Flashcards in Phys test 7 Deck (52):
1
Basic principles of circulatory function
1. Rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need (Flow controlled by tissue need)
2. Cardiac output is controlled by the sum of all the local tissue flows
3. Arterial pressure regulation is generally independent of either local blood flow control or cardiac output control
-foundation of all of the control mechanisms
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First principle
-Q to each tissue is controlled by the tissue need
-most designed to respond to decreases in cardiac output
- local control of arterioles/metarterioles/precapillary sphincsters- BP changes constantly
-Central nervous control and Hormone control- when disaster strikes (not day to day)
-metabolic activity in capillary bed increases= increase Q through that tissue
3
Second principle
-CO controlled by sum of all local tissue flows (venous return)
-if Q through local tissues goes up and venous return goes up= CO goes up
-left and right side of heart, the CO= same
-preload increase= CO increases
-the heart responds immediately to any changes in venous return- automatic response
-CNS not a big role except there is a certain level of Basal level of sympathetic and parasympathetic tone (only when things get out of wack)
4
Starling's Law of the heart
-the heart responds immediately to any changes in venous return- automatic response
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Third principle
-arterial pressure regulation is generally independent of either local Q to local tissues or CO control
-BP independent of Q and CO
-important because the capillaries are a parallel circuit so therefore the pressure going in and out is equal
-BP regulation is closely regulated by variety of sensor feedback systems and kidneys
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If pressure fall quickly, feedback systems will
-increase in cardiac contractility (increase symp tone) (quick change)
-constrict large veins which transfers volume to arteries (quick change)= venous return goes up=CO goes up
-stimulate generalized constriction of arterioles holding more volume in arteries (increase resistance=volume of blood in arteries=BP increases)(quick change)
-stimulate renal controlled change in overall circulating blood volume (slow change)
-controlled by ANS
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Hemodynamic principals
-ohm's law- relationship between blood flow, pressure drop across the system, and resistance to flow through the system (dP=QxR)
-reynolds' number- measure of the tendency for turbulence to occur
-poiseuille's law- factors that affect resistance to flow though the system.
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flow through vessels in series
P=QR
-Q same through all vessels in series
-pressure drop across each segment depends on resistance of each segment
-velocity of flow will vary inversely with diameter of the vessel- the smaller the diameter the higher velocity
-when velocity drops (such as through the filters), it makes it easier for the air bubbles to leave the blood stream and into purge
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flow through vessels in parallel
P=QR
-relationship between total resistance and resistance of each individual tissue=total resistance is always smaller than the smallest resistance within the tissues
-pressure coming in and out must be the same for each vessel
-Total flow through all vessels = flow into the network and flow out of the network
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Laminar flow
-silent flow
-center of flow fastest, no flow at boundary layer
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Turbulent flow caused by
-high velocity of blood
-narrowing of blood vessel or valve
-mitral stenosis= turbulent flow which causes a murmur sound
-aortic insufficiency= causes a different sounding murmur because of blood flow coming back in
-generates sound Cardiac murmurs
-might be able to feel (bruits) in peripheral blood vessels
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Shear Stress (SS)
-force exerted on vessel wall by the moving blood
-force wants to drag the vessels wall along with the blood because the center of the vessel is moving much quicker than the outside and it wants to drag the slower layer with it
-increases resistance to flow and increases hemolysis
-SS = 4(viscosity)Q /(pi)r^3
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Reynolds' number
-measure of tendency for turbulence to occur
-Re = ((velocity)(diameter)(Density)) / (viscosity)
-relationship between forces holding fluid together versus forces trying to pull fluid apart
- ((velocity)(diameter)(Density))= forces pulling fluid apart
-(viscosity)= forces pushing fluid together
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Turbulence based on branches
-Side branches turbulence occurs much easier and at a lower Reynolds' number (R=200-400)
-Straight tube turbulence occurs much higher Reynold's number (Re= 2000)
-Aorta, when vent ejects you will have turbulence (worse when arterial cannula)
-very seldom in smaller arteries
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Poiseuille's Law
-Q = ((Pi)(ΔP)(r^4)) / ((8)(viscosity)(Length))
-P and Q are same as Ohm's law and everything else is the R of the law
-diameter has the largest effect
-the larger the diameter, the easier flow and less resistance
-local tissue flow is going to be controlled within the local tissues themselves by changing the diameter of the blood vessels (precapillary sphincters and metarterials)
-SMALL CHANGES PRODUCE BIG CHANGES IN FLOW
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what changes viscosity of the blood
-temperature goes down and viscosity goes up
-plasma protein concentration goes down so viscosity goes down
-red blood cell concentration (HCT) goes up so viscosity goes up
-relationship between flow and sheer stress
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effects of changing hematocrit of viscosity
-viscosity of plasma= 1.5
-at a normal HCT (40), blood is 3 times more viscous than water (viscosity of 4) and normal body temperature
