Water is of such great importance that it makes up almost two thirds of the human body by weight. Water is present in all the tissues of the body.
It plays a fundamental role in digestion and absorption and in the elimination of indigestible metabolic waste. Water also serves as the basis of the circulatory system, which uses blood to distribute nutrients to the entire body. Moreover, water helps maintain body temperature by expelling excess heat through the skin via perspiration and evaporation. Perspiration and evaporation of water account for most of the weight a person loses while exercising.
Water Balance and Food
In its continuous process of taking in and eliminating water, one of the most important functions of the body is to maintain a continuous equilibrium between the water that enters and the water that leaves the body. Because the body does not have an organ or other place for storing water, quantities that are lost must be continuously replenished. The human body can survive for several weeks without taking in food, but going without water for the same length of time would have tragic consequences.
The human being takes in about 2.5 to 3 litres of water per day. About half is taken in by drinking, and the rest comes from eating solid food. Some foods, such as fruits and vegetables, consist of 95 per cent water. Eggs are 90% water and red meat and fish are 60 to 70% water .
60 % OF A PERSON'S WEIGHT IS DUE TO WATER. IN GENERAL, A 10% LOSS OF WATER LEADS TO SERIOUS DISORDERS, AND A LOSS OF 20% RESULTS IN DEATH.
How thirst is controlled
Thirst is the sensation through which the nervous system informs its major organ, the brain, that the body needs water. The control centre is the hypothalamus. If the concentration of plasma in the blood increases, it means the body is losing water. Dry mouth and a lack of saliva are also indications that the body needs water.
HOW WATER IS ABSORBED
Water for the body is obtained primarily by drinking and ingesting food and through internal chemical reactions.
HOW WATER IS ELIMINATED
Water is expelled not only with urine but also with sweat, through the elimination of faeces and through evaporation from the lungs and skin.
