulmonary plexus. On leaving the plexus, the vagus passes onto the anterior surface of the esophagus and takes part in the formation of the esophageal plexus. It then passes through the esophageal opening in the diaphragm in front of the esophagus to reach the anterior surface of the stomach. Branches Both vagi supply the lungs and esophagus. The right vagus gives off cardiac branches, and the left vagus gives origin to the left recurrent laryngeal nerve. (The right recurrent laryngeal nerve arises from the right vagus in the neck and hooks around the subclavian artery and ascends between the trachea and esophagus.) The left recurrent laryngeal nerve arises from the left vagus trunk as the nerve crosses the arch of the aorta (Figs. 3-16 and 3-36). It hooks around the ligamentum arteriosum and ascends in the groove between the trachea and the esophagus on the left side (Fig. 3-6). It supplies all the muscles acting on the left vocal cord (except the cricothyroid muscle, a tensor of the cord, which is supplied by the external laryngeal branch of the vagus). Phrenic Nerves The phrenic nerves arise from the neck from the anterior rami of the third, fourth, and fifth cervical nerves (see page 771). The right phrenic nerve descends in the thorax along the right side of the right brachiocephalic vein and the superior vena cava (Figs. 3-6 and 3-16). It passes in front of the root of the right lung and runs along the right side of the pericardium, which separates the nerve from the right atrium. It then descends on the right side of the inferior vena cava to the diaphragm. Its terminal branches pass through the caval opening in the diaphragm to supply the central part of the peritoneum on its underaspect. The left phrenic nerve descends in the thorax along the left side of the left subclavian artery. It crosses the left side of the aortic arch (Fig. 3-16) and here crosses the left side of the left vagus nerve. It passes in front of the root of the left lung and then descends over the left surface of the pericardium, which separates the nerve from the left ventricle. On reaching the diaphragm, the terminal branches pierce the muscle and supply the central part of the peritoneum on its underaspect. The phrenic nerves possess efferent and afferent fibers. The efferent fibers are the sole nerve supply to the muscle of the diaphragm. The afferent fibers carry sensation to the central nervous system from the peritoneum covering the central region of the undersurface of the diaphragm, the pleura covering the central region of the upper surface of the diaphragm, and the pericardium and mediastinal parietal pleura. Clinical Notes Paralysis of the Diaphragm The phrenic nerve may be paralyzed because of pressure from malignant tumors in the mediastinum. Surgical crushing or sectioning of the phrenic nerve in the neck, producing paralysis of the diaphragm on one side, was once used as part of the treatment of lung tuberculosis, especially of the lower lobes. The immobile dome of the diaphragm rests the lung. Thoracic Part of the Sympathetic Trunk The thoracic part of the sympathetic trunk is continuous above with the cervical and below with the lumbar parts of the sympathetic trunk. It is the most laterally placed structure P.128
in the mediastinum and runs downward on the heads of the ribs (Fig. 3-16). It leaves the thorax on the side of the body of the 12th thoracic vertebra by passing behind the medial arcuate ligament. The sympathetic trunk has 12 (often only 11) segmentally arranged ganglia, each with white and gray ramus communicans passing to the corresponding spinal nerve. The first ganglion is often fused with the inferior cervical ganglion to form the stellate ganglion. Branches

  • Gray rami communicantes go to all the thoracic spinal nerves. The postganglionic fibers are distributed through the branches of the spinal nerves to the blood vessels, sweat glands, and arrector pili muscles of the skin.
  • The first five ganglia give postganglionic fibers to the heart, aorta, lungs, and esophagus.
  • The lower eight ganglia mainly give preganglionic fibers, which are grouped together to form the splanchnic nerves (Fig. 3-16) and supply the abdominal viscera. They enter the abdomen by piercing the crura of the diaphragm. The greater splanchnic nerve arises from ganglia 5 to 9, the lesser splanchnic nerve arises from ganglia 10 and 11, and the lowest splanchnic nerve arises from ganglion 12. For details of the distribution of these nerves in the abdomen, see page 279.

Clinical Notes Sympathetic Trunk in the Treatment of Raynaud Disease Preganglionic sympathectomy of the second and third thoracic ganglia can be performed to increase the blood flow to the fingers for such conditions as Raynaud disease. The sympathectomy causes vasodilatation of the arterioles in the upper limb. Spinal Anesthesia and the Sympathetic Nervous System A high spinal anesthetic may block the preganglionic sympathetic fibers passing out from the lower thoracic segments of the spinal cord. This produces temporary vasodilatation below this level, with a consequent fall in blood pressure. Esophagus The esophagus is a tubular structure about 10 in. (25 cm) long that is continuous above with the laryngeal part of the pharynx opposite the sixth cervical vertebra. It passes through the diaphragm at the level of the 10th thoracic vertebra to join the stomach (Fig. 3-10). In the neck, the esophagus lies in front of the vertebral column; laterally, it is related to the lobes of the thyroid gland; and anteriorly, it is in contact with the trachea and the recurrent laryngeal nerves (see page 795). In the thorax, it passes downward and to the left through the superior and then the posterior mediastinum. At the level of the sternal angle, the aortic arch pushes the esophagus over to the midline (Fig. 3-6). The relations of the thoracic part of the esophagus from above downward are as follows:

