What is the left atrium?

The left atrium is one of the four chambers of the heart. Compared to the right atrium, it is smaller in volume and thickness; however its axis is arranged transversely as to cover part of the right atrium. Oxygen-rich blood from the lungs enters the left atrium through the pulmonary vein. The blood is then pumped into the left ventricle through the mitral valve in order to deliver oxygen-rich blood to all bodily tissues and organs. Mitral valve prolapse is a condition in which the mitral valve between the left atrium and left ventricle fails to close properly. Although it usually does not require treatment, this condition can lead to more serious complications and contacting a doctor may be necessary in some cases.

The heart is an organ that is divided into several parts, which help perform its main function: to carry oxygen-rich blood to the rest of the body (cells, tissues and organs) in order to feed them, and receive carbon dioxide enriched blood to be sent to the lungs, where the oxygen exchange takes place.

It is comprised of two atria and two ventricles. The atria are the two upper chambers of the heart, separated from the atrial septum. As an infant, a small hole in the atrial septum is known as the foramen ovale and it allows blood to flow straight through to the left atrium, bypassing the nonfunctional lungs of fetus, since the baby receives oxygen and nutrients directly from the mother through the placenta. At birth, a thin fibrous tissue moves to cover the foramen ovale and prevent the flow of blood between the atria. This is known as the fossa ovalis. Once born, lungs become necessary and the connection between the two atria closes.

The left and right atria are not symmetrical and differ in location, size and shape. They communicate with the corresponding ventricles, and differ from them in a sense that blood from the ventricles is pushed out of the heart rather than entered into it.


What function does the left atrium serve?

The heart is a pump that is known to carry oxygen-rich blood from the lungs to the cells of tissues and organs, in exchange for carbon dioxide enriched blood that needs to be transformed. The oxygenated blood travels towards organs and tissues in the body through the aorta, the artery that carries nourishment to the whole body and further splits into smaller and smaller branches and capillaries. Carbon dioxide enriched blood returns to the heart through the veins, which transform it to oxygen.

The left atrium is responsible for receiving oxygenated blood, directly from the lungs through the left and right pulmonary veins. When the atria contract (diastole phase), the blood is pumped from the left atrium to the left ventricle through the mitral orifice (also called the bicuspid orifice), which is guarded by the mitral valve (bicuspid valve). Thus, the left atrium is known as the first “station” before oxygen-rich blood and nutrients arrive to the cells and tissues throughout the body through the aorta and its branches.