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Unformatted text preview: e., size and number of "pores" and the thickness of the barrier). For example, fenestrated capillaries have a higher KF than continuous capillaries. Furthermore, substances such as histamine, which are released in response to tissue injury or inflammation, increase KF. The surface area (A) is related to the length, diameter, and number of capillaries available for exchange. The surface area is dynamic in vascular beds such as skeletal muscle where the number of perfused capillaries increase several-fold during exercise. To summarize: JV = KF A [(PC PT) s(pC - pT)] The expression in brackets represents the NDF. If this is positive, filtration occurs, and if negative, reabsorption occurs. For a given NDF, the JV is determined by the product of KF and A. In most vascular beds of the body, filtration occurs across the arteriolar end of the capillary and reabsorption occurs across the venular end. In general, there is net filtration across capillary beds (i.e., filtration > reabsorption) that is picked up by the lymp...
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- Fall '07
- Hydrostatic Pressure