The circulatory system is the complex network responsible for delivering nutrients, hormones, and gasses such as oxygen to the body's cells. This system, also known as the cardiovascular system, works in tandem with other systems in the body to maintain homeostasis -- the body’s ability to maintain stability despite constantly changing -- and is integral to many of the functions that allow the body to thrive. The essential parts of the circulatory system are the blood, blood vessels, and the heart, though many secondary components help keep the system working.
For the sake of explanation, educators often state that the circulatory system "begins" in the right atrium. In actuality, if the body functions properly, the system doesn’t start or end anywhere. Each part of the system is working at the same time. The right atrium in the upper-right portion of the heart receives deoxygenated blood through two large veins. The superior vena cava accepts blood from parts of the body such as the head and the arms. The inferior vena cava accepts blood from the legs and lower abdomen.
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