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Capillary Exchange
Capillary exchange is the exchange of nutrients and other materials from the blood into the tissues. This process takes place in the capillary network, which is made of venous and arterial ends. Water and other molecules, like glucose, leave the bloodstream through the arterial end. On the venous end, water reenters the bloodstream, bringing along waste molecules. This paper discusses how capillary exchange works on the arterial and venous ends, respectively.
Blood hydrostatic pressure refers to the outward force exerted by blood restricted within blood vessels. Capillary hydrostatic pressure (CHP) at the arterial end is more than the interstitial fluid hydrostatic pressure (IFHP). As a result of the higher blood pressure than the osmotic pressure, water, glucose, and amino acids are forced out of the blood into the interstitial space. The red blood cells and a significant proportion of plasma proteins do not leave the capillaries because they have larger molecules.
On the venous end, the blood pressure is in the capillaries is lower compared to the osmotic pressure. The blood pressure on this end is lower than the arterial end blood pressure since the capillaries on the venous side have greater cross-sectional areas than the arterial end. The plasma proteins that remain in the blood due to their large molecules account for the higher colloidal concentration in the blood than the tissue fluid. As a result, water from the interstitial space is reabsorbed into the capillaries – bringing along dissolved waste molecules. The colloidal concentration in the blood causes blood colloidal osmotic pressure (BCOP), while the interstitial colloidal proteins concentration is responsible for interstitial fluid colloidal osmotic pressure (IFCOP). The difference between BCOP and IFCOP accounts for the reabsorption of the waste molecules dissolved in water.