Afterload is the pressure threshold that must be exceeded to open _______.

Afterload is the pressure threshold that must be exceeded to open _______.

• A. The mitral valve
• B. The aortic semilunar valve
• C. The tricuspid valve
• D. The aortic and pulmonary semilunar valves

Answer: (D)

Afterload is the pressure the ventricle must generate to overcome the pressure in the outflow tract to open the valve and eject blood. The valves that set this threshold are the semilunar valves—the aortic valve on the left ventricle and the pulmonary valve on the right. These valves open only when ventricular pressure exceeds the arterial pressure beyond them. The mitral and tricuspid valves control filling and open when atrial pressure exceeds ventricular pressure, so they aren’t governing afterload. Therefore, the pressure threshold to open both semilunar valves fits the concept of afterload.

Afterload is the pressure the ventricle must generate to overcome the pressure in the outflow tract to open the valve and eject blood. The valves that set this threshold are the semilunar valves—the aortic valve on the left ventricle and the pulmonary valve on the right. These valves open only when ventricular pressure exceeds the arterial pressure beyond them. The mitral and tricuspid valves control filling and open when atrial pressure exceeds ventricular pressure, so they aren’t governing afterload. Therefore, the pressure threshold to open both semilunar valves fits the concept of afterload.