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Capillaries and Exchange Nutrients

How does exchange of nutrients, wastes and gasses occur at the capillary level? What two pressures are involved and how do they create a difference in net pressure from the arterial end to the venous end of the capillary? Be specific.

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The capillaries offer a huge surface area for exchange of nutrients, water, oxygen, carbon dioxide, waste materials, etc. between the plasma and the interstitial space around the cells. While small molecules (like those in the previous sentence) can easily move across capillary walls, usually plasma proteins and blood cells are trapped inside the capillaries. The movement of water containing other small molecules between the inside of the capillary and the interstitial fluid surrounding the capillary is due to a balance of forces across the capillary wall. Water and small molecules dissolved in the water move by bulk flow (like sand washed down with the river) across capillary walls. Bulk flow is a passive transport process similar to simple diffusion. Movement of water and solutes out of the capillary is called filtration, while movement of water and ...