Anatomy of the heart left atrium

Left atrium is located at the base of the heart above the left ventricle. It receives oxygenated blood through pulmonay veins and pumps the blood to the left ventricle through the mitral valve.

• 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.

• Blood enters the left atrium on the posterior wall via 4 valveless pulmonary veins, arranged in two pairs, left and right.

• 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.

• At the level of the left atrio-ventricular orifice, the outflow of oxygenated blood received from the pulmonary veins evacuates the left atrium.

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