Vessel outline

Vessel outline - Chapter 21: Blood Vessels and Circulation...

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Chapter 21: Blood Vessels and Circulation I. The Anatomy of Blood Vessels, p. 709 There are 5 general classes of blood vessels: 1. Arteries carry blood away from the heart. 2. Arterioles are the smallest branches of arteries. 3. Capillaries are the smallest blood vessels, where diffusion between blood and interstitial fluid takes place. 4. Venules collect blood from the capillaries. 5. Veins return blood to the heart. The Structure of Vessel Walls, p. 709 The walls of arteries and veins have 3 layers which provide strength and control diameter: 1. The tunica intima is the innermost layer, including the endothelial lining and a layer of connective tissue. 2. The tunica media is the middle layer, containing concentric sheets of smooth muscle in loose connective tissue which binds the tunica media to the inner and outer layers. . 3. The tunica externa is the outer layer, made up of connective tissue that anchors the vessel to adjacent tissues. The walls of large vessels contain small arteries and veins (vasa vasorum ) that supply the cells of the tunica media and tunica externa. Arteries, p. 710 The elasticity of arteries allows them to absorb the pressure waves that come with each heartbeat. Contractility of arterial walls allows arteries to change diameter under control of the sympathetic division of the autonomic nervous system. Vasoconstriction is the contraction of arterial smooth muscle by the ANS. Vasodilatation is the relaxation of arterial smooth muscle, enlarging the lumen. Vasoconstriction and vasodilation affect: 1. the afterload on the heart 2. peripheral blood pressure 3. capillary blood flow As blood moves from the heart to the capillaries, arteries gradually change characteristics: from elastic arteries to muscular arteries to arterioles . Elastic arteries (conducting arteries) are large vessels that transport large volumes of blood away from the heart. The tunica media of elastic arteries has a lot of elastic fibers and few muscle cells. The elasticity of these major vessels ( e.g. pulmonary trunk and aorta) evens out the force of the pulse and promotes steady blood flow. Muscular arteries are medium-sized distribution arteries. Most arteries are muscular arteries. The tunica media has more muscle cells than in elastic arteries. Arterioles are small, with very little tunica externa. The tunica media may be incomplete, or have only 1 or 2 layers of muscle cells. The diameters of small muscular arteries and arterioles change in response to sympathetic or endocrine stimulation . More force is required to push blood through a constricted artery than through a dilated one. Since the force opposing blood flow is called resistance (R ), arterioles are also called resistance vessels . If the elastic fibers in the wall of an artery
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This note was uploaded on 12/29/2011 for the course BIOLOGY 24011 taught by Professor Pan during the Fall '11 term at HCCS.

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Vessel outline - Chapter 21: Blood Vessels and Circulation...

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