Closed Circulation Basics

A closed circulation is a heart-pump and its blood vessels: arteries, arterioles, capillaries and veins. Blood circulates inside a closed system and rarely leaves the vessels. Arteries convey blood away from the heart to capillary beds, and veins convey blood back to the heart from the capillaries. Arterioles are stopcocks interposed between arteries and capillaries. The nervous system opens and closes the stopcocks. Acting together, these valves aided by the beat of the heart maintain central blood pressure in the arteries of the circulation, but individually, each stopcock drops the perfusion pressure in the capillaries and controls how much blood runs off into the capillary beds of its region.

In seventy years, your heart beats around 2,759,400,000 times (75 beats per minute) squeezing 400 million liters of blood around your circulation. Your circulation matches nutrients and oxygen to what your cells need, while at the same time, your circulation removes wastes, regulates your body temperature, and distributes hormones.

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