11 The Cardiovascular System WHAT The cardiovascular system delivers oxygen and HOW nutrients to the body tissues The heart pumps and carries away wastes blood throughout the body such as carbon dioxide in blood vessels. Blood flow via blood. requires both the pumping action of the heart and changes in blood pressure. WHY If the cardiovascular system cannot perform its functions, wastes build up in tissues. INSTRUCTORS Body organs fail to function properly, New Building Vocabulary and then, once oxygen becomes Coaching Activities for this depleted, they will die. chapter are assignable in hen most people hear the term cardio- only with the interstitial fluid in their immediate Wvascular system, they immediately think vicinity. Thus, some means of changing and of the heart. We have all felt our own “refreshing” these fluids is necessary to renew the heart “pound” from time to time when we are ner- nutrients and prevent pollution caused by vous. The crucial importance of the heart has been the buildup of wastes. Like a bustling factory, the recognized for ages. However, the cardiovascular body must have a transportation system to carry system is much more than just the heart, and its various “cargoes” back and forth. Instead of from a scientific and medical standpoint, it is roads, railway tracks, and subways, the body’s important to understand why this system is so vital delivery routes are its hollow blood vessels. to life. Most simply stated, the major function of the Night and day, minute after minute, our tril- cardiovascular system is transportation. Using lions of cells take up nutrients and excrete wastes. blood as the transport vehicle, the system carries Although the pace of these exchanges slows dur- oxygen, nutrients, cell wastes, hormones, and ing sleep, they must go on continuously: when many other substances vital for body homeostasis they stop, we die. Cells can make such exchanges to and from the cells. The force to move the blood 356 Chapter 11: The Cardiovascular System 357 Superior Aorta vena cava Parietal pleura (cut) Pulmonary Left lung trunk Pericardium (cut) Apex of heart Diaphragm (a) Figure 11.1 Location of the heart within the thorax. (a) Relationship of the JGCTV|CPFITGCVXGUUGNUVQVJGNWPIU (Figure continues on page 358.) around the body is provided by the beating heart flanked on each side by the lungs (Figure 11.1). Its and by blood pressure. pointed apex is directed toward the left hip and The cardiovascular system includes a muscular rests on the diaphragm, approximately at the level pump equipped with one-way valves and a system of the fifth intercostal space. (This is exactly where of large and small “plumbing” tubes within which one would place a stethoscope to count the heart the blood travels. (We discussed blood, the sub- rate for an apical pulse.) Its broad posterosuperior stance transported, in Chapter 10.) Here we will aspect, or base, from which the great vessels of the consider the heart (the pump) and the blood ves- body emerge, points toward the right shoulder and sels (the “plumbing”). lies beneath the second rib. 11 Coverings and Walls of the Heart The Heart The heart is enclosed by a sac called the pericar- Anatomy of the Heart dium (per″i-kar′de-um) that is made up of three layers: an outer fibrous layer and an inner serous ➔ Learning Objective membrane pair. The loosely fitting superficial part □ Describe the location of the heart in the body, of this sac is referred to as the fibrous pericar- CPF|KFGPVKH[KVUOCLQTCPCVQOKECNCTGCUQPCP dium. This fibrous layer helps protect the heart appropriate model or diagram. and anchors it to surrounding structures, such as Size, Location, and Orientation the diaphragm and sternum. Deep to the fibrous pericardium is the slippery, two-layered serous The modest size and weight of the heart give few pericardium. The parietal layer of the serous peri- hints of its incredible strength. Approximately the cardium, or parietal pericardium, lines the inte- size of a person’s fist, the hollow, cone-shaped heart rior of the fibrous pericardium. At the superior weighs less than a pound. Snugly enclosed within aspect of the heart, this parietal layer attaches to the inferior mediastinum (me″de-as-ti′num), the the large arteries leaving the heart and then makes medial section of the thoracic cavity, the heart is 358 Essentials of Human Anatomy and Physiology Mediastinum Midsternal line 2nd rib Heart Sternum Right lung Diaphragm Point of maximal intensity (PMI) Posterior (b) (c) Figure 11.1 (continued) Location of the heart within the thorax. (b)|4GNCVKQPUJKRQHVJGJGCTVVQVJGUVGTPWOCPFTKDU (c) Cross-sectional XKGY|UJQYKPITGNCVKXGRQUKVKQPQHVJGJGCTVKPVJGVJQTCZ a U-turn and continues inferiorly over the heart myocardium is reinforced internally by a network of surface. The visceral layer of the serous pericar- dense fibrous connective tissue called the “skeleton dium, or visceral pericardium, also called the of the heart.” The endocardium (en″do-kar′de-um) epicardium, is part of the heart wall (Figure 11.2). is a thin, glistening sheet of endothelium that lines In