Question

Put the steps of the cardiac cycle into the correct order, starting with the beginning of the cardiac cycle. isovolumetric contraction ventricular ejection atrial contraction and ventricular filling isovolumetric relaxation atrial relaxation and ventricular filling

Answer 1

Answer:

1. Isovolumetric contraction.
2. Ventricular ejection.
3. Isovolumetric relaxation.
4. Atrial relaxation and ventricular filling (passive mechanism).
5. Atrial contraction and ventricular filling (active mechanism)

Explanation:

The cardiac cycle is a continuous pattern of events that occurs so that blood is pumped by the body, in our cardiovascular system. It consists of four stages that occur in the interval of a beat, including cardiac systole and diastole.

This cycle occurs as follows:

• Isovolumetric contraction: Atrioventricular and semilunar valves remain closed. At that point the ventricles begin to contract and, although the ventricular myocardial fibers shorten just a little, the intraventricular pressure increases rapidly. It should be noted however that during this stage, despite several cardiac changes, the ventricular blood volume remains the same.

• Ventricular ejection: During ventricular ejection the semilunar valves are opened, and the atrioventricular valves remain closed. This is because the pressure in the ventricles exceeds the pressure in the arterial trunks and the valves are forced open. The pressure in the left ventricle exceeds the aortic pressure by about 80 mmHg, and the pressure in the right ventricle does the same with the pressure of the pulmonary artery by 10 mmHg.

• Isovolumetric relaxation: During isovolumetric relaxation, which is the penultimate phase of the cardiac cycle, all cardiac valves close. This means that there is no blood passing between the cardiac chambers or out of the heart. The pressure drops below 120 mmHg as the ventricles relax, causing the semilunar valves to close. As the pressure continues to drop, the atrial pressure overcomes that of the ventricles, and the atrioventricular valves open. Meanwhile, blood is being pumped around the body.

• Ventricular filling (atrial relaxation - atrial contraction): Finally, ventricular filling is the final stage of the cardiac cycle. As the name says, this phase is when the ventricles begin to fill with blood coming from the atria, meaning that the semilunar valves are closed and the mitral and tricuspid valves are open. The ventricles are relaxed and are filled to approximately seventy percent of their maximum capacity.

Answer 2

The correct order of the cardiac cycle is:

1. Isovolumetric contraction.
2. Ventricular ejection.
3. Isovolumetric relaxation.
4. Atrial relaxation and ventricular filling (passive mechanism).
5. Atrial contraction and ventricular filling (active mechanism).