This process involves the regulation of the concentration of the body fluids through control of water content and salt content of the blood. If a person loses water from their blood by excessive sweating during exercise, the following will occur; blood becomes more concentrated this is detected by the hypothalamus at the base of the brain. ADH is produced by the hypothalamus and released from the pituitary body ADH travels via the bloodstream to the kidney where it makes the cells lining the second coiled tubules and collecting ducts more permeable to water. More water is reabsorbed from the ultrafiltrate, less urine is formed, and blood becomes less concentrated. About 20% of the blood that enters the kidney is filtered, the blood enters the glomerulus and the filtrate is collected in the Bowman's capsule. Useful substances such as glucose and amino acids are reabsorbed in the proximal convoluted tubule. These will moved by diffusion and active transport. Microvilli increase the surface area through which the materials pass and there are numerous mitochondria to provide energy for the active transport of materials.

Diet a high protein diet will increase the concentration of urea in the urine due to deamination of the surplus amino acids. Some drugs, such as caffeine in tea, coffee and cola, or alcohol, depress ADH release causing the urine to become more dilute. The more a person exercises the more concentrated their urine will be due to increased loss of fluid through sweating. In cold weather less sweat is produced, so the urine is more dilute. In hot weather the reverse happens.

Glomeruli in cortex where small molecules are filtered from blood and where most are returned to the blood before it leave the kidney. The medulla helps in control of water contents of blood; pyramid is a part of the medulla in which urine drains into the pelvis. The renal vein carrying blood back to the inferior vena cava renal artery carrying blood into kidney from aorta; ureter carries urine from kidney to bladder, and the pelvis is a white region at the top of the ureter.