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102 Cards in this Set
- Front
- Back
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what is the stressed volume?
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the blood volume contained in the arteries
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what is the site of highest resistance of the cardiovascular system?
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arterioles
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what ANS receptors are found in the arterioles of the skin, splanchnic and renal circulations?
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alpha-1 adrenergic receptors
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what ANS receptors are found in the arterioles of skeletal muscle?
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Beta-2 adrenergic receptors
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Which vessels have the lowest vascular resistance? Why?
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capillaries, due to their parallel arrangement (highest cross-sectional area).
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Describe the histology of large arteries
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thick-walled, with extensive elastic tissue and smooth muscle
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describe the histology of arterioles
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smooth muscle wall that is highly innervated by ANS
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describe teh histology of capillaries
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consist of a single layer of endothelial cells surrounded by basal lamina. thin-walled
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where is the majority of the blood stored in the body?
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veins
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what is the unstressed volume?
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the blood volume contained in the veins
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what ANS receptors are present in veins?
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alpha-1 adrenergic receptors
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What is the formula for calculating Cardiac Output?
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Cardiac Output = (mean arterial pressure - right atrial pressure) / Total peripheral resistance
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what happens to the total resistance if an artery is added in parallel?
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resistance decreases. (you increase the surface area through which the blood can flow)
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if the radius of an artery is doubled what happens to the resistance to flow through that artery?
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resistance is decreased by a factor of 16
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what factor causes the reynold's number of blood to increase?
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decreased viscosity (low hematocrit, anemia) and increased blood velocity (narrowing of a vessel)
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what is the result of a high reynold's number in the blood?
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greater tendency for turbulence, causes audible bruits. Turbulent flow may result in clot formation.
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what is capacitance?
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ability of a blood vessel to distend. inversely related to elastance
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which has greater capacitance, arteries or veins?
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veins
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where in the vascular system would one find the greatest decrease in pressure? why?
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across the arterioles due to it being the greatest site of resistance
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what is the mean arterial pressure of the aorta?
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100 mmHg
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what is the mean arterial pressure of the arterioles?
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50 mmHg
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what is the mean arterial pressure of the capillaries?
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20 mmHg
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what is the mean pressure of the Vena Cava?
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4 mmHg
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what is the pulse pressure?
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the difference between the systolic and diastolic pressures
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what is the most important determinant of pulse pressure?
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stroke volume
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how does one measure the left atrial pressure?
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pulmonary wedge pressure
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how does one calculate the mean arterial pressure?
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diastolic pressure plus 1/3 pulse pressure
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What is the PR interval and what is its significance?
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It is the interval between the beginning of the P wave to the beginning of the Q wave. It is a measure of the conduction velocity through the AV node
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what does an increased PR interval signify?
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AV nodal heart block
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What is the QT interval and what is its significance?
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QT interval is measured from the beginning of the Q wave to the end of the T wave. It represents the entire period of depolarization and repolarization of the ventricles
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What is the ST segment?
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the segment from the end of the S wave to the beginning of the T wave; it is isoelectric period of ventricular depolarization
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What determines the resting membrane potential?
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conductance to K+
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what is resting membrane potential of myocardial cells?
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-90 mV
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Describe Phase 0 of the cardiac action potential?
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upstroke of action potential; It is marked by a transient increase in Na conductance that has inward flow of ions depolarizing membrane
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Describe Phase 1 of the cardiac action potential
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initial repolarization caused by outward flow of K ions
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Describe Phase 2 of the cardiac action potential
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plateau of AP; transient increase in Ca conductance that results in an inward flow of Ca along with a balanced outward flow of K
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Describe Phase 3 of the cardiac AP
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Repolarization; Ca conductance decreases, K conductance increases; large outward flow of K toward Vm(K), hyperpolarizing the membrane
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Describe Phase 4 of the cardiac AP
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resting membrane potential; inward adn outward currents are equal and Vm approaches K equilibrium potential
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Where is the pacemaker of the heart?