  • Anteriorly: The trachea and the left recurrent laryngeal nerve; the left principal bronchus, which constricts it; and the pericardium, which separates the esophagus from the left atrium (Figs. 3-6 and 3-40)
  • Posteriorly: The bodies of the thoracic vertebrae; the thoracic duct; the azygos veins; the right posterior intercostal arteries; and, at its lower end, the descending thoracic aorta (Figs. 3-6 and 3-40)
  • Right side: The mediastinal pleura and the terminal part of the azygos vein (Fig. 3-16)
  • Left side: The left subclavian artery, the aortic arch, the thoracic duct, and the mediastinal pleura (Fig. 3-16)

Inferiorly to the level of the roots of the lungs, the vagus nerves leave the pulmonary plexus and join with sympathetic nerves to form the esophageal plexus. The left vagus lies anterior to the esophagus and the right vagus lies posterior. At the opening in the diaphragm, the esophagus is accompanied by the two vagi, branches of the left gastric blood vessels, and lymphatic vessels. Fibers from the right crus of the diaphragm pass around the esophagus in the form of a sling. In the abdomen, the esophagus descends for about 0.5 in. (1.3 cm) and then enters the stomach. It is related to the left lobe of the liver anteriorly and to the left crus of the diaphragm posteriorly. Blood Supply of the Esophagus The upper third of the esophagus is supplied by the inferior thyroid artery, the middle third by branches from the descending thoracic aorta, and the lower third by branches from the left gastric artery. The veins from the upper third drain into the inferior thyroid veins, from the middle third into the azygos veins, and from the lower third into the left gastric vein, a tributary of the portal vein. Lymph Drainage of the Esophagus Lymph vessels from the upper third of the esophagus drain into the deep cervical nodes, from the middle third into the superior and posterior mediastinal nodes, and from the lower third into nodes along the left gastric blood vessels and the celiac nodes (Fig. 3-27). Nerve Supply of the Esophagus The esophagus is supplied by parasympathetic and sympathetic efferent and afferent fibers via the vagi and sympathetic trunks. In the lower part of its thoracic course, the esophagus is surrounded by the esophageal nerve plexus. Clinical Notes Esophageal Constrictions The esophagus has three anatomic and physiologic constrictions. The first is where the pharynx joins the upper end, the second is where the aortic arch and the left bronchus cross its anterior surface, and the third occurs where the esophagus passes through the diaphragm into the stomach. These constrictions are of considerable clinical importance because they are sites where swallowed foreign bodies can lodge or through which it may be difficult to pass an esophagoscope. Because a slight delay in the passage of food or fluid occurs at these levels, strictures develop here after the drinking of caustic fluids. Those constrictions are also the common sites of carcinoma of the esophagus. It is useful to remember that their respective distances from the upper incisor teeth are 6 in. (15 cm), 10 in. (25 cm), and 16 in. (41 cm), respectively (Fig. 3-51). Portal–Systemic Venous Anastomosis At the lower third of the esophagus is an important portal–systemic venous anastomosis. (For other portal–systemic anastomoses, see page 246). Here, the esophageal tributaries of the azygos veins (systemic veins) anastomose with the esophageal tributaries of the left gastric vein (which drains into the portal vein). Should the portal vein become obstructed, as, for example, in cirrhosis of the liver, portal hypertension develops, resulting in the dilatation and varicosity of the portal–systemic anastomoses. Varicosed esophageal veins may rupture during the passage of food, causing hematemesis (vomiting of blood), which may be fatal. Carcinoma of the Lower Third of the Esophagus The lymph drainage of the lower third of the esophagus descends through the esophageal opening in the diaphragm and ends in the celiac nodes around the celiac artery (Fig. 3-27). A malignant tumor of this area of the esophagus would therefore tend to spread below the diaphragm along this route. Consequently, surgical removal of the lesion would include not only the primary lesion, but also the celiac lymph nodes and all regions that drain into these nodes, namely, the stomach, the upper half of the duodenum, the spleen, and the omenta. Restoration of continuity of the gut is accomplished by performing an esophagojejunostomy. The Esophagus and the Left Atrium of the Heart The close relationship between the anterior wall of the esophagus and the posterior wall of the left atrium has already been emphasized. A barium swallow may help a physician assess the size of the left atrium in cases of left-sided heart failure, in which the left atrium becomes distended because of back pressure of venous blood. P.129
Thymus The thymus is a flattened, bilobed structure (Fig. 3-6) lying between the sternum and the pericardium in the anterior mediastinum. In the newborn infant, it reaches its largest size relative to the size of the body, at which time it may extend up through the superior mediastinum in front of the great vessels into the root of the neck. The thymus continues to grow until puberty but thereafter undergoes involution. It has a pink, lobulated appearance and is the site for development of T (thymic) lymphocytes. Blood Supply The blood supply of the thymus is from the inferior thyroid and internal thoracic arteries. Clinical Notes Chest Pain The presenting symptom of chest pain is a common problem in clinical practice. Unfortunately, chest pain is a symptom common to many conditions and may be caused by disease in the thoracic and abdominal walls or in many different thoracic and abdominal viscera. The severity of the pain is often unrelated to the seriousness of the cause. Myocardial pain may mimic esophagitis, musculoskeletal chest wall pain, and other non–life-threatening causes. Unless the physician is astute, a patient may be discharged with a more serious condition than the symptoms indicate. It is not good enough to have a correct diagnosis only 99% of the time with chest pain. An understanding of chest pain helps the physician in the systematic consideration of the differential diagnosis. Somatic Chest Pain Pain arising from the chest or abdominal walls is intense and discretely localized. Somatic pain arises in sensory nerve endings in these structures and is conducted to the central nervous system by segmental spinal nerves. Visceral Chest Pain Visceral pain is diffuse and poorly localized. It is conducted to the central nervous system along afferent autonomic nerves. Most visceral pain fibers ascend to the spinal cord along sympathetic nerves and enter the cord through the posterior nerve roots of segmental spinal nerves. Some pain fibers from the pharynx and upper part of the esophagus and the trachea enter the central nervous system through the parasympathetic nerves via the glossopharyngeal and vagus nerves.

