Homeostasis - kidneys and water balance

To understand fully how the kidneys work, it is really important to learn about the structure of the kidneys first. To remind yourself about kidney structure, revisit page 2 here.

Each kidney contains about a million tiny structures called nephrons. A nephron has a cup-shaped Bowman's capsule leading into the renal tubule. The two sections of each nephron extend across the two different regions of the kidney:

• the Bowman's capsules are found within the outer cortex region
• the renal tubules run from the cortex into the darker medulla

Placed end to end, the nephrons of one kidney would stretch about 8 km. Their function is to remove waste products such as urea and balance the water and mineral ion concentration of the blood. How does the process work?

A branch of the renal artery supplies the nephrons with blood. In the Bowman's capsule, the artery splits up into a network of capillaries called the glomerulus. These capillaries join into a single vessel again as they leave the capsule, and then split into a second set of capillaries that are wrapped around the renal tubule. The blood leaves the tubule in the renal vein.

Water regulation is controlled by Anti-Diuretic Hormone (ADH). For more information see ADH and control of the water balance.