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SA node
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How is Phase 4 of the SA nodal AP different from the other cardiac APs?
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It undergoes phase 4 depolarization. Phase 4 is unstable and derives automaticity from slow inward Na current depolarizing the cell
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How is Phase 0 or the SA nodal AP different from the other cardiac APs?
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Membrane depolarization is due to influx of Ca in SA node, where the atrial, ventricular and purkinje APs are a result of Na currents
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How are phases 1 and 2 different in the SA nodal AP different from the other cardiac APs
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Phases 1 and 2 do not exist in the SA nodal AP
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What determines the speed of the conduction velocity?
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size of inward current during phase 0 of the AP
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Where is the conductance velocity fastest? Slowest?
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Fastest in the purkinje system and slowest in the AV node (to allow time for ventricular filling)
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What are chronotropic effects?
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changes in heart rate
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How are chronotropic effects elicited?
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by affecting the firing rate of the SA node
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What are Dromotropic effects?
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changes in conduction velocity, primarily in AV node.
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How do dromotropic changes affect ECG readings?
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negative dromotropic effects, slow AV conduction and increase PR interval; positive dromotropic effects are the opposite.
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Which parts of the heart have parasympathetic vagal innervation?
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SA node, atria, AV node.
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What receptors does ACh affect in the heart and what are the effects?
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Muscarinic receptors; causes decrease in HR, decreased conduction velocity through AV node, decreases contractility of atria
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what is the mechanism of decreased dromotropic effect?
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decreased inward Ca current and increased relative outward K current causing longer APs
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These receptors cause constriction of skin, splanchnic, and skeletal vascular smooth muscle
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alpha-1 adrenergic receptors
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these receptors cause relaxation of skeletal muscle
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Beta-2 adrenergic receptors
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What is the mechanism of the positive chronotropic effect?
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increased inward Na current during phase 4 depolarization in SA node
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how do cardiac muscles communicate?
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through gap junctions
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where is Ca stored for excitation-contraction coupling?
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in the Sarcoplasmic Reticulum
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how does an influx of Ca cause muscle contraction?
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Ca binds to troponin C, causing tropomyosin to cease the inhibition of actin and myosin binding.
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How does one estimate cardiac contractility?
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Ejection Fraction (stroke volume / end-diastolic volume)
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What is the normal EF?
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0.55
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What are three factors that increase contractility?
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increased heart rate, sympathetic stimulation (catecholamines) via Beta-1 receptors, and cardiac glycosides (digitalis)
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By what mechanism does digitalis increase the force of contraction?
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inhibiting Na,K-ATPase in the myocardial cell membrane
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What factors decrease contractility?
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parasympathetic ACh stimulation in the atria
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What is preload?
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it is equivalent to end-diastolic volume, which is related to right atrial pressure
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What is afterload?
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determined in the LV by aortic pressure, and in the RV by pulmonary artery pressure
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What is the Frank-Starling relationship?
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an increase in preload results in stretching of the sarcomere, and a resulting increase in developed tension (and increase in SV).
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what is the mechanism that matches cardiac output to venous return?
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Frank-Starling relationship
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What phase of the pressure-volume ventricular diagram is altered by an increase in preload?
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end-diastolic volume is increased, so the isovolumetric contraction phase is shifted to the right and increases stroke volume
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What phase of the pressure-volume ventricular diagram is altered by an increase in afterload?
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an increase in aortic pressure will create more resistance to LV contraction. The end-systolic volume will shift right (increase), causing a decrease in stroke volume
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What phase of the pressure-volume ventricular diagram is altered by an increase in contractility?
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this results in an increase in LV pressure during systole, reducing the end-systolic LV volume and increasing stroke volume
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What factors increase Mean systemic pressure?
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increase in blood volume or decrease in venous compliance
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an increase in blood volume has what effect on cardiac output and right atrial pressure?
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both are increased
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What effect does an increase in TPR have on CO, venous return, and right arterial pressure?
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CO and venous return are decreased but RA pressure is unchanged
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how is the stroke volume calculated?
