Capillary filtration coefficient
Preventing the accumulation of excess fluid in the interstitial spaces would require a 68-fold increase in fluid flow rate into the lymphatic system, an amount that is 2-5 times too much for the lymphatic vessels to carry. .
An imbalance of filtration forces at the capillary membranes of 0.3 mmHg causes a net total body filtration rate of 2 ml/min. Emphasizing the net filtration flow per mmHg unbalanced, it was found that the net filtration flow was 6.67 ml/min per mmHg for the whole body. This value is called the total body capillary filtration coefficient.
Filtration coefficients can also be expressed for individual parts of the body in terms of filtration flow per minute per mmHg per 100 grams of body tissue. On that basis, the average tissue capillary filtration coefficient is about 0.01 ml/min/mmHg/100g tissue. However, because of differences in the permeability of the capillary system in different tissues, this filtration coefficient varies more than 100-fold in different tissues. It is very small in the brain and muscles, quite large in the subcutaneous tissue, large in the intestines, and extremely large in the liver and glomeruli, where the capillary openings are either numerous or enlarged. Likewise, the permeation of proteins across the capillary membrane varies greatly, which also affects the filtration coefficient. Protein concentration in the interstitial fluid of the muscle is about 1.5 g/dl; in subcutaneous tissue, 2 g / dl; in the intestine, 4 g / dl; and in the liver, 6 g/dl.
Effect of imbalance of forces at capillary membranes. If mean capillary pressure rises above 17 mmHg, the net force that tends to push the filtrate into the interstitial space increases. Therefore, an increase in mean capillary pressure of 20 mmHg, increases the net capillary filtration pressure by 0.3 mmHg to 20.3 mmHg, a result that is 68 times higher than the true capillary filtration flow of fluid into the interstitial space at normal conditions.
To prevent the accumulation of excess fluid in the interstitial would require a 68-fold increase in the normal flow rate of fluid into the lymphatic system, an amount that is 2-5 times also too much for the lymphatic vessels. blood carried away. As a result, fluid will begin to accumulate in the interstitial space and oedema results as a result.
Conversely, if capillary pressure drops very low, net reabsorption of fluid into the capillaries will occur instead of true filtration and blood volume will increase at the site of interstitial fluid volume. The effects of an imbalance in the capillary membrane are associated with the development of different types of oedema.