Figure 3-51 The approximate respective distances from the incisor teeth (black) and the nostrils (red) to the normal three constrictions of the esophagus. To assist in the passage of a tube to the duodenum, the distances to the first part of the duodenum are also included.

Referred Chest Pain Referred chest pain is the feeling of pain at a location other than the site of origin of the stimulus, but in an area supplied by the same or adjacent segments of the spinal cord. Both somatic and visceral structures can produce referred pain. Thoracic Dermatomes To understand chest pain, a working knowledge of the thoracic dermatomes is essential (see pages 27 and 28). Pain and Lung Disease For a full discussion, see page 103. Cardiac Pain For a full discussion, see page 116. P.130
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Cross-Sectional Anatomy of the Thorax To assist in the interpretation of CT scans of the thorax, study the labeled cross sections of the thorax shown in Figure 3-52. The sections have been photographed on their inferior surfaces (see Figs. 3-53 and 3-54 for CT scans). Radiographic Anatomy Only the more important features seen on standard posteroanterior and oblique lateral radiographs of the chest are discussed here. Posteroanterior Radiograph A posteroanterior radiograph is taken with the anterior wall of the patient’s chest touching the cassette holder and with the x-rays traversing the thorax from the posterior to the anterior aspect (Figs. 3-55 and 3-56). First check to make sure that the radiograph is a true posteroanterior radiograph and is not slightly oblique. Look at the sternal ends of both clavicles; they should be equidistant from the vertebral spines. Now examine the following in a systematic order:

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    the lung fields. The pectoralis major may also cast a soft shadow.
    Figure 3-52 Cross sections of the thorax viewed from below. A. At the level of the body of the third thoracic vertebra. B. At the level of the eighth thoracic vertebra. Note that in the living, the pleural cavity is only a potential space. The large space seen here is an artifact and results from the embalming process.
    Figure 3-53 Computed tomography scan of the upper part of the thorax at the level of the third thoracic vertebra. The section is viewed from below.
    Figure 3-54 Computed tomography scan of the middle part of the thorax at the level of the sixth thoracic vertebra. The section is viewed from below.
    Figure 3-55 Posteroanterior radiograph of the chest of a normal adult man.
  • Bones. The thoracic vertebrae are imperfectly seen. The costotransverse joints and each rib should be examined in order from above downward and compared to the fellows of the opposite side (Fig. 3-55). The costal cartilages are not usually seen, but if calcified, they will be visible. The clavicles are clearly seen crossing the upper part of each lung field. The medial borders of the scapulae may overlap the periphery of each lung field.
  • Diaphragm. The diaphragm casts dome-shaped shadows on each side; the one on the right is slightly higher than the one on the left. Note the costophrenic angle, where the diaphragm meets the thoracic wall (Fig. 3-55). Beneath the right dome is the homogeneous, dense shadow of the liver, and beneath the left dome a gas bubble may be seen in the fundus of the stomach.
  • Trachea. The radiotranslucent, air-filled shadow of the trachea is seen in the midline of the neck as a dark area (Fig. 3-55). This is superimposed on the lower cervical and upper thoracic vertebrae.
  • Lungs. Looking first at the lung roots, one sees relatively dense shadows caused by the presence of the blood-filled pulmonary and bronchial vessels, the large bronchi, and the lymph nodes (Fig. 3-55). The lung fields, by virtue of the air they contain, readily permit the passage of x-rays. For this reason, the lungs are more translucent on full inspiration than on expiration. The pulmonary blood vessels are seen as a series of shadows radiating from the lung root. When seen end on, they P.134
    appear as small, round, white shadows. The large bronchi, if seen end on, also cast similar round shadows. The smaller bronchi are not seen.
    Figure 3-56 Main features observable in the posteroanterior radiograph of the chest shown in Figure 3-55. Note the position of the patient in relation to the x-ray source and cassette holder.
  • Mediastinum. The shadow is produced by the various structures within the mediastinum, superimposed one on the other (Figs. 3-49 and 3-55). Note the outline of the heart and great vessels. The transverse diameter of the heart should not exceed half the width of the thoracic cage. Remember that on deep inspiration, when the diaphragm descends, the vertical length of the heart increases and the transverse diameter is narrowed. In infants, the heart is always wider and more globular in shape than in adults.

