8941d_c21.qxd 8/13/03 2:19 PM Page 249 mac 106 mac 106:Desktop Folder:211_sks: EXERCISE STRUCTURE OF THE HEART 2121 OBJECTIVES MATERIALS After completing this exercise, you should • human heart model be able to: • human torso or chart showing the pulmonary and • Describe the location and coverings of the heart systemic circulations and the three layers of the heart wall • colored pencils • Identify major features of cardiac muscle tissue on • preserved sheep heart (or other mammal heart) a prepared microscope slide • dissecting instruments, trays, disposable gloves, • Identify the major heart structures on models or 5-inch blade knife charts • compound microscope with cardiac muscle slide • Describe the flow of a drop of blood through the (for demonstration) pulmonary and systemic circulations, listing the vessels, chambers, and valves • Describe the changes that take place in the heart after birth • Identify the selected heart structures on a dissected sheep heart our heart beats without external stimulation and rests A. COVERINGS only between heart beats. The heart is a small double Ypump that simultaneously pumps blood to and from AND LAYERS body cells through the systemic circulation and to and from OF THE HEART the lungs through the pulmonary circulation. The heart is about the size of a fist and lies in the thoracic cavity. The base of the heart is the wide superior portion of the heart from which the great vessels emerge, and the apex of the heart is the inferior end pointing to the left. The heart is tilted at an angle so that its inferior surface lies against the diaphragm with two-thirds of the heart to the left side of the sternum. 249 8941d_c21.qxd 7/29/03 3:23 PM Page 250 yesmac1 ymac1:310_CM: 250 EXERCISE 21 STRUCTURE OF THE HEART The heart is located between the lungs in the thoracic ACTIVITY 1COVERINGS AND cavity and is surrounded and protected by the pericardium (peri- ϭ around). The pericardium consists of an outer, LAYERS OF tough fibrous pericardium and an inner, delicate serous THE HEART pericardium. The fibrous pericardium attaches to the di- aphragm and also to the great vessels of the heart. Like all 1 Label the structures on Figure 21.1(a) and (b). serous membranes, the serous pericardium is a double 2 Pronounce each term as you write in the answer. membrane composed of an outer parietal layer and an in- ner visceral layer. Between these two layers is the peri- 3 Using contrasting colors, color the layers of the heart cardial cavity filled with serous fluid. and the pericardium. The wall of the heart has three layers: the outer 4 ϭ ϭ Examine a slide of cardiac muscle tissue. Observe the epicardium (epi- on, upon; cardia heart), the middle striations, branching cardiac cells, nuclei, and interca- myocardium (myo- ϭ muscle), and the inner endocardium ϭ lated discs. Refer to the photomicrograph of cardiac (endo- within, inward). The epicardium is the visceral muscle tissue in Exercise 6 Tissues. layer of the pericardium. The majority of the heart is myo- cardium or cardiac muscle tissue. The endocardium is a thin layer of endothelium deep to the myocardium that lines the chambers of the heart and the valves. 8941d_c21.qxd 8/26/03 1:30 PM Page 251 mac34 Mac34: kec_420: STRUCTURE OF THE HEART 251 1 2 4 3 5 6 7 (a) Heart, anterior view • apex of heart 1 _____________________ • base of heart • diaphragm 2 _____________________ • fibrous pericardium (peri- 3 _____________________ CAR-dee-um) • left lung 4 _____________________ • right lung 5 _____________________ • serous pericardium 6 _____________________ PERICARDIUM Heart wall 7 _____________________ 8 12 9 Trabeculae carneae Coronary blood • endocardium 8 _____________________ vessels • fibrous pericardium 10 9 _____________________ (space) • myocardium 13 • parietal layer of serous 10 ____________________ 11 pericardium • pericardial cavity 11 ____________________ • visceral layer of serous 12 ____________________ pericardium (epicardium) 13 ____________________ (b) Pericardium and layers of heart wall FIGURE 21.1 Layers of the heart and pericardium. 