MCAT Question A Day - 6/12/13 - Answer!
The two sounds associated with the cardiac cycle (“LUBB-dupp”) are heard in sequence when the valves of the heart close during ventricular systole and ventricular diastole, respectively. Which valves produce the first sound?
A. Tricuspid valve and bicuspid valve
B. Pulmonary semi-lunar valve and aortic semi-lunar valve
C. Tricuspid valve and pulmonary semi-lunar valve
D. Bicuspid valve and aortic semi-lunar valve
The correct answer is (A). When the ventricles contract, the A-V valves (tricuspid and bicuspid) close and make the first louder sound: LUBB. This prevents the backflow of blood into the atria, and forces blood through the open semi-lunar valves into the two major arteries. When the ventricles relax, the A V valves open, blood enters the ventricles from the atria, and blood in the aorta and pulmonary arteries backs up slightly—closing the semi-lunar valves and making the second softer sound: dupp.
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