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Water metabolism

The importance of water:

1) Water takes part in reactions of hydrolysis, hydration, dehydration e.c.

2) Water is universal solvent

3) Transport function

4) Thermoregulation

5) Water provides hormonal regulation

Kinds of water and its distribution depend on age:

There are free and coupled (hydrated) water; exogenic and endogenic water.

There are extracellular and intracellular water. By adults extracellular water makes up 1/3 and intracellular water does 2/3. By newborn this correlation is reverse: extracellular water is more than intracellular one. Extracellular water is mobile sector, i.e. this water participates in thermoregulation, transport and hormonal regulation. This is reserve mechanism for newborn.

Distribution of water depend on localization: 1/3 of extracellular water (20%) is divided into extracellular liquid (12%), intravessel’s one (5%), transcellular’s one – 1-3% (water of cavities). The main reserve of water is muscles (50% of total water), then skin and liver.

The way of formation of endogenic water is biologic oxidation. For example, oxidation of 100g of TAG gives 107ml of water; 100g of carbohydrates gives 55 ml of water; 100 g of proteins gives 41 g of water.

The concept of water metabolism (incl. Exchange of water between tissues and blood): sources of water are water that we drink and food stuffs (milk, milk products, watermelon, melon, cucumbers, tomatoes and other vegetables, fruits and food products. Absorption of water begins in gaster and continues in intestine.

The exchange of water between tissues and vessels occurs. This process is promoted by oncotic, ocmotic and hydrostatic pressure. In arterial ends of capillaries the hydrostatic pressure is more than oncotic and osmotic pressure and water exits from vessels into extracellular liquid and then it enters the cells. So the trophic of tissues occurs. In venous ends of capillaries hydrostatic pressure is low, but oncotic and osmotic pressure is more than hydrostatic one and water with final products of metabolism enters the vessels. So excretion occurs. The loss of 10-12% of water results in serious derangement. The loss of 20-25% of water causes the death.

The excretion of water occurs through kidneys (1.5 L), skin (0.5 L), lungs (0.5L), intestine (0.3L).

Biochemistry of erythrocytes

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