MICROANATOMY

Detailed explanation-1: -The middle layer, the tunica media, is primarily smooth muscle and is usually the thickest layer. It not only provides support for the vessel but also changes vessel diameter to regulate blood flow and blood pressure.

Detailed explanation-2: -Blood vessels contain only smooth muscle cells. These muscle cells reside within the tunica media along with elastic fibers and connective tissue.

Detailed explanation-3: -The tunica media is composed chiefly of circumferentially arranged smooth muscle cells. Again, the external elastic lamina often separates the tunica media from the tunica adventitia. Finally, the tunica adventitia is primarily composed of loose connective tissue made up of fibroblasts and associated collagen fibers.

Detailed explanation-4: -The middle layer, the tunica media, is the thickest part of the wall. It consists of mostly smooth muscle and is innervated by the sympathetic nervous system. This sympathetic nervous system is what causes venospasms following changes in temperature or irritation within the vein (11, 12).