Which statement best describes the tunica media?

Which statement best describes the tunica media?

• A. It is the outermost layer of a blood vessel.
• B. It is the layer that thickest in arteries and contains smooth muscle.
• C. It lines the lumen and secretes anticoagulants.
• D. It is the site of gas exchange.

Answer: (B)

The tunica media is the middle layer of a blood vessel, made mainly of smooth muscle arranged in a circular pattern. This muscular layer lets vessels constrict or dilate, which controls blood flow and pressure. In arteries, it’s the thickest layer, providing the strength to withstand high pressure and the ability to regulate peripheral resistance; elastic fibers within it also help the vessel recoil after each heartbeat. It isn’t the outermost layer (that’s the adventitia) and it isn’t the lining that secretes anticoagulants (that function belongs to the endothelium of the inner tunica intima). Gas exchange occurs in capillary walls, not in the tunica media.

The tunica media is the middle layer of a blood vessel, made mainly of smooth muscle arranged in a circular pattern. This muscular layer lets vessels constrict or dilate, which controls blood flow and pressure. In arteries, it’s the thickest layer, providing the strength to withstand high pressure and the ability to regulate peripheral resistance; elastic fibers within it also help the vessel recoil after each heartbeat. It isn’t the outermost layer (that’s the adventitia) and it isn’t the lining that secretes anticoagulants (that function belongs to the endothelium of the inner tunica intima). Gas exchange occurs in capillary walls, not in the tunica media.