Capillary Exchange 1 Flashcards
What is filtration?
Hydraulic flow down a pressure gradient
What are the 2 types of transport processes?
Endothelial transcytosis via vesicles/caveolae system
Convective transport
What capillaries require facilitated diffusion?
Brain capillaries
What is the equation for the Starling Principle?
NFP = (Pc + πif) - (Pif + πP)
NFP = (Pc - Pif) - (πP - πif)
What is the effect of arteriolar constriction on the Starling Principle?
Reduces Pc and therefore favors reabsorption
What is the effect of arteriolar dilation on the Starling Principle?
Increases Pc and therefore favors filtration
What does vasomotion create?
Variable local flow rates
What effect does arteriolar vasodilation have on capillary perfusion?
More open capillaries -> more uniform perfusion
How is absorption maintained?
Addition of fluid to extravascular space
What does the rate of fluid movement depend on?
Pressure gradient
Hydraulic conductance (Lp)
What is Lp determined by?
Number, width and length of the channels
What does the reflection co-efficient (sigma) measure?
Membrane’s molecular sensitivuty
What is the reflection co-efficient for plasma proteins?
0.9
What is the Classic Starling Equation for fluid filtration?
Qf = Lp. S. [(PC – PIF) - σ(πP - πIF)]
What are the 3 types of capillaries?
Continuous, fenestrated and discontinuous
What is greater: intracellular cleft osmotic pressure (πg) or interstitial fluid oncotic pressure (πif)
πif
What is the glycocalyx?
Semi-permeable membrane of the capillaries
What is the Michel-Weinbaum Theory of Fluid Exchange?
Qf = Lp. S. [(PC – PIF) - σ(πP - πg)]
How is filtration across continuous capillaries kept low?
Vasomotion and diminished subglycocalyx oncotic pressure
How is filtrate returned to the blood?
Lymphatic drainage into thoracic veins and absorption into lymph node capillaries
What is Fick’s Law?
Mass of solute transported per unit time
What does the Rate of Diffusion depend on?
Depends upon concentration difference, diffusion distance and physical properties of the solvent and solute
Define Fick’s Law.
Js = -DS (∆ C/ ∆ x)
Js - mass of solute diffused per unit time
∆C - concentration difference
∆ x - diffusion distance
S - surface area
D - diffusion coefficient
What does Fick’s Law depend on?
Temperature, solvent viscosity and solute size
When does free diffusion occur?
Solute diffuses through a large volume of solvent
What is the effect of membrane on diffusion?
Available area is reduced
Pathlength is longer
What is the equation for available area?
Π(r-a)^2
What is the fractional available space (ϕ, phi)?
Π(r-a)^2/Πr^2 or (r-a)^2/r^2
What is the equation for the pore area available for diffusion?
Ap x ϕ
When does hydrodynamic drag increase?
As solute radius approaches pore radius
What is D’?
Diffusion coefficient in restricted diffusion
What is diffusion process slowed by?
Increased pathlength
Limited available area
Steric exclusion
Increased hydrodynamic drag within pores
