Ch21NotesFall10

Ch21NotesFall10 - Ch. 21 Blood Vessels and Circulation The...

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1 Ch. 21 – Blood Vessels and Circulation Arteries – carry blood away from the heart – They are higher pressure vessels – They typically have a rounder lumen on microscope slides – They have a relatively thick wall compared to their lumen size Veins – carry blood towards the heart – They are lower pressure vessels – They are typically flattened on microscope slides – They have a relatively thin wall compared to their lumen size Capillaries – are the microscopic vessels that are the site of the exchange of gases, nutrients, wastes, etc. between blood and interstitial fluid Fig. 21-2, p. 723 The main types of blood vessels
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2 The structure of blood vessel walls Most BV walls have 3 main layers : –1 . Tunica intima (interna) = a simple squamous endothelium with an underlying basement membrane Internal elastic membrane (found in arteries only) –2 . Tunica media = smooth muscle and CT; it’s thicker in arteries External elastic membrane (found in arteries only) –3 . Tunica externa (adventitia) = a CT sheath that blends into adjacent tissues In arteries: it contains collagen and elastin fibers In veins: it contains collagen, elastin, and smooth muscle; it’s thicker than the tunica media Fig. 21-1, p. 721 Fig. 21-2,
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3 Fig. 21-2, p. 723 •A . Elasticity = the ability to stretch and recoil •B . Contractility : Vasoconstriction = vessel diameter Vasodilation = vessel diameter – It affects peripheral resistance and therefore: • 1. Blood pressure • 2. Afterload on the heart • 3. Blood flow through the capillaries Some general properties of arteries Types of arteries •1 . Elastic arteries a.k.a. conducting arteries – have the largest diameter – They dampen dramatic pressure changes as they conduct a large volume of blood away from the heart •2 . Muscular arteries a.k.a. medium-sized or distribution arteries – They distribute blood to skeletal muscles and internal organs via vasoconstriction and -dilation – Most arteries are this type •3 . Arterioles a.k.a. resistance vessels – have the smallest diameter – They regulate blood flow to capillaries in response to: • A) Local conditions (e.g. CO 2 , O 2 , and/or pH) • B) Sympathetic innervation • C)
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4 Fig. 21-5b, p. 727 Capillaries • Connect arterioles to venules • Have no tunica media or externa – They have an endothelium and underlying basal lamina only • Function : diffusion or active transport of solutes between the blood and interstitial fluid – They have thin walls, low blood velocity, and a large total surface area, all of which exchange Fig. 21-2, p. 723 Types of capillaries Continuous capillaries – have a complete (i.e. continuous ) endothelium – They have openings between endothelial cells only (so they have relatively permeability) – They are found in most regions of the body
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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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Ch21NotesFall10 - Ch. 21 Blood Vessels and Circulation The...

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