L10: Overview of Circulation Flashcards
divisions of circulatory system
systemic - arteries and veins
pulmonary - heart and lungs
arterial max and minimum pressure at rest
120/80
capillary pressures ranges
35 to 10
pulmonary systolic and diastolic pressure
25
8
phasic pressure
present in aorta to capillaries due to ventricle pumping
sharpest pressure decrease
present in arterioles due to having the highest resistance
pulse pressure
systolic - diastolic
ex.
120 - 80 = 40
arteries in circulation
transport under high pressure due to close proximity to ventricle contractions
arterioles are control ___
conduits
capillaries are responsible for
exchange between blood and extracellular fluid
veins flow rate
contain valves to prevent back flow
flow rate is dependent upon current state: contract/dilate
controlled by surrounding muscles
blood distribution broad
84% systemic
16% pulmonary
blood distribution to systemic circulation
64% = veins 13% = arteries 7% = capillaries/arterioles
blood flow pattern from heart to lungs
aorta large to small arteries arterioles capillaries venules small to large veins vena cava pulmonary artery lungs arterioles capillaries venules pulmonary vein
velocity of blood flow
V = F/A
A = area F = volume of blood flow
aorta velocity at rest
33 cm/sec
A = 2.5
capillaries velocity at rest
0.3 cm/sec
A = 2500
aorta diameter
2.5
small artery diameter
20 total
arterioles diameter
40 total
capillary diameter
2500 total
venule diameter
250 total
small vein diameter
80 total
vena cava diameter
9
what are the 3 basic principles that underlie circulatory system functions?
- blood flow to each tissue is controlled by the tissue
- the CO is controlled mainly by sum of all the local tissue flows
- artery pressure regulation: independent of local blood flow and CO controls
how is blood flow controlled?
Microvessels monitor tissue needs
blood flow changes as need changes
they act directly on local vessels causing constriction or dilation
what helps the heart get proper CO needs
nerve signals
what can activate if arterial pressure falls?
nervous reflexes
what primarily control cardiac output?
the tissues themselves and their dynamic needs
nervous reflex in response to arterial pressure below 100 mmHg
reflex will cause: increased contractile force constrict large vein reservoirs constrict arterioles kidneys may play role
2 main factors controlling blood flow rates
- pressure gradient
2. resistance
how do we calculate flow thru a vessel
ohm’s law — Poiseuille equation
F = (delta)P/R
flow is directly related to_______ . and inversely related to _____ .
pressure
resistance
Poiseuille’s equation for change in pressure or resistance
(delta)P = F*R
R = (delta)P/F
adult blood flow at rest
5000 mL/min (vessels)
or
5L/min = CO
streamline flow
laminar flow — flow in layers
when does streamline flow occur?
flow is a steady rate
vessel is smooth and long/straight
in streamline flow where will blood travel the fastest?
in the center
or
the farthest distance away from the walls (resistance)
nonlayered flow
turbulent flow
can create murmurs
when does nonlayered flow occur?
flow is too great
obstruction w/in vessel
sharp turn
pass over a rough surface
a greater resistance in flow, causing a tendency for turbulent flow to increase
eddy currents
eddy currents are directly related to?
velocity of flow
diameter of vessel
density of blood
specific gravity of blood
1.055
eddy currents are inversely related to ?
viscosity of blood
blood is 4.5x more viscous than water
measure of the tendency for turbulence to occur
Reynolds number = Re
Re = (vdp)/n n = 1/30 …...so Re = 30vdp
what does the n represent in Re equation?
viscosity
in blood it always = 1/30poise
Re > 200-400
turbulent flow will occur somewhere in vessel
Re > 2000
turbulence will occur in the vessel even if the vessel is straight
we can directly measure resistance
false, we cannot directly measure it
variables used in resistance calculations
- vessel radius**
- blood viscosity
- vessel length
formulas for resistance
R = (delta)P/F
R = 8nl/(pie)r^4
what is the most important variable in resistance?
vessel radius
mean pulmonary arterial pressure
16
mean left atrial pressure
2
total pulmonary vascular resistance = ?
(pulmonary atrial P - left atria P) / CO
(16-2)/100 = 0.14 PRU
PRU
peripheral resistance unit
resistance of entire systemic circulation = ?
total peripheral resistance
how to calculate PRU?
(CO which = 100mL/sec) / (systemic artery P - systemic vein P)
= resistance of entire systemic circulation
R = 4 PRU
vessels are strongly constricted
severe blood loss or heart attack
R = 0.2 PRU
vessels are greatly dilated
define conductance
measure of blood flow through a vessel for a given pressure difference
relate conductance and resistance
conductance is the exact reciprocal of resistance
C = 1/R
conductance equation
Poiseuille’s law
F = (pie)(delta P)r^4 / 8nl
F = flow rate n = viscosity l = length
relate conductance and diameter
conductance is directly proportional to d^4
increase d 4x = flow increase of 256x
how does the relationship between conductance and diameter effect blood vessels?
a minor change in diameter can have a vast impact on flow rate
