Answer to Question #58387 in Human Anatomy and Physiology for sue

Question

The opening and closing of the heart valves is caused by:

a. action potentials acting on the valve cusps

b. contraction of smooth muscle cells at the base of the valves

c. contraction and relaxation of papillary muscles

d. pressure changes during the cardiac cycle

e. magic elves and pixies

Answer 1

d. pressure changes during the cardiac cycle

The opening and closing functions of the valves are controlled by pressure differences generated within the heart. When the atrioventricular valves (tricuspid and mitral) are open, during blood flow to the ventricles, the semilunar valves are closed to prevent backflow into the ventricles. When the ventricular pressure is greater than the atrial pressure the tricuspid and mitral valves will shut. When the ventricles contract the pressure forces the semilunar aortic and pulmonary valves open. As the ventricles relax the semilunar valves will close in response to decreased pressure.