Question

what is a salt exchange system?

Answer 1

a complex of processes of absorption, distribution, consumption, and excretion of water and salts in animals and man. Water-salt exchange maintains constant osmotic pressure, ionic composition, and acid-base equilibrium of the body’s internal environment (homeostasis).

A man weighing 70 kg requires about 2.5 l of water per day: 1.2 l as drinking water, 1 l with food, and 0.3 l is formed in the body (1.07 g, 0.556 g, and 0.396 g of water are formed during the oxidation of 1 g of fat, carbohydrates, and proteins respectively). The total water content of the human body is over 60 percent, including 40 percent within the cells in the form of water of hydration and poorly exchangeable water, 4.5 percent in the blood vessels, and 16 percent in intercellular fluid. The body contains sulfate, phosphate, bicarbonate, Na+, K+, Ca+-, Mg++, and Cl- ions, which determine the nature of the physicochemical reactions in the tissues. The body also needs trace elements—iron, zinc, cobalt, copper, and so on—which participate in oxidation-reduction reactions, activate enzymes, and are part of vitamins and other biologically active substances. Electrolytes are absorbed in the intestine with the participation of enzymes and systems of active transport for ions. Absorbed ions enter the blood or lymph and are transported to all the cells. The extracellular and intracellular fluids differ substantially from each other in their salt composition. The K+ and Mg++ ions and the phosphates predominate in the cells, and the Na+, Ca++, and Cl- ions predominate outside the cells. This difference is maintained by the activity of biological membranes and by the binding of ions by the chemical components of the cell—for example, brain, muscle, and liver phospholipids bind more sodium than potassium. The body also has salt reserves. Bone tissue contains a great deal of calcium; various minerals, including trace elements, are deposited in the liver.

Answer 2

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