The right border of the mediastinal shadow from above downward consists of the right brachiocephalic vein, the superior vena cava, the right atrium, and sometimes the inferior vena cava (Figs. 3-55 and 3-56). The left border consists of a prominence, the aortic knuckle, caused by the aortic arch; below this are the left margin of the pulmonary trunk, the left auricle, and the left ventricle (Figs. 3-55 and 3-56). The inferior border of the mediastinal shadow (lower border of the heart) blends with the diaphragm and liver. Note the cardiophrenic angles. Right Oblique Radiograph A right oblique radiograph is obtained by rotating the patient so that the right anterior chest wall is touching the cassette holder and the x-rays traverse the thorax from posterior to anterior in an oblique direction (Figs. 3-57 and 3-58). The P.135
heart shadow is largely made up by the right ventricle. A small part of the posterior border is formed by the right atrium. For further details of structures seen on this view, see Figures 3-57 and 3-58.

Figure 3-57 Right oblique radiograph of the chest of a normal adult man after a barium swallow.

Left Oblique Radiograph A left oblique radiograph is obtained by rotation of the patient so that the left anterior chest wall is touching the cassette holder and the x-rays traverse the thorax from posterior to anterior in an oblique direction. The heart shadow is largely made up of the right ventricle anteriorly and the left ventricle posteriorly. Above the heart, the aortic arch and the pulmonary trunk may be seen. An example of a left lateral radiograph of the chest is shown in Figures 3-59 and 3-60. Bronchography and Contrast Visualization of the Esophagus Bronchography is a special study of the bronchial tree by means of the introduction of iodized oil or other contrast medium into a particular bronchus or bronchi, usually under fluoroscopic control. The contrast media are nonirritating and sufficiently radiopaque to allow good visualization of the bronchi (Fig. 3-61). After the radiographic examination is completed, the patient is asked to cough and expectorate the contrast medium. P.136

Figure 3-58 Main features observable in the right oblique radiograph of the chest shown in Figure 3-57. Note the position of the patient in relation to the x-ray source and cassette holder.

Contrast visualization of the esophagus (Figs. 3-57 and 3-59) is accomplished by giving the patient a creamy paste of barium sulfate and water to swallow. The aortic arch and the left bronchus cause a smooth indentation on the anterior border of the barium-filled esophagus. This procedure can also be used to outline the posterior border of the left atrium in a right oblique view. An enlarged left atrium causes a smooth indentation of the anterior border of the barium-filled esophagus. Coronary Angiography The coronary arteries can be visualized by the introduction of radiopaque material into their lumen. Under fluoroscopic control, a long narrow catheter is passed into the ascending aorta via the femoral artery in the leg. The tip of the catheter is carefully guided into the orifice of a coronary artery and a small amount of radiopaque material is injected to reveal the lumen of the artery and its branches. The information can be recorded on radiographs (Fig. 3-62) P.137
or by cineradiography. Using this technique, pathologic narrowing or blockage of a coronary artery can be identified.

Figure 3-59 Left lateral radiograph of the chest of a normal adult man after a barium swallow.

CT Scanning of the Thorax CT scanning relies on the same physics as conventional x-rays but combines it with computer technology. A source of x-rays moves in an arc around the thorax and sends out a beam of x-rays. The beams of x-rays, having passed through the thoracic wall and the thoracic viscera, are converted into electronic impulses that produce readings of the density of the tissue in a 1-cm slice of the body. From these readings, the computer assembles a picture of the thorax called a CT scan, which can be viewed on a fluorescent screen and then photographed (Figs. 3-53 and 3-54). P.138

Figure 3-60 Main features observable in a left lateral radiograph of the chest shown in Figure 3-59. Note the position of the patient in relation to the x-ray source and cassette holder.

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Figure 3-61 Posteroanterior bronchogram of the chest.
Figure 3-62 Coronary angiograms. A. An area of extreme narrowing of the circumflex branch of the left coronary artery (white arrow). B. The same artery after percutaneous transluminal coronary angioplasty. Inflation of the luminal balloon has dramatically improved the area of stenosis (white arrow).

