Select all of the TRUE statements on the ventricular pressure-volume relationship:
A.Ventricular pressure exceeds atrial pressure during ejection
B. Filling occurs during ventricular systole
C. Increased preload results in decreased stroke volume
D. Atrial pressure is greater than ventricular pressure during filling
E. Preload is set by the end-diastolic volume
F.The AV and aortic valves are both closed during the isovolumetric phases
The correct answer and explanation is:
The correct true statements are:
- A. Ventricular pressure exceeds atrial pressure during ejection
- D. Atrial pressure is greater than ventricular pressure during filling
- E. Preload is set by the end-diastolic volume
- F. The AV and aortic valves are both closed during the isovolumetric phases
Explanation:
A. Ventricular pressure exceeds atrial pressure during ejection
During the ejection phase of the cardiac cycle, the ventricle contracts, generating high pressure to overcome the pressure in the aorta and pulmonary artery. This pressure is higher than the atrial pressure, which is why the atrioventricular (AV) valve is closed during systole.
D. Atrial pressure is greater than ventricular pressure during filling
During the filling phase (diastole), the ventricles relax, causing the pressure inside the ventricles to drop. Since the atria are still receiving blood from the veins, their pressure is higher than that of the ventricles. This pressure difference causes the AV valves to open, allowing blood to flow into the ventricles.
E. Preload is set by the end-diastolic volume
Preload refers to the stretch of the myocardial fibers at the end of diastole, which is determined by the end-diastolic volume (EDV). The more blood that fills the ventricles, the greater the stretch of the heart muscle fibers, which influences the force of contraction (Frank-Starling mechanism).
F. The AV and aortic valves are both closed during the isovolumetric phases
The isovolumetric contraction phase (early systole) and isovolumetric relaxation phase (early diastole) both involve the closure of the AV valves and aortic valves. During these phases, the ventricles are not yet ejecting or filling blood, so there is no change in ventricular volume despite changes in pressure.
Incorrect Statements:
B. Filling occurs during ventricular systole
Filling of the ventricles occurs during diastole, not systole. During systole, the ventricles are contracting and ejecting blood into the arteries.
C. Increased preload results in decreased stroke volume
This statement is incorrect. According to the Frank-Starling mechanism, an increase in preload (end-diastolic volume) leads to an increase in stroke volume because greater filling of the ventricles leads to a stronger contraction.