Question

multiple choice question
valves that direct blood towards the heart are formed by infoldings of which layer of the vein wall?
tunica media
tunica externa
tunica interna
external elastic lamina

Explanation:

To solve this, we recall the structure of vein walls. Veins have three layers: tunica interna (intima), tunica media, and tunica externa. The valves in veins (which direct blood toward the heart) are formed by infoldings of the tunica interna (the innermost layer, also called tunica intima), which is made of endothelium and a subendothelial layer. Tunica media is the middle layer with smooth muscle, tunica externa is the outer connective - tissue layer, and external elastic lamina is part of artery structure (or between layers in some vessels, not related to vein valves).

Answer:

C. Tunica interna