Name: Date: Period:

Anatomy of the

Objectives: 1. To describe the location of the heart.

2. To name and locate the major anatomical areas and structures of the heart when provided with an appropriate model or diagram, or with a dissected sheep heart, and to explain the function of each.

3. To trace the pathway of blood through the heart.

4. To explain why the heart is called a double pump, and to compare the pulmonary and systemic circuits.

5. To explain the operation of the atrioventricular and semilunar valves.

6. To name and describe the functional blood supply of the heart.

INTRODUCTION The major function of the cardiovascular system is transportation. Using blood as the transport vehicle, the system carries oxygen, digested foods, cell wastes, electrolytes, and many other substances vital to the body's homeostasis to and from the body cells. The system's propulsive force is the contracting heart, which can be compared to a muscular pump equipped with one-way valves. As the heart contracts, it forces blood into a closed system of large and small plumbing tubes (blood vessels) within which the blood is confined and circulated. This exercise deals with the structure of the heart, or circulatory pump.

Questions: 1. What is the major function of the cardiovascular system? ______2. What is the system’s propulsive force? ______

GROSS ANATOMY OF THE HUMAN HEART The heart is a cone-shaped organ, approximately the size of a fist, and is located within the mediastinum, or medial cavity, of the thorax. It is flanked laterally by the lungs, posteriorly by the vertebral column, and anteriorly by the sternum. Its more pointed apex extends slightly to the left and rests on the diaphragm, approximately at the level of the fifth intercostal space. Its broader base, from which the great vessels emerge, lies beneath the second rib and points toward the right shoulder. The right of the heart forms most of its anterior surface. Figure A & B shows two views of the heart-an external anterior view and a frontal section. As its anatomical regions are described in the text, consult the figure. The heart is enclosed within a double-walled sac called the . The thin visceral pericardium, or epicardium, which is closely applied to the heart muscle, reflects downward at the base of the heart to form its companion serous membrane, the loosely applied parietal pericardium, which is attached at the heart apex to the diaphragm. Serous fluid produced by the membranes allows the heart to beat in a relatively frictionless environment. The serous parietal pericardium, in turn, lines the loosely fitting superficial fibrous pericardium composed of dense . Inflammation of the pericardium, pericarditis, causes painful adhesions between the serous pericardial layers. These adhesions interfere with heart movements.

Questions: 3. What is the significance of the apex? ______

4. What is pericarditis? ______

1 - a Anatomy of the human heart. (A) External anterior view; (B) frontal section

2 The walls of the heart are composed mainly of -the myocardium-which is reinforced internally by a dense, fibrous connective tissue network. This network-the fibrous skeleton of the heart-is more elaborate and thicker in certain areas-for example, around the valves and at the bases of the great vessels leaving the heart. The heart is divided into four chambers: two superior atria and two inferior ventricles, each lined with a thin serous lining called the . The septum that divides the heart longitudinally is referred to as the interatrial or , depending on which chambers it partitions. Functionally, the atria are receiving chambers and are relatively ineffective as pumps. Blood flows into the atria, under relatively low pressure, from the veins of the body. The right receives relatively oxygen-poor blood from the body via the superior and inferior . Four pulmonary veins deliver oxygen-rich blood from the lungs to the left atrium. The inferior thick-walled ventricles, which form the bulk of the heart, are the discharging chambers that force blood out of the heart and into the large arteries that emerge from its base. The right ventricle pumps blood into the pulmonary trunk, which routes the blood to the lungs to be oxygenated. The left ventricle discharges blood into the , from which all systemic arteries of the body diverge to supply the body tissues.

Questions: 5. What divides the heart longitudinally (left and right)? ______6. Which chamber (atrium or ventricle) has low pressure and is not described as a pumping chamber? ______7. Pulmonary veins: how many are there? _____ they carry blood from ______to ______, blood in the veins is oxygen rich/oxygen poor? (circle one)

PULMONARY AND SYSTEMIC CIRCULATIONS The heart functions as a double pump. The right side serves as the pump, shunting the carbon dioxide-rich blood entering its chambers to the lungs to unload carbon dioxide and pick up oxygen, and then back to the left side of the heart. The function of this circuit is strictly to provide for gas exchange. The second circuit, which pumps oxygen-rich blood from the left heart through the body tissues and back to the right heart, is called the systemic circulation. It supplies the functional blood supply to all body tissues.

Questions: 8. In your own words, what is the difference between the pulmonary and systemic systems? ______

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HEART VALVES Four valves enforce a one-way blood flow through the heart chambers. The atrioventricular valves, located between the atrial and ventricular chambers on each side, prevent backflow into the atria when the ventricles begin to contract. The left atrioventricular valve, also called the mitral or bicuspid valve, consists of two cusps, or flaps, of endocardium. The right atrioventricular valve, the , has three cusps. Tiny white collagenic cords called the chordae tendineae (literally, heart strings) anchor the cusps to the ventricular walls. The chordae tendineae originate from small bundles of cardiac muscle, papillary muscles, that project from the myocardial wall. When blood is flowing passively into the atria and then into the ventricles during diastole (the period of ventricular relaxation), the atrioventricular valve flaps hang limply into the ventricular chambers and then are carried passively toward the atria by the accumulating blood. When the ventricles begin to contract () and blood in their chambers is compressed, the intraventricular begins to rise, causing the valve flaps to be reflected superiorly and close the valve. The chordae tendineae, pulled taut by the contracting papillary muscles, anchor the flaps in a closed position, preventing backflow into the atria during ventricular contraction. If unanchored, the flaps would blow upward into the atria, rather like an umbrella being turned inside out by a strong wind. 3 The second set of valves, the semilunar valves, each composed of three pocketlike cusps, guards the bases of the two large arteries leaving the ventricular chambers. These are referred to as the pulmonary & aortic semilunar valves. The valve cusps are forced open and flatten against the walls of the artery as the ventricles discharge their blood into the large arteries during systole. However, when the ventricles relax, blood begins to flow backward toward the heart and the cusps fill with blood, closing the valves and preventing arterial blood from reentering the heart.

Questions: 9. What is diastole? ______Systole? ______

10. Explain the umbrella analogy: ______

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Heart Valves (superior view) diagram

CARDIAC CIRCULATION Even though the heart chambers are almost continually bathed with blood, this contained blood does not nourish the myocardium. The functional blood supply of the heart is provided by the right and left , which issue from the base of the aorta, just above the aortic semilunar valve, and encircle the heart in the atrioventricular groove at the junction of the atria and ventricles.

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