Introduction to physiological chemistry / by Meyer Bodansky.

  • Bodansky, Meyer, 1896-1941.
Date:
1934
Catalogue details

Licence: In copyright

Credit: Introduction to physiological chemistry / by Meyer Bodansky. Source: Wellcome Collection.

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    to that of the sea water in which it lives. If the environment is changed to diluted water (not below 75 per cent of the initial concentration), the osmotic pressure of the blood changes correspondingly, the adjustment being due to the diffusion of water into the animal, as may be shown by the increase of its weight. If the concentration of the sea water is still further diminished, the dogfish dies. Obviously, it does not possess the mechanism for maintaining its own internal environment, independently of the external environment. Other organisms possess this ability to a varying degree. The conger eel, for example, can tolerate a 1 : 10 dilution of the sea water which is its natural habitat, with only a mod- erate change in the osmotic pressure of the blood. The shore crab, though normally in osmotic equilibrium with sea water, is capable of withstanding marked changes in the concentration of its environment with correspondingly smaller changes in the osmotic pressure of its body fluids. So far as we know, the osmotic pressure of the blood of mammals is practically independent of the external environment. ^ ^ In the animal organism one of the most important membranes is the capillary endothelium. Under normal conditions, it will allow every- thing but proteins to pass from the circulatory system to the tissue spaces. The proteins, then, depress the escaping tendency of the water on the circulatory side of the capillary endothelium and offer resistance to the capillary blood pressure. Where the other side contains no protein, as is the case in Bowman’s space in the glomeruli of the kidney, this depression of the escaping tendency will amount to about 30 to 40 mm. Hg, as was first shown by Starling, and the filtration of water through the capillaries of the glomeruli will encounter that much resist- ance. The fluid of the tissue spaces, on the other hand, has about half the protein content of the blood. Hence the resistance which water will encounter in filtering from capillary to tissue space should amount to only 15 to 20 mm. Hg. The protein content of the blood is lowered in certain pathological conditions, or else changes so that it is not as effective as normally in depressing the escaping tendency of water. Filtration into the tissue spaces becomes easier and edema results. This topic will be considered again in other connections. The student is referred to A. V. Hill, “Adventures in Biophysics,’’ Lecture III, “The Conception of the Steady State,” and also to the following articles: R. Margaria, “The Osmotic Changes in Some Marine Animals,” Proc. Roy. Soc. (Lon- don), B, 107, 606 (1931); M. Duval, Ann. Inst, oceanogr. Monaco, N. S., 2, 233 (1925); C. Schlieper, Z. vergl. Physiol., 9, 478 (1929); C. F. A. Pantin, J. Expt. Biol, 8, 63, 73, 82 (1931). 20/. Physiol, 19, 312 (1896).