Clinical Problem Solving Study the following case histories and select the best answer to the question following them. A 55-year-old man states that he has noticed an alteration in his voice. He has lost 40 lb (18 kg) and has a persistent cough with blood-stained sputum. He smokes 50 cigarettes a day. On examination, the left vocal fold is immobile and lies in the adducted position. A posteroanterior chest radiograph reveals a large mass in the upper lobe of the left lung with an increase in width of the mediastinal shadow on the left side. 1. The symptoms and signs displayed by this patient can be explained by the following statements except which? (a) This patient has advanced carcinoma of the bronchus in the upper lobe of the left lung, which was seen as a mass on the chest radiograph. (b) The carcinoma has metastasized to the bronchomediastinal lymph nodes, causing their enlargement and producing a widening of the mediastinal shadow seen on the chest radiograph. (c) The enlarged lymph nodes had pressed on the left recurrent laryngeal nerve. (d) Partial injury to the recurrent laryngeal nerve resulted in paralysis of the abductor muscles of the vocal cords, leaving the adductor muscles unopposed. (e) The enlarged lymph nodes pressed on the left recurrent nerve as it ascended to the neck anterior to the arch of the aorta. View Answer1. E. The left recurrent laryngeal nerve ascends to the neck by passing under the arch of the aorta; it ascends in the groove between the trachea and the esophagus. A 35-year-old woman had difficulty in breathing and sleeping at night. She says she falls asleep only to wake up with a choking sensation. She finds that she has to sleep propped up in bed on pillows with her neck flexed to the right. 2. The following statements concerning this case are correct except which? (a) Veins in the skin at the root of the neck are congested. (b) The U-shaped cartilaginous rings in the wall of the trachea prevent it from being kinked or compressed. (c) The left lobe of the thyroid gland is larger than the right lobe. (d) On falling asleep, the patient tends to flex her neck laterally over the enlarged left thyroid lobe. (e) The enlarged thyroid gland extends down the neck into the superior mediastinum. (f) The brachiocephalic veins in the superior mediastinum were partially obstructed by the enlarged thyroid gland. View Answer2. B. The trachea is a mobile, fibroelastic tube that can be kinked or compressed despite the presence of the cartilaginous rings. A 15-year-old boy was rescued from a lake after falling through thin ice. The next day, he developed a severe cold, and 3 days later his general condition deteriorated. He became febrile and started to cough up blood-stained sputum. At first, he had no chest pain, but later, when he coughed, he experienced severe pain over the right fifth intercostal space in the midclavicular line. 3. The following statements would explain the patient’s signs and symptoms except which? (a) The patient had developed lobar pneumonia and pleurisy in the right lung. (b) Disease of the lung does not cause pain until the parietal pleura is involved. (c) The pneumonia was located in the right middle lobe. (d) The visceral pleura is innervated by autonomic nerves that contain pain fibers. (e) Pain associated with the pleurisy was accentuated when movement of the visceral and parietal pleurae occurred, for example, on deep inspiration or coughing. View Answer3. D. Lung tissue and the visceral pleura are not innervated with pain fibers. The costal parietal pleura is innervated by the intercostal nerves, which have pain endings in the pleura. A 2-year-old boy was playing with his toy car when his baby-sitter noticed that a small metal nut was missing from the car. Two days later the child developed a cough and became febrile. 4. This child’s illness could be explained by the following statements except which? (a) The child had inhaled the nut. (b) The metal nut could easily be seen on posteroanterior and right oblique radiographs. (c) The left principal bronchus is the more vertical and wider of the two principal bronchi, and inhaled foreign bodies tend to become lodged in it. (d) The nut was successfully removed through a bronchoscope. (e) Children who are teething tend to suck on hard toys. View Answer4. C. The right principal (main) bronchus is the more vertical and wider of the two principal bronchi and for this reason an inhaled foreign body passes down the trachea and tends to enter the right main bronchus, where it was lodged in this patient. A 23-year-old woman was examined in the emergency department because of the sudden onset of respiratory distress. The physician was listening to breath sounds over the right hemithorax and was concerned when no sounds were heard on the front of the chest at the level of the 10th rib in the midclavicular line. 5. The following comments concerning this patient are correct except which? (a) In a healthy individual, the lower border of the right lung in the midclavicular line in the midrespiratory position is at the level of the sixth rib. (b) The parietal pleura in the midclavicular line crosses the 10th rib. (c) The costodiaphragmatic recess is situated between the lower border of the lung and the parietal pleura. (d) The lung on extreme inspiration could descend in the costodiaphragmatic recess only as far as the eighth rib. (e) No breath sounds were heard because the stethoscope was located over the liver. View Answer5. B. The parietal pleura in the midclavicular line only extends down as far as the eighth rib. A 61-year-old man was seen in the emergency department complaining of a feeling of pressure within his chest. On questioning, he said that he had several attacks before and that they had always occurred when he was climbing stairs or digging in the garden. He found that the discomfort disappeared with rest after about 5 minutes. The reason he came to the emergency department was that the chest discomfort had occurred with much less exertion. 