![]() ![]() Body fluid serves as a lubricant and as a solvent for the chemical reactions that we call metabolism it transports oxygen, nutrients, chemical messengers, and waste products to their destinations it plays an important role in the regulation of body temperature. The fluid of the body flows in arteries, veins, and lymph vessels it is secreted into specialized compartments as diverse as joints, cerebral ventricles, and the intestinal lumen it both surrounds and permeates the cells. Glossary (with audio pronunciations for selected terms).What are the characteristic clinical findings of plasma excesses and deficits of potassium, calcium, magnesium, and phosphate ions?.What physiologic and pathophysiologic conditions can lead to alterations in electrolyte intake, absorption, distribution, or excretion? How do these differ between specific electrolytes?.What capillary-level mechanisms cause edema?.Under what conditions are hyponatremia (water excess) and hypernatremia (water deficit) likely to occur, and what are the characteristic clinical findings?.Under what conditions are extracellular volume deficit and excess likely to occur, and what are the characteristic clinical findings?.What are the usual and pathologic routes of fluid exit from the body?.What regulates water and electrolyte movement between plasma and interstitial fluids? Across cell membranes?.How do the compositions of plasma and interstitial fluids differ? How are they similar?.What physiologic and pathophysiologic conditions predispose an individual to disturbances in fluid intake?.For this reason, the intracellular fluid of all the different cells together is considered to be one large fluid compartment. In fact, the composition of cell fluids is remarkably similar even in different animals, ranging from the most primitive microorganisms to humans. The fluid of each cell contains its individual mixture of different constituents, but the concentrations of these substances are similar from one cell to another. Thus, the intracellular fluid constitutes about 40 per cent of the total body weight in an "average" person. Intracellular Fluid CompartmentĪbout 28 of the 42 liters of fluid in the body are inside the 75 trillion cells and are collectively called the intracellular fluid. Therefore, when discussing the "average" body fluid compartments, we should realize that variations exist, depending on age, gender, and percentage of body fat. Because women normally have more body fat than men, they contain slightly less water than men in proportion to their body weight. This is due in part to the fact that aging is usually associated with an increased percentage of the body weight being fat, which decreases the percentage of water in the body. As a person grows older, the percentage of total body weight that is fluid gradually decreases. This percentage can change, depending on age, gender, and degree of obesity. In the average 70-kilogram adult human, the total body water is about 60 per cent of the body weight, or about 42 liters. All the transcellular fluids together constitute about 1 to 2 liters. This compartment includes fluid in the synovial, peritoneal, pericardial, and intraocular spaces, as well as the cerebrospinal fluid it is usually considered to be a specialized type of extracellular fluid, although in some cases, its composition may differ markedly from that of the plasma or interstitial fluid. There is another small compartment of fluid that is referred to as transcellular fluid. The extracellular fluid is divided into the interstitial fluid and the blood plasma. The total body fluid is distributed mainly between two compartments: the extracellular fluid and the intracellular fluid (Figure 25-1). ![]()
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