hemodynamics 3 Flashcards
Fractional oxygen extraction (EO2)
- is another application of Fick’s Principle
2. Ratio of what was used compared to the initial amount.
Fractional oxygen extraction (EO2) equation
Eo2 = ( [O2]a -[O2]v) / [O2]a
Transcapillary Transport:
Solute movement & Starling’s Law of the Capillary
filtration is by
hydrostatic pressure
out of vessel
reabsorption is by
oncotic pressure
into vessel
Filtration & Reabsorption =
Two opposing forces that determine solute movement
Net flux is a balance between
filtration and reabsorption
Two forces drive transcapillary flux:
- hydrostatic pressure and
2. oncotic pressure.
hydrostatic pressure is
fluid pressure, which is typically just blood pressure in the capillary
oncotic pressure is an
osmotic force exerted by solutes, primarily in the blood
Flux equation
Flux = k [ (Pc-Pi) - (πc - πi)]
Flux = net flux across capillary wall k = constant Pc = capillary hydrostatic pressure Pi = interstitial hydrostatic pressure πc = capillary oncotic pressure πi = interstitial oncotic pressure
Hydrostatic pressure favors
filtration because Pc>Pi
Oncotic pressure favors
absorption because more protein in blood than interstitial fluid (πc>πi)
Net flux is not
constant from arterial to venous end of a single capillary
Net flux, filtration is favored at ____, absorption at ____
filtration favored at arterial end, absorption at venous end
Net flux differs in
different capillary beds — more filtration in kidney, more reabsorption in GI tract
Transcapillary Transport: Diffusion of Lipid-soluble molecules
- Lipid-soluble molecules diffuse freely through cell membranes
- Diffusion follows down concentration gradients
- Steroid hormones, some vitamins, many drugs
- Gases – O2, CO2, nitric oxide
Interendothelial Junctions
- vary in size, density, and permeability in different tissues. 2. Bigger in lympathic capillaries.
- Large molecules (such as proteins) generally cannot go through interendothelial junctions
Small lipid-insoluble molecules travel
between blood and interstitial space via gaps between capillary endothelial cells.
