Parts of the Cardiovascular System Blood Vessel The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from the capillaries back toward the heart. The arteries and veins have three layers, but the middle layer is thicker in the arteries than it is in the veins: 1.Tunica intima (the thinnest layer): a single layer of simple squamous endothelial cells glued by a polysaccharide intercellular matrix, surrounded by a thin layer of subendothelial connective tissue interlaced with a number of circularly arranged elastic bands called the internal elastic lamina. 2.Tunica media (the thickest layer in arteries): circularly arranged elastic fiber, connective tissue, polysaccharide substances, the second and third layer are separated by another thick elastic band called external elastic lamina. The tunica media may (especially in arteries) be rich in vascular smooth muscle, which controls the caliber of the vessel. 3.Tunica adventitia: (the thickest layer in veins) entirely made of connective tissue. It also contains nerves that supply the vessel as well as nutrient capillaries (vasa vasorum) in the larger blood vessels. Capillaries consist of little more than a layer of endothelium and occasional connective tissue. When blood vessels connect to form a region of diffuse vascular supply it is called an anastomosis (pl. anastomoses). Anastomoses provide critical alternative routes for blood to flow in case of blockages. There is a layer of muscle surrounding the arteries and the veins which help contract and expand the vessels. This creates enough pressure for blood to be pumped around the body. Kinds of Veins and Arteries Aorta-the largest artery, carries blood out of the heart Branches of the aorta, such as the carotid artery, the subclavian artery, the celiac trunk, the mesenteric arteries, the renal artery and the iliac artery. Arterioles-smaller arteries Capillaries-smallest blood vessels Venules-very small blood vessel in the microcirculation that allows blood to return from the capillary beds to the larger blood vessels called veins. Venules range from 7 to 50μm in diameter. Veins contain approximately 70% of total blood volume, 25% of which is contained in the venules. Veins-carry blood from capillaries back to the heart Large collecting vessels, such as the subclavian vein, the jugular vein, the renal vein and the iliac vein. Venae cavae-the 2 largest veins, carry blood into the heart
Posted on: Sat, 29 Jun 2013 06:26:03 +0000
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