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Left Atrium
Cardiovascular System

Left Atrium

Atrium sinistrum

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Morphology/Structure

The left atrium is approximately cube shaped and forms the base of the heart posteriorly. It has thicker muscular walls compared to the right atrium; however, the ventricular walls are significantly thicker. The inner surface contains pectinate muscles, but unlike the right atrium, it does not contain the crista terminalis.

The left atrium has an appendage called the auricle, which is longer in comparison to the right auricle. However, it's narrower, and its pectinate muscles are smaller.

There are four openings for the pulmonary veins, the superior and inferior pulmonary veins on the right and left side. These form the majority of the atrial wall. Occasionally, there is a common pulmonary vein on the left. The right pulmonary veins sit posterior the superior and inferior venae cavae, respectively.

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Key Features/Anatomical Relations

The atria are separated by the interatrial septum. The rough-walled septum contains a shallow concavity with a surrounding ridge, thus marking the floor of the floor of the fossa ovalis and the valve of the oval fossa (or limbus fossa ovalis), respectively. The smoother circumferential area that surrounds the orifice of the atrioventricular valve is called the vestibule.

Externally, the interatrial sulcus (groove of Waterson) divides the two atria. The coronary sulcus (atrioventricular sulcus) divides the atria above from the ventricles below and contains the main limbs of the coronary arteries, as well as the coronary sinus, which marks the confluence of the cardiac veins.

Additionally, the left atrium forms the anterior aspect of the oblique pericardial sinus.

Function

The left atrium receives oxygenated blood from the lungs via the pulmonary veins during ventricular systole. Blood is squeezed out of the atrium during atrial systole, passing through the left atrioventricular valve into the left ventricle.

List of Clinical Correlates

- Atrial septal defect

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Left Atrium

ScienceDirect image

The posterior LA is a smooth, thin-walled structure that nearly always directly overlies the esophagus.

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