f the composition of the fluid entering and leaving the kidneys is compared, it is apparent that many of the normal plasm are handled individually, with some conservation within the tissue and readily protein and the example to illustrate this point, there is a virtual absence of glucose and appearance of a high concentration of urea in the fluid eliminated from the kidneys. This vital organ only eliminates urea, the end pr of the blood to maintain the exercises a major influence in regulating the composition internal homeostatic mechanism Acid-base, salt and water balances in the body are controlled within the kidneys by the processes of filtration, reabsorption and secretion. Changes in any of these functions will be reflected by a change in the composition of the urine. The kidneys also have an endocrine function: this organ is a major site of synthesis of several hormones including erythropoietin and 1. which influence systemic metabolic functions of the renin-angiotensin and kallekrein-kinin systems (Scicli et al. 1976). These systems are involved in the regulation of blood pressure and vasopressor activity, and of the prostaglandins Er and Fau, which exert a tegulatory effect on sodium bom tasis (Fulgraff and Brandenbusch, 1974).