cardiovascular - lecture 3 Flashcards by Misha Gandhi

HOW DOES flow move

higher pressure to lower pressure

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what is blood pressure

force exerted by blood on wall of bv
blood flow = higher to lower pressure
pressure needed for blood flow

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what is pressure

force/area

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what is systemic bp

120/80mmhg

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what is central venous pressure

5-15 cm h2o (6-12mmhg)

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when is there no flow

when force = pressurexarea is equal on both sides
no diff in pressur e

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when is there flow

p inlet
p outlet
diff pressures =flow

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describe flow in capillaries

decrease velocity and pressure = stop from pushing things out through membranes
like at kidneys

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describe pressure in blood vessels

increased in arteries and arterioles than in cap, venules and veins
resistance much greater in arteries and arterioles than in cap
arteries and arterioles = high resistance and cap and veins and venules = low resistance
more muscle = contract better, structure is everything

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describe pressure - pulm circ gen

systemic = high
diastolic = low
less significant in smaller vessels, less and less since further away
much easier than whole periphery
pressure lower in pulm circ since small distance

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describe diff between systolic and diastolic

pressures higher during systole than diastole
oscillations between the 2 parts of the cardiac cycle

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is pressure differences between systole and diastole important in all bv

NOOOO
less significant for arterioles and cap
important for arteries, arterioles and cap

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is the oscillation of pressure between the 2 parts of the cycle present all the time

NOO
dissapears in veins and venules

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what is perfusion pressure

perfusion pressure = inlet pressure -outlet pressure
delta P = Pin - Pout
what goes in - what goes out

arterial pressure - venous pressure
but normally Pa&raquo_space; Pv (100mmhg vs 5mmhg)
so delta P is around Pa

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when is there no flow - perfusion pressure

when delta P = 0
not flowing, static
Pin=Pout

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what is flow formula

perfusion pressure/resistance

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which vessel regulates flow

arteries
can change diameter

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what is hypertension

more resistance so bp increases

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what is flow proportional to

perfusion pressure
which is approx equal to arterial pressure

what is resistance

resistance = perfusion pressure/flow
force that opposes movement

what is friction

occurs between vessel wall and blood

what happens when increased vessel length

increases surface= increased resistance

describe friction and vessel lentgh

more resistance and small flow when longer

describe friction and vessel luminal diameter

greatest resistance near surface, slowest flow, more friction
least resistance at center, greatest flow
fluid speed greater in middle of cylinder than at the walls

what is laminar flow

entire fluid flows in same dir opposed to turblent flow (ex = athersclerosis, wont be straight flow v turbulent since plaques)

what depends on viscosity

the flow speed

what is viscosity

friction between moving molecules greater the friction = greater the viscocity = greater resistance to blood flow

what does viscocity depend on in blood

hematocrit more rbcs = more viscous, also if dehydrated

does blood viscosity vary a lot

no since hematocrit varies little blood viscosity generally constance at time should be similar in all blood compartments lenght of bvs also constant in organism

describe poiseuilles law

frictional losses in viscous flow = generation of heat --> fall in pressure down vessel R = 8pivL/A^2 = 8pivL/(pir^2)^2 = 8vL/pir^4 resistance = 8 x viscosity x length/radius valid only for laminar flow

what does viscosity depend on

viscosity and length of vessel usually constant cross sectional area = changes, very important

what can control resistance in vessels

local metabolites (vasoactive peptides) hormones neurotransmitters endothelial cells increase ca = contract, decrease ca = relax

what do endothelial cells do

production of endothelium derived relaxing factors = nitric oxide, protascyclin, edhf (endothelium derived hyperpolarizing factor)

what helps control resistance

contraction

what is R relationship

R inversely proportional to 1/r^4

describe resistance and radius

larger = lower resistance higher vol of blood = must increase pressure and resistance to decrease - arteries

describe vessels or organs in series

vessels in series total resistance of 2 vessels in series = to sum of the resistance of vessels 1 and 2 the total resistance is greater than resistance of individual bvs R=R1+R1

describe vessels or organs in parallel

resistance at entry and exit of system lower than resistance of each in vessels radius of vessel at entrance or exit greater than radius of individual vessel resistance inversely proportional to radius parallel not efficient 1/R = 1/R1 + 1/R2

describe veins and compliance

arteries = more resistance and pressure most of blood found in veins and venules due to high compliance of these bv compared to arteries and arterioles = more resistance

what is compliance

ability of blood vessel to stretch

are veins or arteries more compliant

veins bc little smooth muscle and few elastic layers more vol, dilate better, relaxes well

what does compliance depend on

variations or gradient in vessel vol (delta V) inversely proportional to variation gradient in transmural pressure (delta P)

describe compliance in arteries vs veins

arteries = for a given variation in transmural pressure = the vol changes little veins = vol chnages much more for same variation in transmural pressure venous compliance = more important than arterial compliance

what is compliance formula

1/slope

How is the pressure in the venous system?

bp in peripheral veules <10 percent of that in ascending aorta (largest artery)

name and describe mechanisms needed to maintain flow of blood in veins against gravity

1= valves = system, folds of tunica intima projecting from vessel wall and point in direction of blood flow, ensure one way flow of blood towards heart * can still contract tho, valves ensures proper blood distribution 2 = contraction of skeletal muscles