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45 Cards in this Set
- Front
- Back
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Mean Arterial Pressure (MAP)
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of the aorta is approximately 85mmHg.
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Central Venous Pressure (CVP)
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of the large veins emptying into the R. Atrium isabout 2-8mmHg. Since the CVP is sosmall, it is usually ignored and the ΔP is 85mmHg.
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Resistance– determined by 3 factors:
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Vessel radius
Vessel length Blood viscosity |
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Vessel radius
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as radius decreases (vasoconstriction), resistance increases and as radius increases (vasodilation) the resistance decreases
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Vessel length
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as the vessel length increases, resistanceincreases (and vice versa.
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Blood viscosity
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as viscosity (thickness) increases, resistanceincreases
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What is the flow of the blood vessels |
BloodVessels = Vasculature: heart - arterioles - capillaries - venules - veins - heart
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Arteries
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conduct blood away from the heart
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Large Arteries
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In large arteries, the wall contains smooth muscle and lots of elastinfibers. The large arteries actas pressure reservoirs(storage sites for pressure to ensure continual, smooth flow ofblood).
a.Asthe arterial walls are expanding due to increased volume duringsystole, the elastin fibers are like a spring being stretched. b.Theelastic force is stored such thatduring diastole, when no moreblood is entering the arteries, the walls passively recoil inward, propelling blood forward. |
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Arterioles
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we go from large arteries to arterioles
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What happens once the large arteries go to arterioles |
(1) the amount of elastinfibers decrease;
(2) the smooth muscle of the wall becomes thepredominant feature; and (3) the pressure drops. |
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What happens to the arterioles |
The arterioles provide the greatest resistance to blood flow (~60%)– 2 reasons: i. thevessel radius decreases ii. vasoconstriction and vasodilation(contract or relaxmuscle)
* This resistance determines (1) amount ofblood flow to capillaries and (2) blood pressure. |
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The vasoconstriction and vasodilation iscontrolled by |
Intrinsic and extrinsic control mechanisms
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Intrinsic control mechanisms
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these are controls occurring in the organitself. 4 examples:
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What are the 4 examples of Intrinsic control mechanism |
Active Hyperemia Reactive Hyperemia Myogenic Response Chemical Messengers |
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Active Hyperemia
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a vasodilation or vasoconstriction based onmetabolic activity
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Reactive Hyperemia
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a vasodilation based on a decrease in blood flow.
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Myogenic Response
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arteriole smooth muscle contains stretch-sensitivefibers. Thus, as the MAP increases, the arteriolar wall isstretched. The response is vasoconstrictionand vice versa!
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Chemical Messengers
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the cells lining the blood vessel (in theendothelium) can release chemicals, which relax or contract arteriolar muscle:Exs
-nitricoxide = vasodilator -endothelin-1= vasoconstrictor |
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There are 3 types of Extrinsic Control Mechanisms, what are they |
Sympathetic Nervous System Vasopressin Angiotensin II |
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Sympathetic Nervous System
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under stress the neurons of this system areactivated.norepinephrine is released, which binds to the alpha adrenergicreceptors on the smooth muscle cells causing vasoconstriction,increased R, and increased MAP.
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Where is Epinephrine released from |
adrenal gland |
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what binds to epinephrine |
Like norepinephrine it will bind to the alphaadrenergic receptors and cause vasoconstriction
It can also bind to beta 2 adrenergicreceptors. At low levels it has ahigher affinity for beta 2 adrenergic receptors (= vasodilation), butat high levels it can bind to either. Since most arteriolar muscle contains alphas the effect is primarily vasoconstriction,but in the arteriolar muscle of heart and skeletal muscle, betas predominate = vasodilation. |
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Vasopressin
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(AntidiureticHormone, ADH) – increases MAP; vasoconstricts,
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Angiotensin II
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increases MAP; vasoconstricts
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Capillaries
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smallest blood vessels (10-40 billion in thebody); exchanges between the blood and the tissue cells occur through theirthin walls by diffusion
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What are the two types of capillaries |
Continuous Fenestrated |
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Continuous (Capillaries) |
most common,they have small gaps between the cells which allows for permeability of smallsized molecules and/or lipid soluble molecules (oxygen, carbon dioxide, steroidhormones, etc.). Permeability of largemolecules (proteins) is low.
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Fenestrated |
the cells havepores (= fenestrations). The pores allow for rapid movement of water-soluble molecules (sodium,potassium, glucose, etc), large proteins and even cells. Found in organs (kidneys, liver, and bonemarrow) which depend on rapid movement of materials.
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how is the flow into capillary beds (networks) |
regulated by themetarterioles and precapillary sphincters.
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how does the bulk flow across capillary wall |
from blood tointerstitial fluid = filtration; from interstitialfluid to blood = absorption. The forces driving the movement into andout of the capillaries = Starling’sforces (4 of them).
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What are the 4 Starling forces |
1. Capillary hydrostatic pressure 2. Interstitial fluid pressure 3. Capillary osmotic pressure 4. Interstitial fluid osmotic pressure |
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Capillary hydrostatic pressure
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the pressureexerted by the fluid in the capillary = blood pressure. This favors filtration. This pressure decreases as you move down thecapillary (from arteriolar end to venule end).
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Interstitial fluid pressure
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this forceopposes Capillary hydrostatic pressure At the venule end, when CHP. decreases, the interstitial fluid pressure is greater and absorptionis favored.
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capillary osmotic pressure
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NOTE: thepresence of a nonpermeating solute exerts an osmotic pressure that tends todraw water to the side where it is present in greater concentration. The most prevalent of these solutes in theblood are large proteins. These generatethe capillary osmotic pressure. Thisfavors absorption.
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interstitial fluid osmotic pressure
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interstitial fluid osmotic pressure
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Net Filtration Pressure (NFP)
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filtration pressure– absorption pressure NFP= (Capillary hydrostatic pressure + interstitial fluid osmotic pressure) – (interstitial fluid pressure + capillary osmotic pressure)
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Arteriolar end
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NFP = (38 + 0) – (25 + 1) NFP = 12mm Hg (filtration)
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· Venuleend:
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NFP = (16 + 0) – (25 + 1)NFP = - 10mm Hg (absorption)
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Venules
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vessels slightlylarger than the capillaries. They fusetogether to form veins.
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Veins
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these have thinwalls compared to arteries (considerably less pressure here) and have muchlarger lumens. The larger veins have one-way valves. They are high compliance vessels (thatis, a relatively small increase in the pressure within veins causes a relativelylarge degree of expansion [increase in volume]). Thus, at any givenpressure, veins can hold more blood than arteries = volume reservoir. At anygiven time ~ 60% of the blood is in the veins. 4 factors affect the flow of blood through the veins:
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skeletal muscle pump
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when musclescontract venous pressure increases and return increases
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respiratory pump
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when we take abreath the chest pressure drops (no valves in chest veins), the diaphragmflattens, and abdominal pressure increases (abdominal veins have valves); bloodis pushed upward into chest.
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blood volume
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as blood volumedecreases, venous pressure falls, venous return to heart falls, end-systolicvolume drops, cardiac output falls and thus MAP drops and vice versa.
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vasomotor tone
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when thesympathetic nervous sys. is activated, the veins constrict, venous pressurerises, venous return increases, CO increases, and MAP increases.
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