WATER AMOUNT IN BODY

It is the most abundant single constituent of the body.

Water forms 75% of total body mass in a newborn, 60% in a lean adult male and 50% in an adult female.

In obese people the water content of the body is about 10% less. It is the medium in which body solutes are dissolved and most of the metabolic reac tions take place.

The body water is divided into intracellu lar and extracellular compartments.

SOURCES OF BODY WATER

Drinking water and beverages.

Water in food.

Tissue oxidation: each 1,000 calories pro duced in the body from the oxidation of foodstuff results in the production of 100 /140 ml. of water.

LOSS OF BODY WATER

Urinary excretion is about 800 to 2000 ml/ day with a normal intake of 2L of water/ day.Pulmonary loss (through breathing) is about 400 ml/day.

Fecal excretion is about 50-200 ml/day: Water loss through sweating is around 10 14 L/day. Sweat contains NaCl which may also be lost during excessive sweating.

Insensible water loss from the skin (even when not sweating) is about 400 ml/day. Other possible routes are tears and milk.Vomiting and diarrheal illnesses result in loss of appreciable amount of body water which may cause dehydration

REGULATION OF WATER BALANCE

Water is regulated mainly by two mecha nisms i.e. thirst and Antidiuretic hormone (ADH).

Thirst centre is situated in the hypothal amus, which produces a desire to drink water. This centre is stimulated by hyper tonicity of the extracellular fluid and by hypovolemia as occurs in dehydration.

Thirst is due to drying and shrinking of cells in mouth and throat by the hyper tonicity of body fluids.

Hypovolemia causes decreased renal blood flow, which in turn causes release of renin from the kidneys.Renin causes the formation of angioten sin-II (renin-angiotensin system).Both hypovolemia and angiotensin-II stimulate the release of ADH from the posterior pituitary, which causes increased reabsorption of water from renal tubules.

WATER DEPRIVATION

It happens when water lost from the body is not replaced from outside. Water formed in side the body is too less to compensate the loss.

The plasma becomes hypertonic due to a decrease in volume.

The interstitial fluid enters the plasma to compensate the loss. The volume of the interstitial fluid decreases and thus it be comes hypertonic.

To compensate the interstitial hypertonic ity, the intracellular fluid comes out in the interstitial compartment producing intra cellular dehydration and also the hyper tonicity of intracellular fluid.

The intracellular dehydration produces the sensation of thirst.

If the water loss is not compensated by am ple intake of water, more severe changes take place such as;

Cellular proteins undergo breakdown and K+ ions are released in the cells.The K+ ions leave the cell and enter the interstitial fluid and then are rapidly ex creted by the kidneys.

To balance the ionic loss of intracellular K+, Na+ ions enter the cells, thus disturb ing the ionic balance and cells functions.

The clinical picture will be dry tongue,collapsed circulation and renal failure.

If water lost is still not replaced, the condition of the individual becomes worst and death may occur when 20% of body water is lost.

WATER INTOXICATION

It is the reverse of water deprivation. It is a condition in which water content of the body is increased without a proportional increase in electrolytes. It happens in the following situations. Intravenous administration of glucose solution.

SIADH (Syndrome of Inappropriate se cretion of ADH): inappropriate excess of ADH causes more water to be reab sorbed from the renal tubules and causes overload.

Symptoms are nausea, headache, incoordina tion of movements and muscle cramps.