microcirculation Flashcards
why is the blood flow velocity in capillaries not always the same?
it depends on the contractile state of the pre-capillary sphincters.
colloid osmotic pressure: which direction does this make fluid move?
it is driven by presence of proteins, so the fluid will move to where there is most proteins.
how does the pre-capillary sphinchter constricting affect the capillary hydrostatic pressure (Pc)?
the capillary hydrostatic pressure (Pc) decreases.
as it reduces the flow
how does the post capillary sphincter constricting or the venule constricting affect the capillary hydrostatic pressure (Pc)?
the Pc will increase
as there is a decrease in blood flow out of the capillary
why is there normally a low interstitial fluid colloid osmotic pressure?
normally not many proteins in the interstitial as the proteins are too large to leave the capillary.
what is the most important mechanism that draws the fluid back into the capillary at the venous end?
there is high capillary cllid osmotic pressure as there are normally a lot more proteins with less fluid I the venous end of the capillary.
what is the least important mechanism of fluid movement?
interstitial colloid osmotic pressure as there is not many proteins in the interstitial
as the proteins are too large to leave the capillary
if there are some proteins that did escape form the capillary, what happens to them?
they are taken away by the lymphatic system
otherwise it would cause swelling
what two things do you know to calculate fluid movement?
filtration force (mostly depends on capillary hydrostatic pressure) and the reabsorption forces (mostly depends on plasma colloid osmotic pressure)
as you go across the capillary bed what happens to the capillary hydrostatic pressure?
it decreases
as you go across the capillary bed what happens to the plasma colloid osmotic pressure?
it stays relatively the same
so which process takes place is capillary hydrostatic pressure (Pc) is greater than plasma colloid osmotic pressure?
there is net filtration
which process takes place if the capillary hydrostatic pressure is less than the plasma colloid osmotic pressure?
there is net reabsorption
what does the filtration coefficient (Kf) represent?
it is the constant that shows the permeability and surface area available for filtration
how do you work out the filtration forces?
capillary hydrostatic + interstitial osmotic
how do you work out reabsorption forces?
interstitial hydrostatic + capillary osmotic
how do you work out the rate of fluid movement
Kf(filtration forces-reabsorption forces)
what happens to filtration and reabsorption when pre capillaries constrict?
increase in reabsorption.
as increase in pre-cap. constricting decreases the Pc meaning less time for filtration and more time for reabsorption
what happens to the filtration and reabsorption when venues constrict /post cap. constrict?
increase in filtration.
Pc increases, more time for filtration and less time for absorption.
