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Left atrium

Definition, function and anatomy of the left atrium.

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Hey, everyone! This is Matt from Kenhub, and in this tutorial, we will talk about the left atrium of the heart.

The atria of the heart, which are known singularly as an atrium, are a pair of blood collecting chambers that comprise two of the four chambers of the heart.

The main function of the atria is to facilitate circulation by rhythmically contracting and relaxing their walls, pushing the blood that is returned to them via the major venous vessels during ventricular systole into the ventricles.

In this tutorial, we will focus on the left atrium.

The left atrium, as seen here, highlighted in green, on the diaphragmatic surface of the heart, is responsible for collecting the outflow of oxygenated blood that runs back to the heart from the pulmonary veins. It passes this volume of blood onto the left ventricle as the atrium contracts and the mitral valve opens.

The mitral valve is also known as the bicuspid valve because it is formed by two septal cusps. Occasionally, it is also mentioned in literature as the left atrioventricular valve. The blood supply to the left atrium is governed by the left circumflex coronary artery, and it is drained by the oblique vein of the left atrium, which arises during embryonic development from the left side of the fetal superior vena cava.

The main anatomical structure of note is the foramen ovala, which is a foramen within the atrial walls that allows blood to shunt between the two atria during embryonic development. Normally, around the time of birth, this hole in the cardiac wall closes. Otherwise, it is known as a congenital heart defect named patent foramen ovale. It is not, however, generally problematic in child or adulthood.

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