Microcirculation Flashcards
What is the role of pre capillary sphincters
These rings of smooth muscle will relax to allow blood into the true capillaries, and contact to force blood through thoroughfare channels, shunts
How are PCS’s regulated?
AUTOREGULATION
So things that can cause relaxation: low O2; lactic acid release; NO and prostaglandins; raised K+ or H+ in interstitium
Stupid but want to have, how wide are capillaries roughly?
8 microns ( 1 RBC)
What are the three ways of transcapillary exchange?
Diffusion
Filtration
Pinocytosis
What factors influence Starlings Law of ultrafiltration
permeability; Pc; Pi; colloid osmotic pressure (capillary and intersitium)
Is hydrostatic pressure minus osmotic pressure
What are the four filtration pressures?
Interstitial fluid hydrostatic pressure: practically zero along the capillary
Capillary hydrostatic pressure: Highest at the arterial end and diminishes (30 to 15)
Blood colloid osmotic: osmotic pressure created by large blood proteins eg albumin. (inward pull)
IF colloid pressure: osmotic pressure caused by proteins in the interstitium, outwards pull)
Due to the filtration pressures what are the differences at the arterial and venous ends?
Arterial: Net filtration
Venous: Net reabsorption
How does altering resistance affect a capillaries pressure?
Upstream: reduces the pressure, less filtration
Downstream: Increases pressure and filtration
How does heart failure cause oedema?
Low CO will result in hormonal and neural chnages, so fluid retention (due to poorly perfused kidneys)
This will increase end diastolic pressure, central venous pressure and capillary pressure so more filtration
How can the following alter filtration and reabsorption? Vasoconstriction Vasodilation Heart failure Dehydration Hypoproteinaemia
Vasoconstriction: ^ra; decrease capillary pressure, more absorption
Vasodilation: decrease in ra, ^Pc; more filtration
Higher CVP means more filtration
Dehydration means greater BCOP, so more absorption
hypoproteinaemia: low BCOP, more filtration