6. The following comments concerning this case are correct except which? (a) The diagnosis is a classic case of angina pectoris. (b) The sudden change in history, that is, pain caused by less exertion, should cause the physician concern that the patient now has unstable angina or an actual myocardial infarction. (c) The afferent pain fibers from the heart ascend to the central nervous system through the cardiac branches of the sympathetic trunk to enter the spinal cord. (d) The afferent pain fibers enter the spinal cord via the posterior roots of the 10th to the 12th thoracic nerves. (e) Pain is referred to dermatomes supplied by the upper four intercostal nerves and the intercostal brachial nerve. View Answer6. D. The afferent pain fibers from the heart enter the spinal cord via the posterior nerve roots of the upper four thoracic spinal nerves. A 55-year-old woman has severe aortic incompetence, with the blood returning to the cavity of the left ventricle during ventricular diastole. 7. To hear the aortic valve with the least interference from the other heart sounds, the best place to place your stethoscope on the chest wall is (a) the right half of the lower end of the body of the sternum. (b) the medial end of the second right intercostal space. (c) the medial end of the second left intercostal space. (d) the apex of the heart. (e) the fifth left intercostal space 3.5 in. (9 cm) from the midline. View Answer7. B A 33-year-old woman was jogging across the park at 11 p.m. when she was attacked by a gang of youths. After she was brutally mugged and raped, one of the youths decided to stab her in the heart to keep her silent. Later in the emergency department she was unconscious and in extremely poor shape. A small wound about 0.5 in. in diameter was present in the left fifth intercostal space about 0.5 in. from the lateral sternal margin. Her carotid pulse was rapid and weak, and her neck veins were distended. No evidence of a left-sided pneumothorax existed. A diagnosis of cardiac tamponade was made. 8. The following observations are in agreement with the diagnosis except which? (a) The tip of the knife had pierced the pericardium. (b) The knife had pierced the anterior wall of the left ventricle. (c) The blood in the pericardial cavity was under right ventricular pressure. (d) The blood in the pericardial cavity pressed on the thin-walled atria and large veins as they traversed the pericardium to enter the heart. (e) The backed-up venous blood caused congestion of the veins seen in the neck. (f) The poor venous return severely compromised the cardiac output. (g) A left-sided pneumothorax did not occur because the knife passed through the cardiac notch. View Answer8. B. The knife had pierced the anterior wall of the right ventricle. A 36-year-old woman with a known history of emphysema (dilatation of alveoli and destruction of alveolar walls with a tendency to form cystic spaces) suddenly experiences a severe pain in the left side of her chest, is breathless, and is obviously in a state of shock. 9. Examination of this patient reveals the following findings except which? (a) The trachea is displaced to the right in the suprasternal notch. (b) The apex beat of the heart can be felt in the fifth left intercostal space just lateral to the sternum. (c) The right lung is collapsed. (d) The air pressure in the left pleural cavity is at atmospheric pressure. (e) The air has entered the left pleural cavity as the result of rupture of one of the emphysematous cysts of the left lung (left-sided pneumothorax). (f) The elastic recoil of the lung tissue caused the lung to collapse. View Answer9. C. The left lung collapsed immediately when air entered the left pleural cavity because the air pressures within the bronchial tree and in the pleural cavity were then equal. A wife was told that her husband was suffering from cancer of the lower end of the esophagus. The physician told her that to save his life, the surgeon would have to remove the lower part of the esophagus, the stomach, the spleen, and the upper part of the duodenum. The wife could not understand why such a drastic operation was required to remove such a small tumor. 10. The following statements explain this extensive operation except which? (a) Carcinoma of the esophagus tends to spread via the lymphatic vessels. (b) The lymphatic vessels descend through the aortic opening in the diaphragm to enter the celiac lymph nodes. (c) The tumor of the esophagus and an area of normal adjacent esophagus have to be removed. (d) The lymphatic vessels and nodes that drain the diseased area have to be removed. (e) Because of the risk that retrograde spread had occurred, the other organs draining into the lymph nodes also have to be removed. View Answer10. B. The lymphatic vessels draining the esophagus accompany the left gastric blood vessels through the esophageal opening in the diaphragm to reach the celiac nodes. A 50-year-old man with chronic alcoholism was told by his physician that he had cirrhosis of the liver with portal hypertension. 11. The following statements explain why the patient recently vomited a cupful of blood except which? (a) The lower third of the esophagus is the site of a portal–systemic anastomosis. (b) At the lower third of the esophagus the esophageal veins of the left gastric vein anastomose with the esophageal veins of the inferior vena cava. (c) In cirrhosis of the liver, the portal circulation through the liver is obstructed by fibrous tissue, producing portal hypertension. (d) Many of the dilated veins that lie within the mucous membrane and submucosa are easily damaged by swallowed food. (e) Copious hemorrhage from these veins is difficult to treat and is often terminal. View Answer11. B. The esophageal veins of the azygos system of veins anastomose with the esophageal veins of the left gastric vein. A 5-year-old boy was seen in the emergency department after an attack of breathlessness during which he had lost consciousness. The mother said that her child had had several attacks before and sometimes his skin had become bluish. Recently, she had noticed that he breathed more easily when he was playing in a squatting position; he also seemed to sleep more easily with his knees drawn up. An extensive workup, including angiography, demonstrated that the patient had severe congenital heart disease. 