The filtering action of the kidneys is controlled by the pituitary gland. The pituitary gland
is about the size of a pea and is found below the brain, as shown inFigure19.16. The
pituitary gland is also part of the endocrine system. The pituitary gland releases hormones
which affect the ability of the kidneys to filter water from the blood.
The absorption of water back into blood is controlled by a hormone called antidiuretic
hormone (ADH). ADH is released from the pituitary gland in the brain. One of the most
important roles of ADH is to control the body’s ability to hold onto water. If a person does
not drink enough water, ADH is released and it causes the kidneys to remove more water
from the urine. The urine is more concentrated and is less in volume.
When too much fluid is present in the blood, the amount of ADH in the blood is reduced.
This increases the amount of water that filters into the nephrons. The kidneys then produce
a large volume of more dilute urine.
Figure 19.16: The pituitary gland is found directly below the brain and releases hormones
that control the production of urine. ( 2 )
Excretory System Problems
The urinary system controls the amount of water in the body, and removes wastes, so any
problem with the urinary system can badly affect many other body systems. Some common
urinary system problems are described here.
Kidney Stones
In some cases, certain mineral wastes in urine crystallize and form kidney stones like the
one shown inFigure19.17. Stones form in the kidneys and may be found anywhere in the