Water:
The body’s need for water is second only to that for oxygen. One can live for weeks without food, but one can’t survive without water. If we lose 10% of our body water, it causes a serious hazard and death usually occurs if the loss is 20%.
The water content of the human body varies from 50-70%. Lean individuals have a higher percentage of body water than obese individuals. Men have a higher proportion of body water than women. Infants have been higher amount of water up to 70-75% of the body weight, thus making adequate fluid intake even more critical than in adults.
Water is the main solvent of the body and therefore it is an important nutrient for our body. To understand the body’s need for water, one must understand the important inter-relationships that exist among water balance, the metabolism of sodium, potassium and chloride, the role of the kidneys and the maintenance of acid-base balance in our body.
All body tissue contain water, but its content varies widely among different tissues. For example, the approximate percentage of water in teeth is 5, fat and bones is 25 and striated muscle is 80. The water in our body can broadly be divided into two compartments:
1. Intra-cellular Water: Intra-cellular which is found within the cells. It accounts for about 45% of body weight.
2. Extra-cellular Water: It is sub-divided in:
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i. Plasma Fluid: It accounts for 5% of body weight and contains proteins.
ii. Interstitial Fluid: It representing about 15% of body weight.
Extracellular fluid also includes lymph circulation and secretions of lachrymal glands, pancreas, liver and gastrointestinal mucosa. It has a much lower concentration of proteins.
Functions of Water:
1. Water is present in each cell and acts as a cushion for all cells. Each gram of protein holds about 4g water and each gram of fat about 0.2g water. In bones, water is tightly bound. In most tissues, there is a constant interchange between intercellular and extra-cellular fluid.
2. Water is the medium of all body fluids including digestive juices, lymph, blood, urine and perspiration. All the physio-chemical changes that occur in the cells of the body. It take place in the precisely regulated environment of the body fluids. Water enters into many essential reactions, like hydrolysis that occurs in digestion. In oxidation reduction reactions, water is often the end product as in the oxidation of glucose.
3. Water is a solvent for the digestion of food. It holds them in solution and permits them to pass through the absorbing walls of the intestinal tract into the blood stream. Because nutrients and wastes are soluble in water, the nutrients are carried to the cells and wastes are removed to the lungs, kidney, gut and skin. The metabolic wastes are diluted by water, thereby preventing cellular injury.
4. Water is essential as a body lubricant. Saliva makes swallowing of food possible. The mucous secretions of the gastro-intestinal tract (GIT), respiratory and genitourinary tracts keep the linings soft and smooth, the joints are kept lubricated by the surrounding fluids.
5. Water regulates body temperature by taking up the heat produced in cellular reactions and distributing it throughout the body. About 25% of the heat is lost from lungs and skin by evaporation and perspiration. When there is an increase in body temperature, the center in the hypothalamus stimulates increased sweating and evaporation.