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 nephronnephron
The kidney tubule in which reabsorption of substances and the balancing of the concentration of the blood takes place. s. A nephron has a cup-shaped Bowman's capsuleBowman's capsule
The cup-shaped first part of the kidney tubule found in the outer cortex region.  leading into the renal tubulerenal tubule
The main part of the kidney tubule where reabsorption takes place, found in the medulla of the kidney. . The two sections of each nephron extend across the two different regions of the kidney:

• the Bowman's capsules are found within the outer cortexcortex
  The outer region of the kidney containing the Bowman's capsules.  region
• the renal tubules run from the cortex into the darker medullamedulla
  The inner region of the kidney containing the renal tubules.

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 concentrationconcentration
The amount of a substance (solute) in a solution. 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 glomerulusglomerulus
The knot of capillaries in the Bowman's capsule. . 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.