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8 Cards in this Set
- Front
- Back
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The Arterial System
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Primary function
to distribute blood to the capillary bed throughout the body the arterioles are the terminal components of the arterial system & serve to regulate the distribution of flow to the various capillary beds Primary regulated variable (MAP) Constitutes a considerable blood volume & distensibility hydraulic filter converts pulsatile output of heart to steady flow through capillaries |
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MAP
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Pressure in large arteries averaged over time
primarily depends on arterial blood volume & arterial compliance SBP & DBP are upper & lower limits of periodic oscillations about MAP PP= SBP-DBP PP determined by SV & arterial compliance transmural pressure= Pin-Pout Primary regluated variable of CV system MAP= CO x TPR DBP + 1/3(SBP-DBP) DBP + 1/3PP MAP falls when CO, TPR, or both fall (vice versa) Correcting a change in MAP requires appropriate change in CO &/or TPR however only peripheral vasoconstriction will restore MAP when ability to increase CVP & CO is limited (upright posture, heat stress) |
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Components of Blood Vessel Pressure
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Static pressure: related to volume of blood within the vascular system at 0 flow (no CO; cardiac arrest; mean circulatory filling pressure 7 mmHg)
Hydrostatic pressure: due to force of gravity Dynamic pressure: generated by the heart All 3 pressures contribute to pressure within the blood vessel |
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Determinants of MAP: CO
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Sudden changes in CO do not result in immediate changes in VR
delayed compliance of the blood vessels compliance will determine rate not magnitude of increase in MAP MAP will increase to a level such that CO=VR Increased MAP due to arterial distention increased arterial volume |
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Determinants of MAP: SV
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Assume compliance is constant
Increase in SV (assuming constant HR & TPR) would increase MAP greater effect on SBP than DBP |
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Determinants of MAP: TPR
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Assuming constant CO
abrupt increases in R decrease VR increase pressure drop increase resistance to flow Under steady state conditions CO=VR increased MAP passive redistribution of blood volume |
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Baroreflex Control of MAP
Decrease MAP |
A resistance raising reflex
Increase in vascular resistance by slow sympathetically mediated vasoconstriction Increase in HR, SV & CO have limited efficacy |
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Baroreflex Control of MAP
Increase MAP |
Correction is rapid via vagal activation of heart
Decrease HR, SV & CO Decrease in Vascular resistance is minor little resting sympathetic tone to withdrawal in humans PSNS does not cause vasodilation most in humans is due to passive withdrawal of SNA except in human skin |
