Hemodynamics, Systemic Circulation Flashcards
structure of aorta
lots of elastic fiber
largest wall thickness
precapillary sphincter vs arteriole?
sphincter has a thicker wall
composition of capillary?
just endothelial cells
venules are also only endothelial cells**
arteries
thick elastic walls
serve as pressure reservoir
veins
serve as blood reservoir
arterioles
resistance vessels
can contract smooth vessels to increase resistance
capillaries
site of exchange
where is most of blood volume
systemic greater than pulmonary
veins
volume reservoir
2nd reserve is pulmonary circulation
immediate blood loss?
veins are a reservoir
most of volume where?
systemic veins
where is blood pressure highest?
at the aorta
where is greatest pressure drop?
at the level of the arterioles
resistance vessels
arteries and BP?
maintain the MAP
mean arterial pressure
driving force for blood flow
pressure gradient
must be maintained to ensure adequate blood supply
auscultatory BP?
SBP
DBP
palpatory BP?
SBP
systolic pressure
higher
diastolic pressure
lower
korotkoff sounds
turbulent flow that is heard when measuring a blood pressure
how to approximate mean pressure in arteries?
time spent in diastole is greater**
MAP = DBP + 1/3 PP
PP is difference between systolic and diastolic
MAP = DBP + 1/3 (SBP - DBP)
what happens during exercise with mean pressure?
spend less time in diastole than at rest
MAP = DBP + 1/2 (SBP - DBP)
where is blood pressure when standing the highest?
dorsalis pedis
effect of gravity on blood pressure?
when standing
- hydrostatic pressure increases
- you have a fluid column
much greater pressure at level of the feet
decreased pressure as you go above the heart
- *this is important when going from supine to standing and the pooling in the veins due to the greater pressure
- you become light headed
cross sectional area?
greatest at the capillaries
velocity of flow?
slowest at capillaries
aorta CSA?
greatest diameter, smallest CSA
blood flow rate?
L/min
volume of blood per unit time
equal for ALL segments
fick principle
indirect method to determine blood flow
based on total O2 consumption and difference between arterial and venous O2 content
fick principle equation?
CO = oxygen consumption / arterial - venous O2
Q = VO2 / A - V O2 difference
blood flow velocity?
mm/sec
highest in aorta
lowest in capillaries
flow velocity?
flow velocity = flow / cross sectional area
laminar flow
silent
turbulent flow
produces murmurs
reynolds number?
threshold from where you transition from silent flow to turbulent flow
what can cause increased turbulent flow?
- *increase in velocity of blood flow
- local decrease in diameter
increased diameter
decreased viscosity
which vessel would likely first develop turbulent flow in an anemic patient?
????
C?
C = deltaV / deltaP
compliance?
given change in pressure, what is the change in volume
systemic veins?
20x more compliant
serve as major blood reservoir
effect of aging on pulse pressure
compliance of vessels decreased
and an increase in pulse pressure
compliant artery?
smaller pulse pressure vs a stiffer artery
LaPlace’s Law
wall stress
-effect of pressure, radius, wall thickness
T ~ P x r / 2h
LaPlace and BP?
2x radius has to withstand 2x wall tension
greatest wall tension?
aorta
arteries and wall tension?
fibrous bands reinforce to protect against aneurysm
damage or reduction of elastic fibers?
vessels enlarge - aneurysm
driving force for blood flow?
pressure gradient
flow = ?
Flow = pressure gradient / resistance
CO = ?
MAP / TPR
TPR - total peripheral resistance
CO = Q = cardiac output = flow
Ohm’s Law =?
I = V/R
flow regulation?
by resistance
not enough blood to supply entire body
alter the resistance
in series?
flow is equal at all points
adding resistance always increases overall resistance
total resistance always greater than any one individual
in parallel?
flow can be independently regulated
adding resistance in parallel decreases overall resistance
total resistance always less than any one individual
what does parallel allow?
allows for regulation of flow distribution while maintaining MAP
obesity - adds in parallel, decreasing TPR, necessitating increased CO to maintain MAP
where is adequate flow always required?
brain and heart
flow?
inversely proportional to resistance
Poiseuille’s law
radius is key determinant to resistance
increased radius
decrease resistance
increase flow
blood flow is proportional to what?
directly to radius to 4th power
directly to pressure gradient
inversely to vessel length and blood viscosity
anemia?
decreases viscosity, increases flow
polycythemia?
increases viscosity, decreases flow
two ways to control resistance to flow?
extrinsic - neural, endocrine
intrinsic -
biggest influence on resistance?
sympathetic influence
vasoconstriction?
alpha-1 receptors
vasodilation?
beta-2 receptors
endocrine/paracrine influence?
influence vascular tone
key for extrinsic regulation of TPR?
total peripheral resistance
sympathetic nervous system
- alpha 1 receptors
- norepinephrine or epinephrine
promotes vasoconstriction
example of extrinsic control
orthostatic hypertension
intrinsic control?
matching blood flow to tissues need
mediated by local factors on arteriolar smooth muscle
autoregulation
flow independent of blood pressure
flow proportional to tissue metabolism
flow independent of nervous reflexes
cerebral, coronary, skeletal muscle, renal tissues
