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The right atrium, also known as the right auricle, is one of four chambers of the mammalian heart. Also including the left atrium and the right and left ventricles, the heart functions as a two-pump system, with the right and left sides cycling blood from the body to the lungs and back out to the body in a closed loop. The right atrium receives blood from the body that has been stripped of oxygen, which it then pumps into the right ventricle below and subsequently out of the heart to the lungs for re-oxygenation. The atrium’s contribution to what is known as the pulmonary circuit ensures that deoxygenated or “used” blood is not sent back into the body without first receiving the oxygen the body’s tissues need to survive.
In the human circulatory system, the heart, lungs, and blood vessels work together to deliver blood carrying oxygen and nutrients like glucose throughout the body’s systems. All tissues and structures, from muscles and tendons to joints and organs, depend on the circulatory system to some degree to continue to function properly. In this closed circuit, blood oxygenated in the lungs is sent by the paired pulmonary veins to the left side of the heart, which pumps it out for delivery to the body. The portion of the loop in which blood sent out of the heart is distributed throughout the body, drained of oxygen, and sent back to the heart for re-oxygenation in the lungs is known as the systemic circuit.
A separate pump system on the right side of the heart takes blood deposited by the superior and inferior vena cava, the veins that return deoxygenated blood to the heart, into the right atrium. This blood is pumped through a valve known as the tricuspid valve into the right ventricle below. From here, it is sent through the pulmonary semilunar valve into the paired pulmonary arteries, which carry the blood to the lungs to receive oxygen. The blood is then cycled back into the left atrium by way of the pulmonary veins. The pulmonary circuit, as it is called, ends when the re-oxygenated blood leaves the left side of the heart via the aorta, initiating the systemic circuit once again.
As the right atrium is the space in which a set volume of blood collects before the cardiac muscle pumps it into the ventricle, it is built to function as a holding chamber. With a larger volume than the left atrium and thin, expandable walls, it can hold 60 milliliters of blood. In addition, the surface of these walls is largely rough, corrugated by the pectinati, muscles that contribute to heart contraction.