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15 Cv Cycle - CARDIAC CYCLE page 1 AC Brown A7b HEART AS A...

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CARDIAC CYCLE AC Brown page 1 A7b HEART AS A PUMP A. Functional Anatomy of the Heart 1. Two pumps, arranged in series a. right heart : receives blood from the systemic circulation (via the great veins and vena cava) and pumps blood into the pulmonary circulation (via the pulmonary arteries) b. left heart : receives blood from the pulmonary circulation (via the pulmonary veins) and pumps blood into the systemic circulation (via the aorta) 2. Chambers: each side has two chambers a. atrium : receives blood from the veins and ejects blood into the ventricle through an A-V (atrio-ventricular) valve b. ventricle : receives blood from the atrium and ejects blood into the arterial system through a semilunar valve (ventricles responsible for most of the pumping action of the heart) 3. Valves AV Semilunar right tricuspid pulmonic left mitral aortic broad smaller low resistance resist high back pressure Note: The left and right sides of the heart must pump exactly the same volume of blood when averaged over a period of time
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CARDIAC CYCLE AC Brown page 2 A7b HEART AS A PUMP (continued) B. Imparting Energy to the Blood 1. Mechanism: longitudinal shortening of myocardial fibers compresses blood in the chamber, raising pressure and causing ejection R = right ventricle (thin free wall) L = left ventricle (thick walls) S = intraventricular septum C. Valve and Papillary Muscle Function 1. Role of the valves a. impart a direction to the circulation by closing when downstream pressure exceeds upstream pressure, thus preventing backward regurgitation Note: a valve that permits regurgitation is termed incompetent or insufficient b. present a low resistance to forward flow by opening when upstream pressure exceeds downstream Note: a valve that cannot open completely and therefore presents
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