AP BIOLOGY

Detailed explanation-1: -The tunica media or a middle layer composed of elastic and muscular tissue which regulates the internal diameter of the vessel. The tunic intima or an inner layer consisting of an endothelial lining which provides a frictionless pathway for the movement of blood.

Detailed explanation-2: -The tunica media is the middle portion of the vessel wall and contains smooth muscle cells and connective tissue, whereas the tunica adventitia is composed of connective tissue that is often continuous with the surrounding soft tissues.

Detailed explanation-3: -The tunica media is the thickest layer of the arterial wall and is composed of elastic fibers, SMCs, fibroblasts and extracellular matrix.

Detailed explanation-4: -Contraction and relaxation of the circular muscles decrease and increase the diameter of the vessel lumen, respectively. Specifically in arteries, vasoconstriction decreases blood flow as the smooth muscle in the walls of the tunica media contracts, making the lumen narrower and increasing blood pressure.

Detailed explanation-5: -tunica media-This is the middle layer of the blood vessel consisting of smooth muscle collagen, and elastic fibers. It is particular prominent in arteries although less obvious in veins and non-existent in capillaries.