What keeps the atrioventricular (AV) valves from being pushed open as the ventricles contract? Pressure of blood pushing against the valves. Contraction of the atria. Closure of the semilunar valves. Contraction of papillary muscles and tightening of chordae tendineae.
The heart is responsible for pumping enough blood to provide the brain and other internal organs with a constant supply of oxygen and other nutrients. Blood, from the other parts of the body, enters into the right atrium and eventually flows into the right ventricle, which is forced into the lungs' pulmonary arteries to be purified. After receiving oxygen, the blood from the lungs flows back to the heart via the pulmonary veins to reaches the left atrium and flows into the left ventricle. After exiting the left ventricle, the blood is out via the aorta to supply the body's tissues.
Both right and left atria are activated and contract to force blood from them into their respective ventricles. Then, the ventricles contract to drive the blood out of it to the other blood vessels that supply the body parts.
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