Anatomy of the heart left atrium
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Assistant Editor(s)-in-Chief: Rim Halaby, Yazan Daaboul
Left Atrium
- The left atrium is the major component of the heart base.
- The interatrial septum is part of the left atrial wall; it runs posteriorly and to the right. Its wall is slightly thicker than that of the right atrium.
- The interior of the left atrium is characterized by two main pouches:
- A larger smooth-walled part, believed to be formed by absorption of parts of embryonic pulmonary veins.
- A smaller muscular auricle with pectinate muscles, believed to be remnant of left part of primordial atrium.
Pulmonary Veins:
- Blood enters the left atrium on the posterior wall via 4 valveless pulmonary veins, arranged in two pairs, left and right.
Left Auricle:
- Similar to the right atrium, the left atrium also contains a left auricle.
- In contrast to the right auricle which overlaps the ascending aorta, the left auricle forms the superior part of the left border of the heart and overlaps the pulmonary trunk.
- The left auricle is a small muscular region containing pectinate muscles inside.
Left Atrio-Ventricular Orifice:
- At the level of the left atrio-ventricular orifice, the outflow of oxygenated blood received from the pulmonary veins evacuates the left atrium.