12. The following observations in this patient are consistent with the diagnosis of tetralogy of Fallot except which? (a) The child was thinner and shorter than normal. (b) His lips, fingers, and toes were cyanotic. (c) A systolic murmur was present down the left border of the sternum. (d) The heart was considerably enlarged to the left. (e) Pulmonary stenosis impairs the pulmonary circulation so that a right to left shunt occurs and the arterial blood is poorly oxygenated. (f) A large ventricular septal defect was present. (g) The aortic opening into the heart was common to both ventricles. View Answer12. D. Because of the pulmonary stenosis and the ventricular septal defect, right ventricular hypertrophy is causing the heart to enlarge to the right. Review Questions Multiple-Choice Questions Select the best answer for each question. 1. The following statements concerning the trachea are true except which? (a) It lies anterior to the esophagus in the superior mediastinum. (b) In deep inspiration, the carina may descend as far as the level of the sixth thoracic vertebra. (c) The left principal bronchus is wider than the right principal bronchus. (d) The arch of the aorta lies on its anterior and left sides in the superior mediastinum. (e) The sensory innervation of the mucous membrane lining the trachea is derived from branches of the vagi and the recurrent laryngeal nerves. View Answer1. C. The right principal bronchus is wider than the left. This is clearly seen in the normal posteroanterior bronchogram shown in Figure 3-54. 2. The following statements concerning the root of the right lung are true except which? (a) The right phrenic nerve passes anterior to the lung root. (b) The azygos vein arches over the superior margin of the lung root. (c) The right pulmonary artery lies posterior to the principal bronchus. (d) The right vagus nerve passes posterior to the lung root. (e) The vessels and nerves forming the lung root are enclosed by a cuff of pleura. View Answer2. C. The right pulmonary artery lies anterior to the principal bronchus. 3. The following statements concerning the right lung are true except which? (a) It possesses a horizontal and an oblique fissure. (b) Its covering of visceral pleura is sensitive to pain and temperature. (c) The lymph from the substance of the lung reaches the hilum by the superficial and deep lymphatic plexuses. (d) The pulmonary ligament permits the vessels and nerves of the lung root to move during the movements of respiration. (e) The bronchial veins drain into the azygos and hemiazygos veins. View Answer3. B. The visceral pleura is innervated by sympathetic and vagal afferent fibers via the pulmonary plexus and is not sensitive to pain and temperature, but it is sensitive to the sensation of stretch. 4. The anterior surface of the heart is formed by the following structures except which? (a) Right ventricle (b) Right atrium (c) Left ventricle (d) Left atrium (e) Right auricle View Answer4. D. The left atrium lies behind the heart. 5. In a posteroanterior radiograph of the thorax, the following structures form the left margin of the heart shadow except which? (a) Left auricle (b) Pulmonary trunk (c) Arch of aorta (d) Left ventricle (e) Superior vena cava View Answer5. E 6. All of the following statements concerning the esophagus are correct except which? (a) It receives an arterial blood supply from both the descending thoracic aorta and the left gastric artery. (b) It is constricted by the presence of the left principal bronchus. (c) It crosses from right to left posterior to the descending aorta. (d) It pierces the diaphragm, with the left vagus on its anterior surface and the right vagus on its posterior surface. (e) It joins the stomach about 16 in. (41 cm) from the incisor teeth. View Answer6. C. The esophagus crosses from right to left anterior to the descending aorta. 7. All of the following statements concerning the mediastinum are correct except which? (a) The mediastinum forms a partition between the two pleural spaces (cavities). (b) The mediastinal pleura demarcates the lateral boundaries of the mediastinum. (c) The heart occupies the middle mediastinum. (d) Should air enter the left pleural cavity, the structures forming the mediastinum are deflected to the right. (e) The anterior boundary of the mediastinum extends to a lower level than the posterior boundary. View Answer7. E. The anterior boundary of the mediastinum extends down to the xiphisternal joint anteriorly—that is, to the level of the ninth thoracic vertebral body. The posterior boundary extends down farther, to the level of the 12th thoracic vertebra. 8. All of the following statements regarding the conducting system of the heart are true except which? (a) The impulse for cardiac contraction spontaneously begins in the sinuatrial node. (b) The atrioventricular bundle is the sole pathway for conduction of the waves of contraction between the atria and the ventricles. (c) The sinuatrial node is frequently supplied by the right and left coronary arteries. (d) The sympathetic nerves to the heart slow the rate of discharge from the sinuatrial node. (e) The atrioventricular bundle descends behind the septal cusp of the tricuspid valve. View Answer8. D. The sympathetic nerves to the heart increase the rate of discharge from the sinuatrial node. 9. All of the following statements regarding the mechanics of inspiration are true except which? (a) The diaphragm is the most important muscle of inspiration. (b) The suprapleural membrane can be raised. (c) The sternum moves anteriorly. (d) The ribs are raised superiorly. (e) The tone of the muscles of the anterior abdominal wall is diminished. View Answer9. B. The suprapleural membrane is composed of fibrous tissue and is attached to the transverse process of the seventh cervical vertebra; it cannot be raised during inspiration. 