other words, the epicardium is the innermost the heart chambers. It is continuous with the linings layer of the pericardium and the outermost layer of of the blood vessels leaving and entering the heart. the heart wall. Lubricating serous fluid is produced (Figure 11.3 shows two views of the heart—an exter- by the serous pericardial membranes and collects nal anterior view and a frontal section. As the ana- in the pericardial cavity between these serous lay- tomical areas of the heart are described in the next ers. This fluid allows the heart to beat easily in a section, keep referring to Figure 11.3 to locate each relatively frictionless environment as the serous of the heart structures or regions.) pericardial layers slide smoothly across each other. Chambers and Associated Great Homeostatic Imbalance 11.1 Vessels ➔ Learning Objectives Inflammation of the pericardium, pericarditis □ ″ ′ Trace the pathway of blood through the heart. (per ˘ı-kar-di tis), often results in a decrease in the □ already small amount of serous fluid. This causes Compare the pulmonary and systemic circuits. the pericardial layers to rub, bind, and stick to The heart has four hollow cavities, or chambers— each other, forming painful adhesions that inter- two atria (a′tre-ah; singular atrium) and two ven- fere with heart movements. ___________________✚ tricles (ven′tr˘ı-kulz). Each of these chambers is The heart walls are composed of three layers: the lined with endocardium, which helps blood flow outer epicardium (the visceral pericardium just smoothly through the heart. The superior atria are described), the myocardium, and the innermost primarily receiving chambers. As a rule, they are endocardium (see Figure 11.2). The myocardium not important in the pumping activity of the heart. (mi″o-kar′de-um) consists of thick bundles of cardiac Instead, they assist with filling the ventricles. Blood muscle twisted and whorled into ringlike arrange- flows into the atria under low pressure from the ments (see Figure 6.2b, p. 184). It is the layer that veins of the body and then continues on to fill actually contracts. Myocardial cells are linked together the ventricles. The inferior, thick-walled ventricles by intercalated discs, which contain both desmo- are the discharging chambers, or actual pumps of somes and gap junctions. The gap junctions at the the heart. When they contract, blood is propelled intercalated discs allow ions to flow from cell to cell, out of the heart and into circulation. The right ven- carrying a wave of excitement across the heart. The tricle forms most of the heart’s anterior surface; the left ventricle forms its apex (Figure 11.3a). The Chapter 11: The Cardiovascular System 359 Pulmonary Fibrous trunk pericardium Parietal layer of serous pericardium Pericardium Pericardial cavity Visceral layer of serous pericardium Epicardium Myocardium Heart wall Endocardium Heart chamber Figure 11.2 Heart wall and coverings.0QVGVJCVVJGXKUEGTCNNC[GTQHVJG RGTKECTFKWOCPFVJGGRKECTFKWOQHVJGJGCTVYCNNCTGVJGUCOGUVTWEVWTG Brachiocephalic trunk Left common carotid artery Superior vena cava Left subclavian artery Right pulmonary artery Aortic arch Ligamentum arteriosum Ascending aorta Left pulmonary artery Pulmonary trunk Left pulmonary veins Right pulmonary Left atrium veins Right atrium Circumflex artery Right coronary artery 11 in coronary sulcus (right Left coronary artery in atrioventricular groove) coronary sulcus (left atrioventricular groove) Anterior cardiac vein Left ventricle Right ventricle Great cardiac vein Marginal artery Anterior interventricular Small cardiac vein artery (in anterior interventricular sulcus) Inferior vena cava Apex (a) Anterior view of heart showing major vessels Figure 11.3 Gross anatomy of the heart. (Figure continues on page 360.) 360 Essentials of Human Anatomy and Physiology Superior vena cava Aorta Left pulmonary artery Right pulmonary artery Left atrium Right atrium Left pulmonary veins Right pulmonary veins Pulmonary semilunar valve Left atrioventricular valve Fossa ovalis (bicuspid valve) Aortic semilunar valve Right atrioventricular valve (tricuspid valve) Left ventricle Right ventricle Chordae tendineae Interventricular septum Inferior vena cava Myocardium Visceral pericardium (epicardium) (b) Frontal section showing interior chambers and valves Figure 11.3 (continued) Gross anatomy of the heart. septum that divides the heart longitudinally is (oxygen enters the blood and carbon dioxide enters referred to as the interatrial septum where it the lungs) and then return it to the heart. divides the atria and the interventricular septum Oxygen-rich blood returned to the left atrium where it divides the ventricles. flows into the left ventricle and is pumped out into Although it is a single organ, the heart functions the aorta (a-or′tah), from which the systemic arter- as a double pump, with arteries carrying blood away ies branch to supply essentially all body tissues. from and veins carrying blood toward the heart. The After oxygen is delivered to tissues, oxygen-poor right side works as the pulmonary circuit pump.