CHAPTER 3 



Inorganic Ions 



s. ^„-- 



1 tively constant in different media; others adjust to the medium. 

 ^^ y Osmotic pressure is proportional to the total concentration of 

 solute particles, regardless of kind, and most of the osmotic pressure in the 

 blood of animals is contributed by inorganic ions. How do animals treat the 

 different elements in the inorganic salts? 



In general, living organisms tend to select certain elements and to exclude 

 others. Ninety per cent of protoplasm is composed of carbon, hydrogen, and 

 oxygen. There is little relation between abundance and availability, and only 

 indirect correlation between availability and biological utilization. Nitrogen, 

 although present in far greater amount in the atmosphere than is oxygen or 

 carbon, is much less used. In large part, the chemical properties of an element 

 determine its biological usefulness. Metals have only special uses; marine 

 animals tend to accumulate potassium in relation to sodium and to exclude 

 magnesium and sulfate. The concentration of hydrogen ions tends to be higher 

 in body fluids than in surrounding aqueous media. 



IONS IN BODY FLUIDS, EXTRACELLULAR AND INTRACELLULAR 



All cells appear to have an inorganic composition different from the fluids 

 which bathe them; that is, cell membranes selectively regulate cytoplasmic ion 

 composition. Examples of the differences between tissue and body fluid ions 

 are given in Table 8."^ Analytical separation of intracellular and extracellular 

 ions is not always possible. Data for red blood cells (Table 8) show that these 

 cells usually select potassium, although in some species (dog and cat) they 

 have relatively more sodium. The extracellular volume in frog striated muscle 

 has been estimated by histological methods to be 14.5 per cent of the total 

 muscle; if the chloride in muscle were entirely extracellular and at the concen- 

 tration of plasma chloride, the space it would occupy is 14.7 per cent in frog 

 sartorius, 14.5 per cent in rat, and 12.5 per cent in cat, in remarkable agreement 

 with the histological measurement. ^'^ The concentration of potassium, cal- 

 cium, and magnesium inside muscle fibers is higher than in muscle as a whole 

 (Table 8 ^7. n"). The concentration of potassium is 50 times greater inside 

 the fibers than in the interflbrillar space. The amount of chloride inside muscle 

 fibers is nil ■'^' ^° or is exceedingly small."'^ Microincineration data ^""^ agree 

 with the analytical data that most of the calcium and magnesium of muscle 



* Inorganic elements are here considered as ions as if in solution of comparable con- 

 centrations, although in body fluids unknown and variable amounts are bound to organic 

 molecules. 



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