A histological specimen of spleen shows a vessel with a wall consisting of endothelium and subendothelial layer, median membrane is absent, exterior membrane inosculates with the layers of spleen connective tissue. What vessel is it?

Answer options

1. Artery of muscular type
2. Arteriole
3. Vein of non-muscular type
4. Capillary
5. Vein of muscular type

Explanation

The walls of veins have three layers, or coats: an inner layer, or tunica intima; a middle layer, or tunica media; and an outer layer, or tunica adventitia. The tunica intima differs from the inner layer of an artery: the elastic membrane lining the artery is absent in the vein, which consists primarily of endothelium and scant connective tissue. The tunica media, which is an artery is composed of muscle (for muscular artery) and elastic fibers (for elastic artery), is thinner in a vein and contains less muscle and elastic tissue. Muscles are absent in the case of non-muscular veins. The outer layer (tunica adventitia) consists chiefly of connective tissue and is the thickest layer of the vein. This is less an artery.