Layers of Blood Vessel Walls

The tunica intima:

• It is the innermost layer of the arteries and veins. It contains the endothelium,a simple squamous epithelium that lines the lumen of all vessels. Since the endothelium is continuous with the endocardial lining of the heart, it forms a slippery surface that minimizes friction so blood moves smoothly through the lumen.

The tunica media:

• It is the middle layer, is mostly circularly arranged smooth muscle cells and sheets of elastin. The activities of the tunica media are critical in regulating the circulatory system because small changes in vessel diameter greatly influence blood flow and blood pressure.

The tunica externa:

• It is the outer layer of a blood vessel wall, , is mainly composed of collagen fibers that protect the vessel, and attach it to surrounding structures. It contains nerve fibers, lymphatic vessels, and elastic fibers (in large veins).

• In large vessels, the tunica externa contains a structure known as the vasa vasorum, which nourishes the external tissues of the blood vessel wall.

NA. (2013). The Cardiovascular System: Blood Vessels. [Web Portal]. Retrieved from http://anatomyandphysiologyi.com/cardiovascular-system-blood-vessels/