Answer:
1.The period during which a heart chamber is contracting is called systole.
2. The period during which a heart chamber is relaxing is called diastole.
3. During ventricular contraction, the AV valves (tricuspid and mitral valves) are closed.
4. During ventricular relaxation, the AV valves are open.
5. The pulmonary and aortic valves open when the pressure in the ventricles exceeds the pressure in the pulmonary trunk and aorta.
6. The first sound of a cardiac cycle occurs when the atrioventricular valves are closing.
7. The second sound of a cardiac cycle occurs when the semilunar valves are closing.
Explanation:
We can divide the heart cycle into two parts the systole and the diastole. The systole happens when the heart walls contract, and the diastole when these relax.
The relaxation and contraction allow the flow of blood into the different heart chambers.
During diastole, blood flows to the right atrium from the vena cavae superior and inferior, and the coronary veins and to the left atrium from the pulmonary veins. The blood accumulated in the atriums causes the AV valves to open, and blood flows to the ventricles. In this part, the atrium pressure exceeds the ventricular pressure allowing the blood's flow. When the atriums contract, the remaining blood that was in them, goes to the ventricles. Throughout all this process, the pulmonary and aortic valve is closed due to a pressure difference.
During ventricular systole, there are two phases. First, the ventricles contracts themselves, and the ventricular pressure increases, being higher than the atrium pressure. As a consequence, the AV valves close. During this first phase of contraction, there is not enough pressure to open the pulmonary and aortic valves. In the second phase, the ventricles completely contract themselves, the ventricular blood pressure increases. It becomes higher than the pressure in the aortic and pulmonary valves. As a consequence, the blood pushes the valves open, and blood goes out of the heart. Then, the difference in pressure between the ventricles and the pulmonary trunk and aorta causes the valves in these areas to close.
The first sound that we listen to is the S1 and is during the ventricular contraction that closes the atrioventricular valves. The second sound is the S2, and it happens when the semilunar valves close, also knowns as aortic and pulmonary valves. S2 occurs during diastole once that the blood is out of the ventricle and the contraction has finished.
