Microcirculation
Collagen in arteries ages and become less elastic.
Precapillary sphincters present only in few tissues like liver. Dominated by local control.
A-V Anastomoses have large smooth muscle fraction. Mainly in skin. Involved in body temperature regulation.
In capillary wall:
- Tight junctions
- Fenestrations – capillaries and postcapillary venules, large molecules
- Vesicles – can carry fluid and solute
- Fused chains of vesicles – path for large solutes
Collecting capillaries – leakage site for macromolecules, major site for WBC adherance
Venules – regulate distribution of blood in circulation, mainly neural control
Law of Laplace – small vessel can withstand pressure more easily than large vessels because tension is less. T=PxR. 12 vs. 200dynes. Or S=Pxr/w
Ficks first law of diffusion: Flux = Permeability x Area x Concentration Difference
Area depends on molecule and endothelial cell
Vant Hoff and Oncotic Pressure: Pi = RT(deltaC)
Starling balance of forces: 1) flow can be induced by hydrostatic or oncotic pressure difference.
Filtration = K[(Pp-Pt)-(Pip-Pit)]
K also called the CFC, it is proportional to the size and number of pores and number of capillaries perfused. Pp runs from 32 > 15. Pt is 0. Pip is 25. Pit is 3.
Net filtration over length of capillary is 3mmHg
Proteins are not very permeable in the capillaries and the situation approaches that for an ideal osmotic system.
Reflection coefficient describes deviation from ideality.
Any force producing filtration will be positive.
Decrease in proteins causes increase in permeability.
Histamine, TNFalpha, analphylatoxins, free radicals all increase permeability.