8941d_c21.qxd 7/29/03 3:23 PM Page 252 yesmac1 ymac1:310_CM: 252 EXERCISE 21 STRUCTURE OF THE HEART B. MAJOR return oxygen-poor blood to the right atrium. The superior vena cava returns blood from the head, neck, and arms; HEART STRUCTURES the inferior vena cava returns blood from the body infe- rior to the heart. The coronary sinus is a smaller vein that 1. Surface Structures of the Heart returns blood from the coronary circulation. Blood leaves the right atrium to enter the right ventricle. From here, The human heart has four chambers and is divided into oxygen-poor blood passes out the pulmonary trunk, the right and left sides. Each side has an upper chamber called only vessel that removes blood from the right ventricle. an atrium and a lower chamber called a ventricle. The This large artery divides into the right and left pulmonary two atria form the base of the heart and the tip of the left arteries that carry blood to the lungs where it is oxy- ventricle forms the apex. Auricles (auricle ϭ little ear) are genated. Oxygen-rich blood returns to the left atrium pouch-like extensions of the atria with wrinkled edges. through two right and two left pulmonary veins. The Shallow grooves called sulci (sulcus, singular) externally blood then passes into the left ventricle that pumps blood mark the boundaries between the four heart chambers. into the large aorta. The aorta distributes blood to the sys- Although a considerable amount of external adipose tissue temic circulation. The aorta begins as a short ascending is present on the heart surface for cushioning, most heart aorta, curves to the left to form the aortic arch, descends models do not show this. posteriorly and continues as the descending aorta. Cardiac muscle tissue that composes the heart walls has In fetal life, oxygen is obtained through the placenta its own blood supply and circulation, the coronary (cor- from the mother and not from the lungs. Therefore, it is ona ϭ crown) circulation. Coronary blood vessels en- not detrimental to the baby’s health for blood to bypass the compass the heart similar to a crown and are found in sulci. lungs. The fetal heart contains a short, temporary vessel, On the anterior surface of the heart, the right and left the ductus arteriosus (ductus ϭ duct; arteria ϭ artery), coronary arteries branch off the base of the ascending that connects the pulmonary trunk and the aorta. The duc- aorta just superior to the aortic semilunar valve, and travel tus arteriosus is a right heart to left heart shunt that reroutes in the sulcus separating the atria and ventricles. These small some of the blood destined for the lungs to the systemic arteries are supplied with blood when the ventricles are circulation through the aorta. The ductus arteriosus resting. When the ventricles contract, the cusps of the aor- changes into a ligament after birth and remains as the liga- tic valve open to cover the openings to the coronary arter- mentum arteriosum. ies. A clinically important branch of the left coronary ar- tery is the anterior interventricular branch, also known as the left anterior descending (LAD) branch that lies ACTIVITY 2 EXTERNAL STRUCTURES between the right and left ventricles and supplies both ven- OF THE HEART tricles with oxygen-rich blood. This coronary artery is commonly occluded which can result in a myocardial in- 1 Label the structures on Figure 21.2(a) and (b). farct and, at times, death. 2 Using contrasting colors, color the heart structures in Figure 21.2(a) and (b). 2. Great Vessels of the Heart 3 Identify each term on models or charts. 4 Pronounce each term as you point to it. The great veins of the heart return blood to the atria and the great arteries carry blood away from the ventricles. The superior vena cava, inferior vena cava, and coronary sinus 8941d_c21.qxd 7/29/03 11:32 AM Page 253 yesmac1 ymac1:310_CM: STRUCTURE OF THE HEART 253 • aortic arch • left ventricle 1 ________________________________ • ascending aorta • ligamentum arteriosum • auricle of left atrium • pulmonary trunk 2 ________________________________ • auricle of right atrium • right coronary artery 3 ________________________________ • branch of left coronary artery or LAD • right pulmonary artery • descending aorta • right pulmonary veins 4 ________________________________ • inferior vena cava • right ventricle 5 ________________________________ • left pulmonary artery • superior vena cava • left pulmonary veins 6 ________________________________ 7 ________________________________ 1 10 8 ________________________________ 11 2 9 ________________________________ 12 3 10 ______________________________ 13 4 11 _______________________________ 14 5 12 ______________________________ 13 _______________________________ 6 15 7 14 ______________________________ 15 _______________________________ 8 16 16 ______________________________ 17 _______________________________ 9 17 (a) Anterior view showing surface features • aortic arch • left pulmonary veins • ascending aorta • ligamentum arteriosum • coronary sinus • right pulmonary artery 18 23 • inferior vena cava • right pulmonary veins 19 24 • left pulmonary artery • superior vena cava 20 25 18 ______________________________ 21 19 _______________________________ 26 20 ______________________________ 21 _______________________________ 22 22 ______________________________ 23 _______________________________ 24 ______________________________ 25 _______________________________ 27 26 _______________________________