Question

A vein possesses a large lumen because

• A. Tunica media and tunica externa form a single coat
• B. Tunica interna and tunica media form a single coat
• C. Tunica interna, tunica media and tunica externa are thin
• D. Tunica media is a thin coat

Answer 1

Answer: (D)

Basically, each artery and vein consists of three layers: An inner lining of squamous endothelium (the tunica interna), a middle layer of smooth muscle and elastic fibre (the tunica media), and an external layer of fibrous connective tissue with collagen fibres (the tunica externa). The tunica media is comparatively thin in the veins, due to which its lumen increases in size.