The heart is the organ that drives the circulatory system. In humans, it consists of four chambers with two that collect blood called atria and two that pump blood called ventricles. The heart's valves prevent blood pumped out of the ventricles from flowing back into the heart.
What prevents blood pumped out of the ventricles from flowing back into the heart?
atria |
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valves |
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capillaries |
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platelets |