Mechanisms of capillary exchange

171

0

HWC

■ The primary role of capillaries is to permit the exchange of nutrients and wastes between the blood and tissue cells (via interstitial fluid). ■ Oxygen and nutrients move from the blood to the cells. ■ Carbon dioxide and other wastes move from the cells to the blood. The three basic mechanisms for transport of a substance across a cell layer during capillary exchange are: ■ Diffusion. ■ Transcytosis (endocytosis coupled with exocytosis). ■ Bulk flow. Diffusion ■ Diffusion is the most important method of capillary exchange. ■ Smaller, lipid-soluble molecules move easily across endothelial cell membranes. ■ Medium-sized, lipid-insoluble (water-soluble) substances, such as glucose and amino acids, move across intercellular clefts and fenestrations. Transcytosis • This method of capillary exchange is mainly used to transport small amounts of large, lipid-insoluble (water soluble) molecules, such as large proteins. ■ Substances, packaged in vesicles, move through endothelial cells via endocytosis and exocytosis. Bulk flow • This method of exchange is the movement of large volumes of ions, molecules or particles between blood and interstitial fluid. • Bulk flow occurs when a pressure gradient pushes water and dissolved solutes out of or into the capillary. • The solution of substances pass across fenestrations and intercellular clefts. • Fenestrated capillaries allow more bulk flow. • Continuous capillaries with extensive tight junctions at their intercellular clefts allow little bulk flow. • During bulk flow, most solutes cross with water. However, formed elements in the blood (such as a red blood cell) and most proteins do not cross.

Share

Embed

Copy and paste this code into your website or blog.

Add To

You must login to add videos to your playlists.

Comments

0 Comments total

to post comments.

No comments have been posted for this video yet.