BIOSC 1250 Lecture Notes - Lecture 13: Oncotic Pressure, Extracellular Fluid, Capillary Pressure

• School: Pitt
• Department: Biological Sciences
• Course: BIOSC 1250
• Professor: Alan Sved

Document Summary

From arterioles we move to capillaries the site of exchange between the circulatory system and the interstitial fluid [slide 1]. However, there are so, so many of them, that their combined total cross-sectional area is very great. Therefore, the velocity of blood moving through capillaries is very slow about 1/1000th of that in arteries (slide 2) [remember the distinction between blood flow (volume per time) and velocity of blood (distance per time)] Capillaries are basically a thin-walled tubes comprised of a single layer of endothelial cells. (slide 3). Passage of substances between blood plasma and interstitial fluid must be either through or between these endothelial cells by diffusion or transcytosis (or bulk flow , see below). Diffusional spaces within (fenestrations) or between the endothelial cells varies from tissue to tissue, with extremes being brain (no diffusional space; i. e. , the. "blood brain barrier) or liver (spaces large enough for even relatively large proteins).