||It has been suggested that this article be merged into Atrium. (Discuss) Proposed since August 2014.|
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Anterior (frontal) view of the opened heart. White arrows indicate normal blood flow.
|Artery||circumflex branch of left coronary artery|
|Vein||oblique vein of the left atrium|
The left atrium is one of four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve. Atria facilitate circulation primarily by allowing uninterrupted venous flow to the heart, preventing the inertia of interrupted venous flow that would otherwise occur at each ventricular systole.
In the developing fetus there is an oval opening, the foramen ovale (heart) between the atria which normally closes at birth. If this does not close it could result in a hole in the heart, an atrial septal defect. In the fetus, the right atrium pumps blood into the left atrium, bypassing the pulmonary circulation (which is not needed in the fetus).
High in the upper part of the left atrium is an ear-shaped muscular pouch, the left atrial appendage (LAA). This is also called the auricle with reference to its shape. The atria themselves were previously called the auricles.
The left atrium receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve. The atria facilitate circulation primarily by allowing an uninterrupted venous flow to the heart, preventing the inertia of interrupted venous flow that would otherwise occur at each ventricular systole.
The left atrial appendage appears to "function as a decompression chamber during left ventricular systole and during other periods when left atrial pressure is high".
|BSA, body surface area|
In an adult, an atrial septal defect would result in the flow of blood in the reverse direction - from the left atrium to the right - which will reduce cardiac output, potentially causing cardiac failure and in severe or untreated cases cardiac arrest and sudden death.
In patients with atrial fibrillation, mitral valve disease, and other conditions, blood clots have a tendency to form in the LAA. Blood clots caused by atrial fibrillation stem from the LAA in more than 90% of cases. They may dislodge (forming emboli), which may lead to ischemic damage to the brain, kidneys, or other organs supplied by the systemic circulation. Left atrial appendage occlusion is an experimental treatment to prevent stroke in atrial fibrillation.
The left atrial appendage can serve as an approach for mitral valve surgery. The left atrial appendage can be seen on a standard posteroanterior x-ray, where the lower level of the left hilum becomes concave.
Many other animals, including mammals, also have four-chambered hearts, which have a similar function. Some animals (amphibians and reptiles) have a three-chambered heart, in which the blood from each atrium is mixed in the single ventricle before being pumped to the aorta. In these animals, the left atrium still serves the purpose of collecting blood from the pulmonary veins.
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