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BIOB34H3 (271)
Ted Petit (35)

Chapter 20.docx

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Biological Sciences
Ted Petit

Chapter 20 Blood Vessels • General Pattern - heart → arteries → arterioles → capillaries → venules → veins → heart • Basic Structure - Three tunics surrounding a lumen 1. tunica intima a. endothelium- slick surface reduces friction b. basement membrane c. elastic lamina 2. tunica media a. smooth muscle and elastin sheets b. regulates circulation by vasoconstriction or vasodilation 3. tunica externa a. collagen and elastin fibers protect vessel and anchor it to other structures b. larger vessels have their own blood vessels to supply outer tissues (called vasa vasorum) • Arteries - Carry blood away from heart - Withstand high pressure - Three groups 1. elastic arteries (conducting) a. aorta and major branches b. large (1 - 2.5 cm in diameter) c. lots of elastin allows expansion and recoil (recoil keeps blood moving between heartbeats) 2. muscular arteries a. deliver blood to specific body organs b. .3 mm – 1 cm in diameter c. more smooth muscle, less elastin d. active in vasoconstriction 3. arterioles a. 10 m - .3 mm in diameter b. larger ones have all three tunics c. smaller ones are just smooth muscle surrounding endothelium - Anastomoses 1. most tissues receive blood from more than one artery 2. anastomoses are branches between arteries 3. also occur between veins 4. called collateral circulation (allows alternate pathways for blood flow) • Capillaries - Smallest vessels, 3 – 10 m in diameter - Thin tunica intima only - Allow exchanges between blood and tissues - Near almost all cells (epithelial sheets, cartilage, some parts of eye have none) - Varying distribution based on need 1. e.g., muscles, liver, kidneys, lungs, and nervous system have lots - Types 1. continuous a. tight junctions b. small gaps called intercellular clefts allow fluids and small solutes to pass c. most common type 2. fenestrated a. some cells have "windows" covered with a thin membrane b. greater permeability to fluids and solutes c. found where absorption or filtration needed (small intestine, endocrine glands, kidney) 3. sinusoidal a. very "leaky" with fenestrations and large intercellular clefts b. allows relatively large molecules to pass c. found in liver, bone marrow, lymphoid tissues, some endocrine glands - Capillary beds 1. network of capillaries that feeds tissues 2. parts a. terminal arteriole feeds bed b. metarteriole c. true capillaries (have precapillary sphincters that regulate blood flow) d. thoroughfare channel e. postcap
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