Background
The kidneys play a vital role in homeostasis, or the maintenance of constant
conditions within the body. They regulate the chemical content, the pH, and the
osmotic pressure of the blood
The kidneys form urine by the combined processes of glomerular filtration, tubular
reabsorption, and tubular secretion. Water and many chemical substances whose
molecular sizes are not too great filter out of the glomeruli and move through
nephrons and into collecting ducts. As the filtrate passes through the nephrons
some substances, such as sodium, calcium, glucose, and amino acids, are
reabsorbed, whereas other substances, such as potassium and hydrogen ions, are
secreted by the cells of the nephron tubule