Final answer:
The small left auricle of the heart is derived from the primitive atrium and is a thin-walled extension that contains pectinate muscles, giving it a textured interior. It assists in heart blood flow by acting as a reservoir for blood entering the left atrium.
Step-by-step explanation:
Development of the Left Auricle
The small left auricle, known as the left atrial appendage, is derived from the primitive atrium portion of the primitive heart tube during embryonic development. This structure, along with the right auricle, arises from the fusion of two endocardial tubes. The left auricle is a thin-walled, ear-like extension near the superior surface of the heart. It possesses pectinate muscles within its walls, which are muscle ridges that resemble a comb. The texture of these muscles provides a rougher surface compared to the mostly smooth interior of the left atrium itself. These pectinate muscles are not found elsewhere in the left atrium, only in the auricle.
The pulmonary arteries, which include the left and right branches of the pulmonary trunk, carry deoxygenated blood from the heart to each of the lungs. After the blood is oxygenated in the lungs, it returns to the left atrium via the pulmonary veins. The structure and function of the left auricle play a role in the heart's blood management, acting as a reservoir that allows blood to empty into the left atrium, helping to fill the left ventricle during the heart cycle.