Local (Intrinsic) Control of Tissue Blood Flow

Question 1

list the 3 major principles guiding circulatory function

Answer 1

the circulatory system strives to maintain 3 things:
1. tissue blood that meets each tissue’s needs
2. cardiac output that moves into circulation all the blood returned to the heart
3. constant, normal mean arterial blood pressure (this one is the most important and is prioritized above all else!!)

Question 2

what are tissue needs that influence local blood flow? (4)

Answer 2

1. oxygen and nutrient delivery
2. removal of CO2 and H+
3. maintenance of appropriate ion concentrations
4. hormone transport

Question 3

can the body produce enough blood to meet every tissue’s demand all the time?

Answer 3

hell no! the body must regulate flow to individual tissues individually; can’t constantly provide enough flow to every tissue to always cover its needs because that would require more cardiac output than the heart can generate! (can’t run a marathon AND digest a meal at the same time)

Question 4

describe the acute phase of local blood flow control

Answer 4

seconds to minutes changes; rapid changes in local arteriolar vasodilation/vasoconstriction to maintain appropriate flow

Question 5

list the 3 mechanisms contributing to acute control of local blood flow; in what organs is local control more important?

Answer 5

1. local metabolic mechanisms
2. autoregulation (myogenic mechanism)
3. endothelium-derived vasoactive factors

local control is more important/powerful in vital organs

Question 6

what is the normal mean pressure of each artery perfusing tissue? if perfusion pressure is kept constant, what will be the result of a decrease in arteriolar vascular resistance/vasodilation?

Answer 6

100mmHg; vasodilation increases local blood flow when perfusion pressure is kept constant

Question 7

describe metabolic regulation of tissue blood flow (2)

Answer 7

1. changes in tissue metabolism dramatically alter tissue blood flow
2. decrease in O2 delivery or increase in O2 usage results in an inadequate O2 supply, which increases tissue blood flow

Question 8

describe autoregulation of tissue blood flow (4)

Answer 8

1. rapid increases in arterial perfusion/pressure increase blood flow to a tissue but
2. in most tissues within 30-60 seconds, flow returns to almost normal although perfusion pressure remains high
3. increased perfusion pressure causes reflex arteriolar vasoconstriction to decrease the flow back toward normal
4. decreased perfusion pressure causes reflex arteriolar vasodilation to increase flow toward normal

Question 9

what is the mechanism of autoregulation of tissue blood flow?

Answer 9

myogenic mechanism of autoregulation: stretch-induced vascular smooth muscle depolarization leads to calcium influx and contraction; or vice versa as lack of stretch means less calcium influx and therefor vasodilation

Question 10

is autoregulation of tissue blood flow dependent on tissue metabolism?

Answer 10

nope; occurs entirely dependently of tissue metabolism

Question 11

predict and explain the effect of change in arteriolar radius on local blood flow, assuming perfusion is held constant

Answer 11

if pressure held constant, increasing arteriolar radius (vasodilation) increases blood flow and decreasing arteriolar radius (vasoconstriction) decreases blood flow

Question 12

explain how autoregulation is important for the maintenance of stable blood flow to a tissue when metabolic demands are held constant

Answer 12

autoregulation helps maintain relatively normal tissue flows over a wide range of arterial pressures; is very precise in the brain, heart, and kidneys, but can be overridden if metabolic demands increase significantly

Question 13

describe endothelium-derived vasoactive factors in acute regulation of local tissue blood flow

Answer 13

1. capillary endothelial cells synthesize substances that affect the degree of vessel contraction/relaxation
2. nitric oxide (vasodilator): mediates upstream vasodilation after local metabolic regulation dilates smaller vessels to increase tissue flow; increased blood flow shears endothelium and NO gas is released upstream after that shear is detected
3. endothelin (vasoconstrictor): released by damaged endothelium to signal vasoconstriction that prevents extensive bleeding