-plasma protein held constant because viscosity of plasma would have changed
-cool patient= viscosity goes up
-dilute patient= viscosity goes down
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effect of flow and shear stress on viscosity
-viscosity is proportional to shear stress
-viscosity inversely proportional to flow
-viscosity increases as sheer stress increases or flow decreases
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effect on flow and shear stress on viscosity as a problem
-flow decreases in capillaries because many parallel circuits so flow and diameter will be very small so an increase in viscosity to flow because the resistance is high
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capillary sludging
-High resistance in capillary bed because of viscosity so high that the blood becomes less fluid and plug up the capillary so there is no flow= no oxygen able to be sent to that area
-normal in deep hypothermia but metabolic activity is low so won't need to provide as much
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dilute plasma proteins, what happens to viscosity
decreases
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dilute RBC, what happens to viscosity
decreases
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cool the patient, what happens to viscosity
increases
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give a vasoconstrictor, what happens
-decrease diameter of arterioles
-potential to decrease flow through capillaries
-potentially increase viscosity
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systemic circulation
-peripheral circulation
-maintains constant internal environment (interstitial fluid)
-every cell gets what it need and removes what it needs
-everything happens at the capillaries
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pulmonary circulation
-gas exchange at capillaries
-bring blood flow into contact with the respiratory membrane of the lungs for gas exchange
27
arteries
-elastic not muscular
-little to no smooth muscle
-strong walls
-transport at high pressures and high velocities
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arterioles
-last and smallest branches of arteries
-control flow through each capillary bed
-strong walls
-very muscular
-control blood flow through each capillary bed
-controlled by ANS
-can constrict completely closed and dilate to large radius
-if patient goes into shock, two organs get blood flow (brain and heart) because the arterioles shut off blood flow everywhere else
-normal constrictive state is halfway constricted
-decrease in symp tone causes dilation and increase in symp tone causes constriction
29
capillaries
-all exchange here
-very thin with gaps between cells
-very permeable to water and small molecules
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endothelial cells
-line heart and valves
-line entire cardiovascular system
-active tissue
31
endothelial cells as active tissue
-produce variety of active substances
-aid and inhibit coagulation at the same time with the anticoagulation factor winning so we don't clot
-affect function of platelets and neutrophils
-major role in reperfusion injury because we damage these cells and they begin to produce substances we don't want to be produced
-can interact with inactive plasma proteins resulting in activation (clotting cascade)
32
capillary pathways for solute movement
-very small gaps
-water soluble
-permeable to lipid-soluble substances
-too small for proteins to leave
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transcapillary fluid movement
-Pc- capillary hydrostatic pressure (20-25 mmHg)- push things out of the cell
-Pi- interstitial pressure (-3)- pull things out of capillary
-capillary oncotic pressure (28)- pulling fluid in
-intersticial oncotic pressure (8)- pull fluid out
-filtration is net movement out of the capillary (arterial end)
-reabsorption is net movement into capillary (venous end)
-net filtration (movement of fluid out)
34
Lymphatic system
-provides pathway for excess interstitial fluid and large molecules such as proteins to return to circulatory system
-all paths lead to lymph nodes (pull bacteria and other foreign objects out of interstitial fluid
-same size as capillaries but larger pores
-fluid channeled with one-way valves
-returns to circulatory system by the right side of the heart
-about 2.5 L of lymphatic flow is returned to circulatory system each day
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Veins
-transport at low pressures
-capacitance vessels
-thin walls
-very compliant- big change in volume and a small change in pressure
-velocity higher than capillaries but lower than arteries
-controllable blood reservoir so that it can shift quickly between veins and arteries
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Peripheral veins
-veins outside of thorax
37
central veins
-major veins within the thorax
-lowest pressure in vascular system
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Aorta internal diameter
2.5 cm
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aorta wall thickness
2 mm
40
total cross sectional area of aorta
4.5 cm2
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arterioles internal diameter
30 micrometers
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arterioles wall thickness
1 micrometer
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arterioles number
5x10^7
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total cross sectional area of arterioles
20 cm^2
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capillaries internal diameter
5 micrometers
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capillaries wall thickness
1 micrometer
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capillaries number
10^10
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total cross sectional area of capillaries
4500 cm^2
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vena cava internal diameter
3 cm
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vena cava wall thickness
1.5 mm
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total cross sectional area of vena cava
18 cm^2
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