Composition of the Body Fluids
Composition of the Body
Fluids
All these fluid spaces—plasma, interstitial, and intracellular—differ from each other in solute composition, but all have one feature in common: they are mostly water. Despite their firm appearance, animals are 70% to 90% water. Humans, for example, are approximately 70% water by weight.
Of this, 50% is cell water, 15% is interstitial fluid water, and the remaining 5% is in blood plasma. Plasma spaces serve as the pathway of exchange between the cells of the body and the outside world. This exchange of respiratory gases, nutrients, and wastes is accomplished by specialized organs (kidney, lung, gill, alimentary canal), as well as by the skin (Figure 33-1A).
Body fluids contain many inorganic and organic substances in solution. Principal among these are inorganic electrolytes and proteins. Sodium, chloride, and bicarbonate ions are the chief extracellular electrolytes, whereas potassium, magnesium, and phosphate ions and proteins are the major intracellular electrolytes (Figure 33-1B). These differences are dramatic; they are always maintained despite continuous flow of materials into and out of cells of the body. The two subdivisions of extracellular fluid—plasma and interstitial fluid—have similar compositions except that plasma has more proteins, which are mostly too large to filter through capillary walls into interstitial fluid.
All these fluid spaces—plasma, interstitial, and intracellular—differ from each other in solute composition, but all have one feature in common: they are mostly water. Despite their firm appearance, animals are 70% to 90% water. Humans, for example, are approximately 70% water by weight.
Of this, 50% is cell water, 15% is interstitial fluid water, and the remaining 5% is in blood plasma. Plasma spaces serve as the pathway of exchange between the cells of the body and the outside world. This exchange of respiratory gases, nutrients, and wastes is accomplished by specialized organs (kidney, lung, gill, alimentary canal), as well as by the skin (Figure 33-1A).
Body fluids contain many inorganic and organic substances in solution. Principal among these are inorganic electrolytes and proteins. Sodium, chloride, and bicarbonate ions are the chief extracellular electrolytes, whereas potassium, magnesium, and phosphate ions and proteins are the major intracellular electrolytes (Figure 33-1B). These differences are dramatic; they are always maintained despite continuous flow of materials into and out of cells of the body. The two subdivisions of extracellular fluid—plasma and interstitial fluid—have similar compositions except that plasma has more proteins, which are mostly too large to filter through capillary walls into interstitial fluid.
Support our developers
