ABSTRACT
HE FUNCTION OF the renal system in childhood is critical to the healthy function of all body systems. Body water is the largest component of body tissues, comprising 70 per cent in the infant and decreasing to 60 per cent in the adult. In the child there is a higher amount of the water outside the cells in the interstitial spaces, and there is a higher turnover of water due to increased heat production and an immature kidney function to conserve water. Infants and young children also have a larger surface area:volume ratio to lose water and heat to the outside environment. They have a larger circulating blood volume per kilogram of body weight, but their overall volume is small, so loss of blood volume has a more devastating effect and quickly affects the vital body organs. Children take in water from their diet, normally controlled automatically by their sensation of thirst, a dry mouth and the hypothalamus thirst centre stimulus. They also produce water as a by-product of their high metabolic rate. They lose water mainly through their large skin surface, their relatively longer gut and their more rapid breathing.
