PSL201Y1 Lecture Notes - Hydrostatics, Extracellular Fluid, Oncotic Pressure
20 Apr 2012
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Document Summary
There are about 10-40 billion capillaries per body, most cells being within 1 mm of capillary. It is at the level of the capillaries that exchange between blood and tissue occurs. There are two types of capillaries: continuous and frenestrated. Most solutes can enter the capillaries by simple diffusion however in the brain, the blood brain barrier limits the diffusion of solutes across the membrane. Continuous capillaries: they are the most common and have small gaps between endothelial cells. They allow small water soluble molecules to move through. Fenestrated capillaries: there are large gaps between the endothelial cells forming pores or fenestrations. They allow proteins and in some cases blood cells to move through. The fluid moves in and out of capillaries by bulk flow based on pressure gradients. The movement from capillary into interstitial space is called filtration while movement from interstitial space into capillary is called absorption. There are two forces for bulk flow: hydrostatic and osmotic pressures.
