Extracellular cellular fluid volume

Except for respiratory and dermal insensible water-vapor losses, all remaining water lost by the body contains electrolytes, mainly sodium and chloride. The normal cation and anion constituent composition of the fluid spaces is given in Table IV. In the extracellular fluid space, sodium is the major cation and chloride the major anion. Those two ions constitute 95 of the extracellular fluid osmolality. Changes in plasma sodium concentration reflect changes in extracellular fluid volume. Potassium is the major cellular cation and phosphates and proteins comprise the major anions. The total cellular osmolality (175 + 135 = 310 mosraol/kg H2O) is equal to the total extracellular osmolality (155 + 155 = 310 mosmol/kg HaO) therefore, equal total osmotic concentrations are maintained between two fluid compartments of widely different ionic contents (Table IV). 

Dehydration may result from primary water deficiency, usually because of decreased intake, but in some instances (e.g., diabetes insipidus) it may result from increased losses of water. In general, the term dehydration implies intracellular and interstitial fluid depletion, in contrast to volume depletion, which implies extracellular, and particularly intravascular, sodium and water loss. In the case of primary water deficit, cell dehydration occurs, with delayed circulatory failure from decreased circulatory volume with ongoing losses. Initially, the patient may be thirsty and possibly have some mental status changes, such as confusion. If the cellular dehydration occurs slowly, intracellular substances, referred to as idiogenic osmols, develop that firnit progressive comphcations (e.g., cerebral edema or coma). With combined water and salt deficiencies, such as might occur with gastrointestinal... 

A constant exchange of liquid substances, ions, gases can be seen between these three volumes. In the body, the main parameters of Uquid, such as pH, osmotic pressure and volume, are strictly controlled. The pH levels of the extracellular fluid and blood are the same, and are normally about 7.36. Several biological conformations of macromolecules and the catalytic activity of enzymes are dependent upon pH. The osmotic pressure of the extracellular fluid and blood plasma are similarly dependent. Hyaluronic acid of the extracellular matrix plays a very important role in maintaining these parameters within the physiological norms. As an intermediate between the external media and the cells, extracellular matrix performs the coordinative functions between the cells and different cellular structures. The functioning of the cell cytoplasmic membrane is directly dependent on the extracellular matrix. 

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