Identify The Three Different Layers Of The Tunica Externa

At the point when blood streams from the heat it travels through blood vessels. There are five fundamental types of blood vessels: arteries, arterioles, capillaries, venules, and veins. There are three basic layers of a blood vessel: tunica interna, tunica media, and tunica externa. The inner lining of a blood vessel that comes into direct contact with blood is the tunica inerna. In this layer blood flows through the blood vessel in a tube that forms, this tube is called the lumen. There are three layers of the tunica interna: the innermost layer is called endothelium, the next layer is called the basement membrane which provides support for the epithelial layer which is made from collagen fibers and has tensile strength. This gives flexibility
The openings permit materials to move between the tunica interna to the tunica media. The center layer is the tunica media which is made from muscular and connective tissue. Smooth muscle cells in this layer wrap around and helps regulate the diameter of the lumen, which regulates blood flow through the blood vessel. Separating the tunica media and the tunica externa is a system of elastic fibers called the external elastic lamina. Tunica externa is the outer most layer of the blood vessel which contains elastic and collagen fibers and contains numerus nerves and vessels that supply blood to the wall of a vessel. Arteries is the first of the five blood vessels which have three types of arteries: elastic arteries, muscular arteries and anastomoses. Out of the three elastic arteries are the largest blood vessel in the human body. The aorta and the pulmonary trunk are the two main trunks of elastic arteries. Also there are four major branches of elastic arteries: brachiocephalic, subclavian, common carotid, and common iliac. Elastic arteries help propel blood onward. Contractions push the blood forward allowing elastic arteries to move blood
The last arteries are anastomoses which have more than one artery supplying body regions with blood and provide alternative routes for blood flow to reach body organs. Next are arterioles which are microscopic vessels that control the blood streaming into capillaries. Metarteriole are the end of arterioles. At the metarteriole junctions muscle cells form precapillary sphincters, smooth muscle of the arterioles causes vasoconstriction and increases resistance, which decreases blood flow into capillaries. Third of the blood vessels is capillaries, which are the smallest blood vessels and form an extensive network of branched, interconnecting vessels. Blood flows from capillaries into postcapillary venules. Capillaries main function is to exchange substances from blood and interstitial fluid. They are located near almost every cell in the body and lack tunica media and tunica externa. Venules are the fourth kind of blood vessels whose main function is to receive blood from capillaries and start flowing blood back to the heart. blood flows from capillaries to postcapillary