B4.064 Prework 2: Regional Circulations Flashcards
flow =
pressure gradient / resistance in organ
when vasoconstrictor nerves are cute and arterioles are maximally vasodilated, how does flow increase in the skeletal muscle
over 20 fold
when vasoconstrictor nerves are cute and arterioles are maximally vasodilated, how does flow increase in the heart
5 fold
when vasoconstrictor nerves are cute and arterioles are maximally vasodilated, how does flow increase in the brain and liver
2 to 3 fold
when vasoconstrictor nerves are cute and arterioles are maximally vasodilated, how does flow increase in the kidneys
only 16%
high resting blood flow
what is the pressure gradient driving blood flow to systemic organs
MAP-RAP
does the pressure gradient differ between systemic organs?
no, all the same
what determines the variance in resting blood flow to organs?
differences in vascular resistances between organs
what is the primary determinant of organ vascular resistance
changes in metabolic needs, primarily changes in tissue O2 levels
which organ systems have the most sophisticated mechanisms for local control of blood flow
heart and brain
O2 uptake in an organ =
blood flow * (a-v)O2
what is (a-v)O2
O2 extraction
what determines ability of an organ to extract O2
total surface area of perfused capillaries
fick equation
CO = O2 consumption/ (a-v)O2
how much O2 does the heart extract from oxygen?
as much as 75% even at rest
systemic organs only 25% at rest
coronary sinus blood content = 5 ml O2
what controls O2 uptake in heart
all capillaries perfused at rest, SA cannot be increased
increased O2 uptake is dependent on changes in blood flow only
what controls O2 uptake in kidneys
increase capillary surface area by opening pre capillary sphincters
renal blood flow cant increase very much (max 16%)
what is autoregulation
the ability of an organ to maintain blood flow relatively constant in response to changes in systemic arterial pressure
occurs over arterial pressures from 70-180 mmHg
which organs exhibit autoregulation
brain and heart
how is flow maintained in the heart and brain
at low MAP, arteriolar dilation
at high MAP, arteriolar constriction
limited by maximal dilation or maximal constriction of arterioles
what happens in systemic arterioles with changes in arterial pressure?
at low MAP, arteriolar constriction due to increased SYM firing via baroreflex
at high MAP, arteriolar dilation due to decreased SYM firing via baroreflex
what is the myogenic response?
change in arteriolar diameter after a sudden increase in intravascular pressure
high pressure > increased stretch of vessel wall > increased frequency of action potentials in vascular SM > Ca2+ channels open > Ca2+ influx > constriction
what is the purpose of the myogenic response?
increases resistance in an arteriole to minimize an increase in flow while pressure is high
what determines interstitial concentration of vasodilator metabolites?
rate of formation (proportional to organ metabolic rate)
rate of removal (proportional to organ blood flow)
describe the effects of increased metabolism or decreased blood flow in an organ
increased concentrations of vasodilator metabolites > local arteriolar dilation > decrease in vascular resistance > improved O2 delivery to organs
do changes in vascular resistance in one organ affect TPR?
nah gurl
what are some examples of vasodilator metabolites
adenosine K+ lactic acid H+ CO2
how is adenosine formed
levels rise when ATP formation is impaired
freely diffuses out of the cell
how is K+ increased
when frequency of action potentials increases, interstitial concentration of K+ rises
how does K+ cause relaxation
local hyperkalemia causes hyperpolarization of arterioles > decreases Ca2+ influx to vascular SM > relaxation
how are lactic acid, H+, and CO2 increased
increase when O2 demand exceeds O2 availability
actions of all vasodilator metabolites
decrease Ca2+ levels within vascular SM > relaxation > increased arteriolar radius > decreased vascular resistance > increased blood flow
what is active hyperemia?
as metabolic rate increases, blood flow increases due to local arteriolar dilation caused by increased interstitial levels of vasodilator metabolites
increase in blood flow is proportional to increase in metabolic activity
what is reactive hyperemia?
blood flow is transiently increased following a brief period of ischemia
degree and duration of increased flow are proportional to duration of occlusion
why does arteriolar dilation occur during the period of occlusion in reactive hyperemia?
- decreased stretch of arterioles (myogenic)
2. accumulation of metabolic vasodilators in interstitial fluid due to a decreased rate of removal w/ no blood flow
what length of ischemia does it take to get a reperfusion injury?
30 min
why does reperfusion injury occur?
during ischemia, enzymatic changes occur in the tissue which cause reactive oxidants to be formed when oxygen delivery increases at the time of reperfusion
ROS inactivate NO, increase endothelin 1, and damage endothelial cells
what is the result of reperfusion?
microvascular inflammation
arteriolar constriction
how does PCO2 affect cerebral blood flow (CBF)
increased PCO2 = increased CBF
highly sensitive to small changes in PCO2
how does PO2 affect CBF
CBF changes very little when arterial PO@ changes over normal range 80-120 mmHg
at what PO2 is cerebral arteriolar dilation triggered to increase flow
below 50 mmHg
begins to drop rapidly after this pt due to shape of oxygen dissociation curve
why does CO2 have such an effect on cerebral arterioles?
importance of maintaining pH in brain nearly constant as to not depress neuronal activity
how is CO2 removed from brain
blood flow
is CO2 is low, arteriolar constriction occurs to reduce blood flow and thus rate of removal of CO2
determinants of myocardial O2 demand
contractility
intraventricular pressure
heart rate
EDV
which determinant of myocardial O2 demand is most costly?
contractility
100% increase = 200% increase in O2 consumption
which determinant of myocardial O2 demand is least costly?
EDV
100% increase = <5% increase in O2 consumption
why is the splanchnic bed unusual?
the portal circulation transports blood from one capillary bed (stomach, spleen, intestine, pancreas) to another capillary bed (liver)
discuss the blood supply to the liver
dual supply
oxygenated blood through hepatic artery 20%
deoxygenated blood through portal vein 80%
what regulated GI blood flow
hormones and neural reflexes
increased parasympathetic activity = increased blood flow
increased sympathetic = decreased blood flow (due to constriction)
