is the tricuspid valve (atrioventricular valve of the heart) closed during rapid filling of the ventricles?
The bicuspid valve is the left atrioventricular valve, and the tricuspid valve is the right atrioventricular valve. Blood enters the heart via the Superior Vena Cava (and Inferior Vena Cava) into the Right Atrium. In between the Right Ventricle and the Right Atrium is the Tricuspid Valve. The right ventricle receives oxygenated blood from the right atrium (as it contracts). Once the ventricles are full, they contract and the tricuspid valve shuts and the pulmonary valve opens. This makes sense for the tricuspid valve to shut (preventing regurgitation or backwash) while the blood flows through the open pulmonary valve into the pulmonary artery (to the lungs.) I would not have chosen a) or c) for an answer. You can rule out b) for an answer because the papillary muscles contract opening the tricuspid valve. You chose the correct answer, d) because once the ventricles are full they contract causing their respective valves to shut.
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