IMG_0018 - towards heart closing semilunar valves The...

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Phases of the Cardiac Cycle 1. Yentnicular filling - from mid to late diastole when heart chambers are relaxed. a) blood flows passively into atria and through the open AV valves into ventricles. b) atria contract forcing the remainder of the blood into ventricles. 2. Ventricular systole - includes isovolumetric contraction and ventricular ejection. a) as ventricles contract, intraventricular pressure rises closing AY valves. Ventricles are closed completely for a brief period : isovolumetric contraction phase. b) ejection: the rising ventricular pressure forces the semilunar valves to open. Blood is ejected into the pulmonary trunk and aorta. 3. Isovolumetric relaxation - occurs during early diastole. Ventricles relax and ventricular pressure decreases. Blood in aorta and pulmonary trunk backflow
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Unformatted text preview: towards heart closing semilunar valves. The ventricles are totally closed off again in this relaxation phase. Atrial filling The atria have been filling with blood. When the pressure exerted by the blood on the atrial side ofthe AV valves exceeds that ofthe ventricles below, the AV valves are forced open and the ventricular filling phase begins again. (Both atria contract at the same time and both ventricles contract at the same time) Therefore, blood flow is controlled by pressure changes: 1. Pressure changes reflect the contractions and relaxations ofthe heart. 2. Blood moves from higher to lower pressure (pressure gradient) 3. Pressure changes cause the valves to open and close which keeps blood flowing in the forward direction. 9r...
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