Chapter 5 - Water homeostasis electrolytes and acid-base balance

Abstract

Water is a major constituent of human body representing approximately 60% of body weight in male and 55% body weight in women. Two-thirds of water in human body is associated with intracellular fluid and one-third is found in extracellular fluid. Extracellular fluid is composed mostly of plasma (containing 92% water) and interstitial fluid. Major extracellular electrolyte is sodium, while major intracellular ion is potassium. This balance is maintained by properly functioning Na, K-ATPase pump. Moreover, acid-base balance is a very important factor in normal human physiology. Normal pH of blood is 7.4, which is slightly basic. If pH is less than 7.4, the condition is called acidosis while pH above 7.4 represents alkalosis. Both acidosis and alkalosis can be classified as metabolic or respiratory. In metabolic acidosis, the value of pH is decreased along with decrease in the values of pCO2 and bicarbonate (both values below normal range), but in metabolic alkalosis, the value of pH is increased along with values of both pCO2 and bicarbonate (both values above reference range). In contrast, the value of pH is decreased, but values of both pCO2 and bicarbonate are increased during respiratory acidosis from normal values. In respiratory alkalosis, the value of pH is increased, but values of both pCO2 and bicarbonate are decreased.