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Saladin 6E Outline Chapter 19 The SALADIN 6E OUTLINE CHAPTER 19 THE CIRCULATORY SYSTEM: THE HEART I. Overview of the Cardiovascular System (pp. 715–716) A. The cardiovascular system consists of the heart and the blood vessels. (p. 715) (Fig. 19.1) 1. The broader term circulatory system also includes the blood. 2. Some authorities use the term circulatory system to include the lymphatic system. B. The cardiovascular system has two major divisions: a pulmonary circuit and a systemic circuit. (pp. 715–716) 1. The right side of the heart furnishes blood to the pulmonary circuit, which carries blood to the lungs and returns it to the heart. a. It receives blood that has circulated through the body and has high CO2 and wastes. b. It pumps the blood into the pulmonary trunk, which divides into the right and left pulmonary arteries. c. These transport blood to the air sacs (alveoli) of the lungs where CO2 is unloaded and O2 is picked up. d. The O2-rich blood then flows by way of the pulmonary veins to the left side of the heart. 2. The left side supplies the systemic circuit, which carries blood to the body’s tissues and returns it to the heart. a. It receives blood from the pulmonary veins. b. It pumps the blood into the aorta. The aorta makes a U-turn at the aortic arch, which supplies the head, neck, and upper limbs, and passes downward. c. The aorta travels through the thoracic and abdominal cavities and issues smaller arteries to organs before branching into the lower limbs. d. After circulating, the deoxygenated systemic blood returns to the right side of the heart via the superior vena cava and the inferior vena cava. C. The heart is located in the thoracic cavity in the mediastinum, between the lungs and deep to the sternum. (p. 716) 1. It is tilted toward the left from superior to inferior midpoints, so about two-thirds of the heart lies to the left of the median plane. (Figs. 19.2, B.10–B.11, p. 390) 2. The broad superior portion is called the base and is the point of attachment for the great vessels. 3. The inferior end tapers to a blunt point, the apex, just above the diaphragm. Saladin Outline Ch.19 Page 2 4. The adult heart is about 9 cm (3.5 in.) wide at the base, 13 cm (5 in.) from base to apex, and 6 cm (2.5 in.) from anterior to posterior—about the size of one’s fist; it weighs about 300 g (10 oz.). D. The pericardium is a double-walled sac that encloses the heart. (p. 716) (Fig. 19.3) 1. The outer wall is the pericardial sac (parietal pericardium) that has a tough, fibrous layer of dense irregular connective tissue and a deep, thin serous layer. 2. The serous layer turns inward at the base of the heart to form the epicardium (visceral pericardium) covering the heart surface. 3. The pericardial sac is anchored by ligaments to the diaphragm and sternum, and by fibrous connective tissue to the mediastinal tissue. 4. Between the parietal and visceral membranes is a space called the pericardial cavity. (Figs. 19.2b, 19.3) a. This cavity contains 5 to 30 mL of pericardial fluid, exuded by the serous pericardium; this fluid lubricates the membranes and reduces friction when the heart beats. b. In pericarditis, inflammation of the pericardium, the membranes may produce a painful friction rub with each heartbeat. 5. The pericardium isolates the heart from other thoracic organs and allows it room to expand, while resisting excessive expansion. II. Gross Anatomy of the Heart (pp. 717–725) A. The heart wall consists of three layers: epicardium, myocardium, and endocardium. (pp. 717–718) 1. The epicardium (visceral pericardium) is a serous membrane on the heart surface. a. It is mainly simple squamous epithelium overlying a thin layer of areolar tissues. b. In some places it has a thick layer of adipose tissue but in other areas is fat free and translucent. (Figs. 19.4a, 19.5) c. The largest branches of coronary blood vessels travel through the epicardium. 2. The endocardium is similar and lines the interior of the heart chambers. (Figs. 19.3, 19.4b) a. It has similar structure but has no adipose tissue. b. Endocardium covers the valve surfaces and is continuous with the endothelium of blood vessels. 