Info

Thus, for the total capillary circulation, we find a near-equilibrium between the total outward forces, 28.3 mm Hg, and the total inward force, 28.0 mm Hg. This slight imbalance of forces, 0.3 mm Hg, causes slightly more filtration of fluid into the interstitial spaces than reabsorption.This slight excess of filtration is called net filtration, and it is the fluid that must be returned to the circulation through the lymphatics. The normal rate of net filtration in the entire body is only about 2 milliliters per minute.

Filtration Coefficient. In the above example, an average net imbalance of forces at the capillary membranes of 0.3 mm Hg causes net fluid filtration in the entire body of 2 ml/min. Expressing this for each millimeter of mercury imbalance, one finds a net filtration rate of 6.67 milliliters of fluid per minute per millimeter of mercury for the entire body. This is called the whole body capillary filtration coefficient.

The filtration coefficient can also be expressed for separate parts of the body in terms of rate of filtration per minute per millimeter of mercury per 100 grams of tissue. On this basis, the filtration coefficient of the average tissue is about 0.01 ml/min/mm Hg/100 g of tissue. But, because of extreme differences in permeabilities of the capillary systems in different tissues, this coefficient varies more than 100-fold among the different tissues. It is very small in both brain and muscle, moderately large in subcutaneous tissue, large in the intestine, and extreme in the liver and glomeru-lus of the kidney where the pores are either numerous or wide open. By the same token, the permeation of proteins through the capillary membranes varies greatly as well. The concentration of protein in the interstitial fluid of muscles is about 1.5 g/dl; in subcutaneous tissue, 2 g/dl; in intestine, 4 g/dl; and in liver, 6 g/dl.

Implanted Blood Skin capsule vessels

Implanted Blood Skin capsule vessels

Was this article helpful?

0 0
Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment