PHGY 214 Lecture Notes - Lecture 4: Vascular Permeability, Lipid Bilayer, Capillary
12 May 2016
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Document Summary
Bring blood within the reach of every cell (are considered the primary site for exchange of materials between blood and tissue cells) Materials are passively exchanged across capillary walls mainly through diffusion, but also through bulk flow. Describe the characteristics that make capillaries an optimal site for exchange. Capillaries are ideally suited to enhance diffusion, in accordance with fink"s law of diffusion. Diffusion across capillary walls also depends on the walls permeability to the material being exchanged. In most capillaries, narrow, water-filled gaps, or pores, lie at the junctions between the cells. These pores permit passage of small water-soluble substances. Lipid-soluble substances such as oxygen or carbon dioxide can readily pass through the endothelial cells themselves by dissolving in the lipid bilayer barrier. The size of pores varies from organ to organ. Endothelial cells in brain capillaries have nonexistence pores to thus constitute part of the protective blood-brain barrier.
