hemodynamics 3 Flashcards Preview

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Flashcards in hemodynamics 3 Deck (19):
1

Fractional oxygen extraction (EO2)

1. is another application of Fick’s Principle
2. Ratio of what was used compared to the initial amount.

2

Fractional oxygen extraction (EO2) equation

Eo2 = ( [O2]a -[O2]v) / [O2]a

3

Transcapillary Transport:

Solute movement & Starling’s Law of the Capillary

4

filtration is by

hydrostatic pressure

(out of vessel)

5

reabsorption is by

oncotic pressure

(into vessel)

6

Filtration & Reabsorption =

Two opposing forces that determine solute movement

7

Net flux is a balance between

filtration and reabsorption

8

Two forces drive transcapillary flux:

1. hydrostatic pressure and
2. oncotic pressure.

9

hydrostatic pressure is

fluid pressure, which is typically just blood pressure in the capillary

10

oncotic pressure is an

osmotic force exerted by solutes, primarily in the blood

11

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

12

Hydrostatic pressure favors

filtration because Pc>Pi

13

Oncotic pressure favors

absorption because more protein in blood than interstitial fluid (πc>πi)

14

Net flux is not

constant from arterial to venous end of a single capillary

15

Net flux, filtration is favored at ____, absorption at ____

filtration favored at arterial end, absorption at venous end

16

Net flux differs in

different capillary beds — more filtration in kidney, more reabsorption in GI tract

17

Transcapillary Transport: Diffusion of Lipid-soluble molecules

1. Lipid-soluble molecules diffuse freely through cell membranes
2. Diffusion follows down concentration gradients
3. Steroid hormones, some vitamins, many drugs
4. Gases – O2, CO2, nitric oxide

18

Interendothelial Junctions

1. vary in size, density, and permeability in different tissues. 2. Bigger in lympathic capillaries.
3. Large molecules (such as proteins) generally cannot go through interendothelial junctions

19

Small lipid-insoluble molecules travel

between blood and interstitial space via gaps between capillary endothelial cells.