In late diastole (relaxation phase), the semilunar (pocket) valves close, due to decreasing arterial pressure, to prevent blood flowing back into the ventricles. These stay closed during atrial systole. (But open again during ventricular systole.)
Then, as the ventricles contract during ventricular systole, the bicuspid and tricuspid valves close to prevent blood from flowing back to the atria.
So, it really depends on which phase of the contraction we are looking at.
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During systole, both atrioventricular valves (tricuspid and mitral) are closed. The aortic valve is open. During diastole, both atrioventricular valves are open, and the aortic valve is closed.
No, both sets of valves are not closed simultaneously during the cardiac cycle. The atrioventricular valves (mitral and tricuspid) are closed when the ventricles contract (systole), while the semilunar valves (aortic and pulmonic) are closed when the ventricles relax (diastole).
No, both sets of heart valves are not open at the same time during the cardiac cycle. The atrioventricular valves (bicuspid and tricuspid) are open when the ventricles are relaxed (diastole) to allow blood to flow from the atria to the ventricles. The semilunar valves (aortic and pulmonary) are open when the ventricles contract (systole) to allow blood to be ejected into the arteries.
The semilunar valves are open when the ventricles contract during systole, allowing blood to be pumped out of the heart. They close when the ventricles relax during diastole, preventing blood from flowing back into the heart.
During heart contraction
At the end of ventricular systole, the ventricles relax; the semilunar valves snap shut, preventing backflow, and momentary, the ventricles are closed chambers. The aortic semilunar valves snaps shut, a momentary increase in the aortic pressure results from the elastic recoil of the aorta after valves closure.
The AV valves open when the blood pressure exerted on their atrial side is greater than that of the ventricle side. This will happen when blood returning to the heart fills the atria and puts pressure against the valve.
It's called systole, but valve closure is a passive event caused by an attempt at retrograde blood flow.
When a doctor listens to your heart he hears the systole and diastole of the heart. The "lub-dub" that they hear is the closure of valves of the heart at rest (diastole) when the heart fills with blood and the heart squeezes blood (systole) out into the body. When you feel the pulse, you only feel when the heart pushes blood through the vascular system during systole.
The two semilunar valves are the aortic valve and the pulmonic valve. The aortic valve opens when the left ventricle contracts, allowing blood to pass into the aorta. The pulmonic valve opens when the right ventricle contracts, allowing blood to pass into the pulmonary artery.
The lub is caused by the closing of the AV valves. The dup is caused by the semilunar valves closing at the end of systole.
The first heart sound "lub" is caused by the closing of the mitral and tricuspid valves during the beginning of systole (ventricular contraction). The closure of these valves creates vibrations in the surrounding fluid and tissues, resulting in the characteristic sound.