Veins are the other type of major blood vessel and are responsible for carrying blood towards and into the heart, in order to become oxygenated. Veins operate under lower pressure than arteries and do not possess the same elasticity that arteries do. Veins transport unoxygenated blood as opposed to arteries which carry oxygenated blood. Veins, like arteries, have lumens, but they are comparably wider than the lumens of arteries. Veins are composed of venues, which are tiny blood vessels that pull blood from capillaries into the actual vein. Veins are actually composed of three tissue layers but are less elastic than the walls of arteries.
The regulation of blood flow during exercise is governed by the demands of the muscle tissue being used. Certainly, when an individual is exercising, the heart rate increases as a response to the body’s immediate need for larger amounts of oxygenated blood. The body’s blood flow rate can increase during exercise by as much as 20 times more than what it is at rest. During periods of exercise, all of the body’s capillaries are opened and in use versus the mere ¼ of the body’s capillaries which are used at rest.
During periods of exercise, the body experiences what is called low oxygen tension. This is a result of the use of multiple muscular groups during periods of heavy activity. In addition, vasodilators are released as the demand for oxygenated blood throughout the body increases, “Low oxygen tensions resulting from greatly increased muscular activity or the release of vasodilator substances such as lactic acid, carbon dioxide, and potassium ions causes dilation of precapillary sphincters. Increased sympathetic stimulation and epinephrine released from the adrenal medulla cause some vasoconstriction.