Structure and function of the kidney

The kidneys are the archetypal organs of homeostasis. Their primary function is filtration and segregation. Through these processes they rebalance the continual electrolyte and chemical disturbances that derive from physiological and pathological metabolic processes. Electrolytes, hydrogen (H+) ions from metabolic acids, amino acids, fatty acids, plasma proteins, immunoglobulins, and metabolic products are either retained, reabsorbed, and recycled; or they are filtered, secreted, concentrated, and excreted. These processes convert approximately 120 ml/min of primary glomerular filtrate into 1 ml/min of urine. In addition, the kidneys play crucial roles in bone mineralization, the maintenance of cardiovascular tone, systemic blood pressure, and bone marrow synthetic function via their contribution to vitamin D production, the renin–angiotensin system, and erythropoiesis.