10. The following statements concerning the lungs are correct except which? (a) Inhaled foreign bodies most frequently enter the right lung. (b) The left lung is in direct contact with the arch of the aorta and the descending thoracic aorta. (c) There are no lymph nodes within the lungs. (d) The structure of the lungs receives its blood supply from the bronchial arteries. (e) The costodiaphragmatic recesses are lined with parietal pleura. View Answer10. C 11. The following statements concerning the blood supply to the heart are correct except which? (a) The coronary arteries are branches of the ascending aorta. (b) The right coronary artery supplies both the right atrium and the right ventricle. (c) The circumflex branch of the left coronary artery descends in the anterior interventricular groove and passes around the apex of the heart. (d) Arrhythmias (abnormal heart beats) can occur after occlusion of a coronary artery. (e) Coronary arteries can be classified as functional end arteries. View Answer11. C. The circumflex branch of the left coronary artery winds around the left margin of the heart in the atrioventricular groove. 12. The following statements concerning the bronchopulmonary segments are correct except which? (a) The veins are intersegmental. (b) The segments are separated by connective tissue septa. (c) The arteries are intrasegmental. (d) Each segment is supplied by a secondary bronchus. (e) Each pyramid-shaped segment has its base pointing toward the lung surface. View Answer12. D. Each segment of the lung is supplied by a segmental bronchus. Completion Questions Match each structure listed below with the region in which it is found. Each lettered answer may be used more than once. 13. Coronary sinus (opening) 14. Moderator band 15. Anulus ovalis 16. Right pulmonary veins (openings) (a) Left atrium (b) Right ventricle (c) Right atrium (d) Left ventricle (e) Right auricle View Answer13. C 14. B 15. C 16. A Multiple-Choice Questions Read the case histories and select the best answer to the question following them. On performing a routine examination of a 7-year-old girl, a pediatrician heard a continuous machinery-like murmur in the second left intercostal space. The murmur occupied both systole and diastole. The child was not cyanotic, the heart was of normal size, and there was no clubbing of the fingers. Radiographic examination of the chest revealed slight enlargement of the left atrium, left ventricle, and pulmonary trunk. A diagnosis of patent ductus arteriosus was made. 17. Based on the clinical history and the diagnosis, the following statements concerning the case are correct except which? (a) The patent ductus represents the distal portion of the sixth left aortic arch artery. (b) The ductus connects the right pulmonary artery to the descending thoracic aorta. (c) The ductus in fetal life is the normal bypass of blood to the aorta from the pulmonary trunk. (d) At birth, the ductus arteriosus normally constricts in response to a rise in arterial oxygen. (e) The ductus arteriosus closes to become the ligamentum arteriosum. View Answer17. B. The ductus arteriosus represents the distal portion of the sixth left aortic arch artery and connects the left pulmonary artery at its origin from the pulmonary trunk to the junction of the aortic arch and the descending thoracic aorta. 18. The presence of a patent ductus presents the following physiologic and pathologic consequences except which? (a) Aortic blood passes into the pulmonary artery, producing the machinery-like murmur. (b) The shunting of blood occurs only during systole as the result of the higher blood pressure in the aorta and the lower blood pressure in the pulmonary artery. (c) The left ventricle shows hypertrophy because of the leak from the aorta. (d) The pulmonary trunk becomes enlarged and the right ventricle hypertrophied owing to the raised pressure in the pulmonary circulation. (e) Because of the risk of bacterial infection of the wall of the pulmonary artery (bacterial endarteritis) caused by the pulmonary hypertension, the patent ductus should be ligated and divided surgically. View Answer18. B. The machinery-like murmur occurs during both systole and diastole and is caused by the shunting of blood from the aorta to the pulmonary artery owing to the higher blood pressure in the aorta during both phases of the cardiac cycle. A 12-year-old boy was examined by a pediatrician and found to have absent femoral pulses in both femoral arteries. The blood pressure in both upper limbs was higher than in both lower limbs. The diagnosis was coarctation of the aorta. 19. The following statements about this case are correct except which? (a) The aorta is narrowed just proximal to the site of origin of the left common carotid artery. (b) There is no femoral pulse because the small aortic pulse wave does not reach the femoral arteries. (c) The high blood pressure in the arteries of the upper limbs and the cerebral circulation is an attempt by the heart to force blood through the narrowed aorta. (d) To compensate for the diminished blood flow into the lower limbs, the internal thoracic, subclavian, and posterior intercostal arteries become dilated. (e) The raised blood pressure proximal to the aortic narrowing may later result in cerebral hemorrhage and heart failure. View Answer19. A P.140
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Footnote *The occurrence of specialized internodal pathways has been dismissed by some researchers, who claim that it is the packaging and arrangement of ordinary atrial myocardial fibers that are responsible for the more rapid conduction.

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