Internal surface (left atrium, anatomy)
The internal surface of the left atrium is notable for:
- its generally smooth endocardial surface; this is the result of most of the left atrium originating embryologically from the pulmonary veins
- the interatrial septum:
- passes obliquely, posteriorly from right to left across the cavity of the chamber
- often, a lunate depression is visible; this corresponds to the ostium secundum of the developing heart
- the narrow aperture leading to the auricle; as with the right atrial auricle, musculi pectinati line its surface; however, the ridges are less well developed than in the right atrium
- veins entering into the chamber:
- pulmonary veins, typically two on each side entering in the superior part of the chamber; there are no valves at the intersection of each vein with the chamber
- foramina venarum minimarum as in the right atrium
- the atrioventricular orifice:
- inferiorly and anteriorly within the chamber
- smaller than the right atrioventricular orifice
- associated with the mitral valve
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