|Human Physiology 6/e Fox|
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Sodium and Potassium Imbalances
Extracellular fluids usually have high sodium ion concentrations, and intracellular fluid usually has high potassium ion concentrations. The renal regulation of sodium is closely related to that of potassium because active reabsorption of sodium (under the influence of aldosterone) is accompanied by secretion (and excretion) of potassium. Thus, it is not surprising that conditions involving sodium ion imbalance are closely related to those involving potassium ion imbalance.
Such disorders can be summarized as follows:
Low sodium concentration (hyponatremia). Possible causes of sodium deficiencies include prolonged sweating, vomiting, or diarrhea; renal disease in which sodium is reabsorbed inadequately; adrenal cortex disorders in which aldosterone secretion is insufficient to promote the reabsorption of sodium (Addison's disease); and drinking too much water. Possible effects of hyponatremia include the development of extracellular fluid that is hypotonic and promotes the movement of water into the cells by osmosis. This is accompanied by the symptoms of water intoxication previously described.
High sodium concentration (hypernatremia). Possible causes of elevated sodium concentration include excessive water loss by evaporation and diffusion, as may occur during high fever, or increased water loss accompanying diabetes insipidus, in one form of which ADH secretion is insufficient to maintain water conservation by the renal tubules. Possible effects of hypernatremia include disturbances of the central nervous system, such as confusion, stupor, and coma.
Low potassium concentration (hypokalemia). Possible causes of potassium deficiency include excessive release of aldosterone by the adrenal cortex (Cushing's syndrome), which increases renal excretion of potassium; use of diuretic drugs that promote potassium excretion; kidney disease; and prolonged vomiting or diarrhea. Possible effects of hypokalemia include muscular weakness or paralysis, respiratory difficulty, and severe cardiac disturbances, such as atrial or ventricular arrhythmias.
High potassium concentration (hyperkalemia). Possible causes of elevated potassium concentration include renal disease, which decreases potassium excretion; use of drugs that promote renal conservation of potassium; insufficient secretion of aldosterone by the adrenal cortex (Addison's disease); or a shift of potassium from the intracellular fluid to the extracellular fluid, a change that accompanies an increase in hydrogen ion concentration (acidosis). Possible effects of hyperkalemia include paralysis of the skeletal muscles and severe cardiac disturbances, such as cardiac arrest.
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