During ventricular systole, closure of the atrioventricular (AV) valves coincides with:
A) Atrial chamber filling
B) Aortic valve opening
C) Isovolumetric contraction
D) Semilunar valves opening
Ans: C
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Ventricular systole is divided into two parts: isovolumetric contraction when the AV valves close and ventricles fill; and the ejection period, when the semilunar valves open and blood is ejected through the aortic valve into circulation. Immediately after closure of the AV valves, there is a 0.02- to 0.03-second period during which the pulmonic and aortic valves remain closed. During this period, the ventricular volume remains the same while the ventricles contract, producing an abrupt increase in pressure. At the end of systole, the ventricles relax, causing a precipitous fall in intraventricular pressures. As this occurs, blood from the large arteries flows back toward the ventricles, causing the aortic and pulmonic valves to snap shut—an event marked by the second heart sound.
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