How the Kidneys Work

Kidneys are a pair of organs shaped like kidney beans. In children, they're each about the size of the child's fist.

The kidneys' most important job is to filter liquid waste from the blood and get rid of it in the form of urine. Kidneys are part of the body's urinary system.

Each kidney contains millions of tiny filters called nephrons. The nephrons work continuously to perform several important functions:

Filtering waste from the body

The kidneys produce urine to carry the waste and extra fluid they have filtered out of your child's body. The urine travels from the kidneys through tubes called ureters to your child's bladder, where it is collected.

When your child urinates, it passes out through the urethra.

Maintaining chemical and fluid balance

The kidneys help balance the chemicals in your child's blood, such as sodium, potassium and calcium, by controlling the volume of fluid in the body.

Proper balance is necessary for other systems in the body to work well. An imbalance may affect various organ systems.

Regulating blood pressure and helping produce red blood cells

The kidneys produce hormones that help regulate blood pressure to keep the heart beating normally. They stimulate the production of red blood cells, which deliver oxygen to and remove waste from all the cells in the body.

Red blood cells grow in bone marrow. Since kidneys stimulate the production of red blood cells, kidneys also help bones stay healthy.

Learn more about the kidneys.