The left atrium serves as a vessel for blood coming from the lungs and a pump to deliver blood to other parts of the heart, according to Healthline. Oxygen-rich blood from the lungs goes to the left atrium via the pulmonary vein.
The left atrium is one of the heart’s four chambers, and it is found on the left posterior side, says Healthline. It has slightly thicker walls than the right atrium. Once oxygen-rich blood enters the left atrium, the blood is pumped through the mitral valve into the heart’s left ventricle chamber. It is then pumped into the rest of the body to deliver oxygen.
The University of Rochester Medical Center explains that the heart is composed of four chambers; the upper chambers are called atria, while the lower chambers are known as ventricles. Blood goes through a valve before leaving the heart’s chambers. The valves prevent backward blood flow and serve as one-way inlets for blood entering a ventricle and one-way outlets for blood leaving a ventricle. They open and shut as the heart contracts and relaxes, allowing blood to enter the ventricles and atria alternately. The aortic valve closes and the mitral valve opens so that blood flows into the left ventricle from the left atrium. More blood flows in the left ventricle as the left atrium contracts.