QUESTION 2 During ventricular systole, The AV valves are open and the semilunar valves are closed while the ventricle contracts O The AV valves are closed and the semilunar valves are open until sufficient pressure is generated in the ventricle to force the AV valves to close Blood flows passively from the atria and the ventricle fills with no change in ventricular volume O O The aorta and pulmonary arteries are at the mean arterial pressure The AV valves are closed and the semilunar valves are closed until sufficient pressure is generated in the ventricle to force the semilunar valves open
The correct answer and explanation is:
Correct Answer: The AV valves are closed and the semilunar valves are closed until sufficient pressure is generated in the ventricle to force the semilunar valves open.
Explanation
Ventricular systole refers to the contraction phase of the ventricles, which is a critical part of the cardiac cycle. This process can be broken into two main stages:
- Isovolumetric Contraction Phase
At the onset of ventricular systole, the ventricles begin to contract. The pressure inside the ventricles rises sharply. During this time:- The atrioventricular (AV) valves (tricuspid and mitral valves) are closed to prevent backflow of blood into the atria.
- The semilunar valves (aortic and pulmonary valves) are also closed because the pressure in the ventricles is not yet high enough to overcome the pressure in the aorta and pulmonary arteries.
- Since all valves are closed, there is no change in ventricular volume, and the blood is compressed, increasing intraventricular pressure.
- Ventricular Ejection Phase
Once the pressure in the ventricles surpasses the pressure in the aorta and pulmonary arteries:- The semilunar valves open, allowing blood to be ejected from the ventricles into the systemic (aorta) and pulmonary (pulmonary artery) circulation.
- During this phase, the AV valves remain closed to prevent backflow of blood into the atria.
This sequence ensures unidirectional blood flow and efficient circulation. The pressure gradient generated during systole is essential for moving blood through the high-resistance systemic and pulmonary circuits. Proper functioning of the valves is critical; any valve dysfunction can lead to inefficient blood flow and cardiac complications.
In summary, during the initial phase of ventricular systole, the AV valves and semilunar valves are closed until the ventricles generate sufficient pressure to open the semilunar valves and begin ejecting blood. This mechanism demonstrates the precise timing and coordination of the heart’s structure and function.