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Anatomy Chapter 10.docx

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Biological Sciences
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Ted Petit

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Chapter 10 Blood Vessels and Blood Pressure • Basics - exchanges between blood and tissue cells take place through the interstitial fluid - all organs receive fresh blood 1. amount to each organ adjusted based on need - the blood is constantly "reconditioned" so its composition is relatively constant 1. reconditioning organs receive a high proportion of cardiac output (digestive system, kidneys) - organization "vascular tree" 1. arteries (carries blood from heart toward tissues) 2. arterioles (adjusts blood flow to tissues) 3. capillaries (exchanges made) 4. venules (carries blood to veins) 5. veins (carries blood from tissues toward heart) - flow rate (volume of blood passing through a particular segment of vascular tree per unit time) 1. directly proportional to pressure gradient 2. inversely proportional to resistance (hindrance to flow from friction) a. vessel radius - smaller vessels  more resistance * b. viscosity of blood - thicker blood  more resistance c. length of vessel - longer vessel  more resistance • Arteries - fast transport 1. large - pressure reservoir 1. walls contain endothelial lining surrounded by smooth muscle and connective tissue fibers (collagen and elastin), which allow walls to stretch to contain pumped blood 2. when the heart is relaxing the arteries recoil and keep the blood flowing - arterial pressure fluctuates 1. blood pressure is the force exerted by blood on vessel walls a. depends on blood volume and distensibility of vessel b. systolic pressure is the maximum pressure during systole (should be <120 mmHg) c. diastolic pressure is the pressure during diastole ( should be <80 mmHg) d. systolic - diastolic = pulse pressure (the pressure felt in arteries near the body surface) 2. mean arterial pressure is the main driving force for blood flow to tissues MAP = diastolic pressure + 1/3 pulse pressure • Arterioles - major resistance vessels (small radii) - radii adjusted by smooth muscle 1. vasoconstriction and vasodilation (narrowing and enlarging) 2. normally partially constricted (vascular tone) a. myogenic activity b. sympathetic innervation - local control of arteriolar radius matches blood flow to tissue needs 1. chemical influences a. metabolic factors causing vasodilation (1) decreased O 2 (2) increased CO 2 (3) increased acid (from CO a2d lactic acid) (4) increased K (APs outpacing Na -K pump in brain or skeletal muscle) (5) increased osmolarity (more solutes formed during times of elevated metabolism) (6) release of adenosine (in cardiac muscle) (7) release of prostaglandins (not well understood) b. local metabolic factors probably act by causing release of chemical mediators from endothelial cells (called vasoactive mediators), e.g., (1) endothelial-derived relaxing factor (EDRF), also known as nitric oxide (NO) inhibits Ca2+ influx in smooth muscle - vasodilator (2) endothelin - vasoconstrictor 2. physical influences a. application of heat (vasodilation) or cold (vasoconstriction) b. myogenic responses to stretch (vasoactive substances probably contribute) (1) tone increases in response to increased stretch (resists stretch) - important to keep flow to tissues constant as MAP changes (pressure autoregulation) (2) tone decreases in response to decreased stretch - important in restoring flow to previously deprived tissue (reactive hyperemia) - extrinsic control of arteriolar radius helps regulate arterial BP 1. sympathetic activity produces generalized vasoconstriction, increasing resistance and BP (don't vasoconstrict brain) MAP = CO x total peripheral resistance a. NE at  receptors causes vasoconstriction b. E at  receptors causes vasodilation (heart, skeletal muscles)  2. other hormones a. vasopressin - important in fluid balance, vasoconstrictor b. angiotensin II - important in fluid balance, vasoconstrictor 3. local control mechanisms can override • Capillaries - responsible for exchanges between plasma and interstitial fluid (solute exchange mainly by diffusion) 1. thin-walled, narrow vessels 2. highly branched 3. blood flows slowly through individual vessels 4. lipid soluble substances pass through cells (O , C2 ) 2 5. water soluble substances pass through pores (ions, glucose, amino acids) 6. some vesicular transport (hormones) 7. degree of "leakiness" may change due to actin-myosin in capillary cells - precapillary sphincters 1. rings of smooth muscle can block flow through capillaries in less active tissues a. sensitive to local metabolic changes - fluid shifts and bulk flow 1. impo
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