B4.064 Prework 2: Regional Circulations

Question 1

flow =

Answer 1

pressure gradient / resistance in organ

Question 2

when vasoconstrictor nerves are cute and arterioles are maximally vasodilated, how does flow increase in the skeletal muscle

Answer 2

over 20 fold

Question 3

when vasoconstrictor nerves are cute and arterioles are maximally vasodilated, how does flow increase in the heart

Answer 3

5 fold

Question 4

when vasoconstrictor nerves are cute and arterioles are maximally vasodilated, how does flow increase in the brain and liver

Answer 4

2 to 3 fold

Question 5

when vasoconstrictor nerves are cute and arterioles are maximally vasodilated, how does flow increase in the kidneys

Answer 5

only 16%

high resting blood flow

Question 6

what is the pressure gradient driving blood flow to systemic organs

Answer 6

MAP-RAP

Question 7

does the pressure gradient differ between systemic organs?

Answer 7

no, all the same

Question 8

what determines the variance in resting blood flow to organs?

Answer 8

differences in vascular resistances between organs

Question 9

what is the primary determinant of organ vascular resistance

Answer 9

changes in metabolic needs, primarily changes in tissue O2 levels

Question 10

which organ systems have the most sophisticated mechanisms for local control of blood flow

Answer 10

heart and brain

Question 11

O2 uptake in an organ =

Answer 11

blood flow * (a-v)O2

Question 12

what is (a-v)O2

Answer 12

O2 extraction

Question 13

what determines ability of an organ to extract O2

Answer 13

total surface area of perfused capillaries

Question 14

fick equation

Answer 14

CO = O2 consumption/ (a-v)O2

Question 15

how much O2 does the heart extract from oxygen?

Answer 15

as much as 75% even at rest
systemic organs only 25% at rest
coronary sinus blood content = 5 ml O2

Question 16

what controls O2 uptake in heart

Answer 16

all capillaries perfused at rest, SA cannot be increased

increased O2 uptake is dependent on changes in blood flow only

Question 17

what controls O2 uptake in kidneys

Answer 17

increase capillary surface area by opening pre capillary sphincters
renal blood flow cant increase very much (max 16%)

Question 18

what is autoregulation

Answer 18

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

Question 19

which organs exhibit autoregulation

Answer 19

brain and heart

Question 20

how is flow maintained in the heart and brain

Answer 20

at low MAP, arteriolar dilation
at high MAP, arteriolar constriction
limited by maximal dilation or maximal constriction of arterioles

Question 21

what happens in systemic arterioles with changes in arterial pressure?

Answer 21

at low MAP, arteriolar constriction due to increased SYM firing via baroreflex
at high MAP, arteriolar dilation due to decreased SYM firing via baroreflex

Question 22

what is the myogenic response?

Answer 22

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

Question 23

what is the purpose of the myogenic response?

Answer 23

increases resistance in an arteriole to minimize an increase in flow while pressure is high

Question 24

what determines interstitial concentration of vasodilator metabolites?

Answer 24

rate of formation (proportional to organ metabolic rate)

rate of removal (proportional to organ blood flow)

Question 25

describe the effects of increased metabolism or decreased blood flow in an organ

Answer 25

increased concentrations of vasodilator metabolites > local arteriolar dilation > decrease in vascular resistance > improved O2 delivery to organs

Question 26

do changes in vascular resistance in one organ affect TPR?

Answer 26

nah gurl

Question 27

what are some examples of vasodilator metabolites

Answer 27

``` adenosine K+ lactic acid H+ CO2 ```

Question 28

how is adenosine formed

Answer 28

levels rise when ATP formation is impaired | freely diffuses out of the cell

Question 29

how is K+ increased

Answer 29

when frequency of action potentials increases, interstitial concentration of K+ rises

Question 30

how does K+ cause relaxation

Answer 30

local hyperkalemia causes hyperpolarization of arterioles > decreases Ca2+ influx to vascular SM > relaxation

Question 31

how are lactic acid, H+, and CO2 increased

Answer 31

increase when O2 demand exceeds O2 availability

Question 32

actions of all vasodilator metabolites

Answer 32

decrease Ca2+ levels within vascular SM > relaxation > increased arteriolar radius > decreased vascular resistance > increased blood flow

Question 33

what is active hyperemia?

Answer 33

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

Question 34

what is reactive hyperemia?

Answer 34

blood flow is transiently increased following a brief period of ischemia degree and duration of increased flow are proportional to duration of occlusion

Question 35

why does arteriolar dilation occur during the period of occlusion in reactive hyperemia?

Answer 35

1. decreased stretch of arterioles (myogenic) | 2. accumulation of metabolic vasodilators in interstitial fluid due to a decreased rate of removal w/ no blood flow

Question 36

what length of ischemia does it take to get a reperfusion injury?

Answer 36

30 min

Question 37

why does reperfusion injury occur?

Answer 37

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

Question 38

what is the result of reperfusion?

Answer 38

microvascular inflammation | arteriolar constriction

Question 39

how does PCO2 affect cerebral blood flow (CBF)

Answer 39

increased PCO2 = increased CBF | highly sensitive to small changes in PCO2

Question 40

how does PO2 affect CBF

Answer 40

CBF changes very little when arterial PO@ changes over normal range 80-120 mmHg

Question 41

at what PO2 is cerebral arteriolar dilation triggered to increase flow

Answer 41

below 50 mmHg | begins to drop rapidly after this pt due to shape of oxygen dissociation curve

Question 42

why does CO2 have such an effect on cerebral arterioles?

Answer 42

importance of maintaining pH in brain nearly constant as to not depress neuronal activity

Question 43

how is CO2 removed from brain

Answer 43

blood flow | is CO2 is low, arteriolar constriction occurs to reduce blood flow and thus rate of removal of CO2

Question 44

determinants of myocardial O2 demand

Answer 44

contractility intraventricular pressure heart rate EDV

Question 45

which determinant of myocardial O2 demand is most costly?

Answer 45

contractility | 100% increase = 200% increase in O2 consumption

Question 46

which determinant of myocardial O2 demand is least costly?

Answer 46

EDV | 100% increase = <5% increase in O2 consumption

Question 47

why is the splanchnic bed unusual?

Answer 47

the portal circulation transports blood from one capillary bed (stomach, spleen, intestine, pancreas) to another capillary bed (liver)

Question 48

discuss the blood supply to the liver

Answer 48

dual supply oxygenated blood through hepatic artery 20% deoxygenated blood through portal vein 80%

Question 49

what regulated GI blood flow

Answer 49

hormones and neural reflexes increased parasympathetic activity = increased blood flow increased sympathetic = decreased blood flow (due to constriction)