3. The myocardium between the other two layers is composed of cardiac muscle and is the thickest layer; it performs the work of the heart. a. Its thickness varies from one heart chamber to another and is proportional to the workload. Saladin Outline Ch.19 Page 3 b. Its muscle spirals around the heart forming myocardial vortex, so upon contraction a twisting or wringing motion occurs. (Fig. 19.6) 4. The heart also has a framework of collagenous and elastic fibers that make up the fibrous skeleton. a. This tissue is especially concentrated in the walls between the heart chambers, in fibrous rings (anuli fibrosi) around the valves, and in sheets of tissue that interconnect these rings. (Fig. 19.8) b. The fibrous skeleton has multiple functions. i. It provides structural support, especially around the valves and openings of the great vessels. ii. It anchors the cardiac muscle cells (cardiocytes) and provides leverage. iii. It serves as electrical insulation between atria and ventricles. iv. Its elastic recoil may aid in refilling the heart with blood after each beat. B. The heart has four chambers best seen in frontal section. (pp. 718–719) (Figs. 19.4b, 19.7) 1. The two chambers at the superior pole (base) are the right and left atria. a. They are thin walled and receive blood returning to the heart by way of the great veins. b. Most of the mass is on the posterior side of the heart, and in the anterior view, each has a small earlike extension called an auricle that slightly increases the volume. (Fig. 19.5a) 2. The inferior chambers, the right and left ventricles, are pumps that eject blood into the arteries. a. The right ventricle constitutes most of the anterior aspect of the heart. b. The left ventricle forms the apex and inferoposterior aspect. 3. On the surface three sulci (grooves) mark the boundaries of the four chambers; these sulci are largely filled by fat and the largest of the coronary blood vessels. (Fig. 19.5a) a. The coronary (atrioventricular) sulcus encircles the heart near the base and separates the atria from the ventricles below. b. The other two sulci extend obliquely down the heart from the coronary sulcus toward the apex. i. The one on the front is the anterior interventricular sulcus. ii. The one on the back is the posterior interventricular sulcus. c. These two sulci overlie an internal wall, the interventricular septum, that divides the right ventricle from the left. Saladin Outline Ch.19 Page 4 4. The atria have thin flaccid walls corresponding to their relatively light workload of pumping blood into the ventricles below. (Fig. 19.7) a. They are separated by a wall called the interatrial septum. b. The right atrium and both auricles exhibit internal ridges of myocardium called pectinate muscles. 5. The ventricles are separated by the interventricular septum, a much more muscular, vertical wall. a. The right ventricle pumps blood to the lungs, and is only moderately muscular. b. The left ventricle wall is two to four times as thick, since it pumps blood through the entire body. c. Both ventricles exhibit internal ridges called trabeculae carneae. C. The valves of the heart ensure a one-way blood flow. (pp. 719–722) (Fig. 19.7) 1. A valve lies between each atrium and its ventricle and at the exit of each ventricle into its great artery, but no valve lies where the great veins empty into the atria. 2. Each valve consists of two or three flaps called cusps or leaflets, covered with endocardium. 3. The atrioventricular (AV) valves regulate the openings between the atria and ventricles. a. The right AV (tricuspid) valve has three cusps, and the left AV (bicuspid) has two. (Fig. 19.8) b. The left AV is also known as the mitral valve. c. Stringlike tendinous cords (chordae tendineae) connect the valve cusps to conical papillary muscles on the floor of the ventricle and prevent the AV valves from flipping inside out. 4. The semilunar valves (pulmonary and aortic valves) regulate the flow of blood from the ventricles into the great arteries. a. The pulmonary valve controls the opening from the right ventricle into the pulmonary trunk. b. The aortic valve controls the opening from the left ventricle into the aorta. c. Each valve has three cusps; there are no tendinous cords. 5. The valves make no muscular effort but are simply pushed open and closed by the blood pressure as the chambers contract and relax. D. Blood flow is kept entirely separate on the right and left sides of the heart. (pp. 722–723) (Fig. 19.9) E. The blood vessels of the heart wall constitute the coronary circulation. (pp. 723–725) Saladin Outline Ch.19 Page 5 1. At rest, the coronary blood vessels supply the myocardium with about 250 mL of blood per minute, or about 5% of the circulating blood, even though the heart is only 0.5% of the body’s weight. 2. The coronary circulation is the most variable aspect of cardiac anatomy, and its description is the pattern seen in 70% to 85% of people. 3. The arterial supply begins immediately after the aorta leaves the left ventricle.
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