Explain the reduced ejection phase of the cardiac cycle, including why aortic and pulmonary artery pressures decrease.

let's explain this part of the cardiac cycle, جدة.

This text describes the changes in aortic and pulmonary artery pressures during the reduced ejection phase of ventricular systole, transitioning towards diastole.

• Why pressures decrease:

  • During the initial part of ventricular ejection, blood is rapidly pushed into the aorta and pulmonary artery, causing their pressures to rise.
  • However, as the ventricles continue to contract, the rate of blood ejection slows down. At this point, the amount of blood being ejected from the ventricles into the great arteries becomes smaller than the amount of blood that is simultaneously flowing out of these arteries into the peripheral smaller vessels.
  • Because more blood is leaving the great arteries than entering them, their overall volume decreases, leading to a decrease in aortic and pulmonary artery pressures.

• Pressure relationship and momentum:

  • Even though the ventricular pressures are also decreasing as the ventricles begin to relax, the aortic and pulmonary artery pressures gradually become slightly higher than the ventricular pressures.
  • Despite this pressure difference, blood flow from the ventricles into the aorta and pulmonary artery continues for a brief moment. This continued flow is due to the momentum of the forward blood flow that was established during the earlier, rapid ejection phase. This momentum helps push the last bit of blood out before the semilunar valves close.