The semilunar (pulmonary and aortic) valves do which of the following?
a. Cause almost the entire afterload for the ventricles.
b. Consist of two half-moon or cres-cent-shaped cusps.
c. Prevent arterial backflow during ventricu-lar relaxation.
d. Separate the ventricles from their arterial outflow tracts.
ANS: D
A set of semilunar valves separates the ventricles from their arterial outflow tracts (Figure 9-3). Consisting of three half-moon–shaped cusps attached to the arterial wall, these valves prevent backflow of blood into the ventricles during diastole (or when the heart's chambers fill with blood).
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