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end-diastolic volume - end-systolic volume
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calculation for cardiac output?
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CO = stroke volume x heart rate
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what is the primary energy source for cardiac stroke work?
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fatty acids
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Cardiac oxygen consumption is increased by what?
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afterload, size of heart, contractility, heart rate
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what is the cardiac output in terms of O2 consumption?
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CO = O2 consumption / (PaO2 - PvO2)
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during what phase of the cardiac cycle do you hear the first heart sound? what causes the sound?
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heard during isovolumetric contraction. caused by closure of the mitral and tricuspid valves
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during what phase of the cardiac cycle do you hear the second heart sound? what causes the sound?
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heard during isovolumetric relaxation. caused by closure of the aortic and pulmonic valves
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what and where are baroreceptors?
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stretch receptors found within the walls of the carotid sinus
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What happens to the baroreceptors when there is a decrease in arterial pressure?
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reduced stretch in baroreceptors --> reduced firing of APs in baroreceptors --> decreased sympathetic outflow to heart and blood vessels by vasomotor center
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what are the end effects of an attempt to increase arterial pressure from baroreceptor activation?
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increased heart rate, increased contractility and stroke volume, increased vasoconstriction of arterioles, increased vasoconstriction of veins
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What causes the release of Renin?
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decrease in renal perfusion pressure causes juxtaglomerular cells of the afferent arteriole to secrete renin
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What is the function of renin?
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converts angiotensinogen to angiotensin I
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What are the effects of angiotensin II?
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stimulates secretion of aldosterone by adrenal cortex (increases Na reabsorption in by renal distal tubule) and causes vasoconstriction of efferent arterioles, increasing TPR and MAP
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What is the cushing reaction?
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increases in intracranial pressure cause compression of cerebral blood flow --> cerebral ischemia --> increase in sympathetic outflow to heart and blood vessels to correct for cerebral ischemia --> profound increase in arterial pressure
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ADH acts on which receptors to cause vasoconstriction?
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V1 receptors
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ADH acts on what receptors in the renal distal tubule and collecting ducts to increase water reabsorption?
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V2 receptors
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What is the function of ANP?
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released from RA due to increased atrial pressure --> causes relaxation of vascular smooth muscle, decreasing TPR --> also causes increased excretion of Na and water by kidney to reduce blood volume --> inhibits renin secretion
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What factors increase filtration out of the capillary?
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increased capillary hydrostatic pressure and interstitial osmotic pressure and decreased interstitial hydrostatic pressure and capillary osmotic pressure
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what is the mechanism and function of NO?
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causes relaxation of smooth muscle by stimulating guanylate cyclase, which produces cGMP.
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what products of metabolic activity will cause a local increase in perfusion?
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CO2, H, K, lactate, adenosine
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histamine does what to blood vessels?
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arteriolar dilation and venous constriction, resulting in increased capillary hydrostatic pressure and increased filtration
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bradykinin does what to blood vessels?
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arteriolar dilation and venous constriction, resulting in increased capillary hydrostatic pressure and increased filtration
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By what mechanism does edema occur?
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filtration through capillary beds exceeds lymph drainage capacity.
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serotonin does what to blood vessels?
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it causes arteriolar constriction and is releasedin response to blood vessel damage to help prevent blood loss. it has been implicated in vascular spasms of migraine headaches
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which prostaglandins cause vasoconstriction?
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F-series prostaglandins and Thromboxane A2
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which prostaglandins cause vasodilation?
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DIE-AE prostaglandin D, I, E1 and E2 and A2
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what are the most important local metabolic factors in the coronary circulation?
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hypoxia and adenosine
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what controls the cerebral circulation?
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metabolic factors almost exclusively
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what factor causes cerebral artery vasodilation?
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CO2
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what are the effects on the CV system during exercise?
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increased sympathetic outflow; increased CO; increased venous return; arteriolar resistance in skin, splanchnic regions, kidneys and inactive muscles is increased
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