cardiovascular - lecture 3 Flashcards
HOW DOES flow move
higher pressure to lower pressure
what is blood pressure
force exerted by blood on wall of bv
blood flow = higher to lower pressure
pressure needed for blood flow
what is pressure
force/area
what is systemic bp
120/80mmhg
what is central venous pressure
5-15 cm h2o (6-12mmhg)
when is there no flow
when force = pressurexarea is equal on both sides
no diff in pressur e
when is there flow
p inlet
p outlet
diff pressures =flow
describe flow in capillaries
decrease velocity and pressure = stop from pushing things out through membranes
like at kidneys
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
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
describe diff between systolic and diastolic
pressures higher during systole than diastole
oscillations between the 2 parts of the cardiac cycle
is pressure differences between systole and diastole important in all bv
NOOOO
less significant for arterioles and cap
important for arteries, arterioles and cap
is the oscillation of pressure between the 2 parts of the cycle present all the time
NOO
dissapears in veins and venules
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»_space; Pv (100mmhg vs 5mmhg)
so delta P is around Pa
when is there no flow - perfusion pressure
when delta P = 0
not flowing, static
Pin=Pout
what is flow formula
perfusion pressure/resistance
which vessel regulates flow
arteries
can change diameter
what is hypertension
more resistance so bp increases
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
