Your kidneys

Kidney Functions

The Kidneys are two bean-shaped organs located in the back on either side of the spine just below your rib cage. Each kidney is about the size of an adult fist and the longest dimension is 9 to 11 centimeter.

The kidneys have an important function of filtering waste and removing excess fluid out of the blood, balancing minerals and helping to control blood pressure.

Healthy kidneys filter about half a cup of blood every minute, removing wastes and access water to make urine. The urine flows from the kidneys to the bladder through two thin tubes of muscle called ureters, one on each side of your bladder. This process produces about 1 to 2 quarts (half a gallon) of urine per day. The bladder stores the urine before exiting out of your body.

Importance of the Kidneys

Your kidneys perform many complex and vital functions that keep the rest of the body in balance. Without this balance, nerves, muscles, and other tissues in your body may not work normally. Your body needs kidney function to maintain healthy balance and to survive. For example, kidneys:

  • Purify blood by removing wastes and extra water.
  • Filter blood by keeping good, beneficial compounds while removing others
  • Remove acid that is produced by the cells of your body
  • Release hormones that help regulate blood pressure
  • Control the production of red blood cells, which carry oxygen throughout the body
  • Make vitamins that control growth
  • Maintain a healthy balance of water, salts, and minerals—such as sodium, calcium, phosphorous, and potassium—in your blood

How the Kidneys Work

Each of your kidneys is made up of about a million filtering units called nephrons. Blood flows into your kidney through the renal artery. This large blood vessel branches into smaller and smaller blood vessels until the blood reaches the nephrons.

Each nephron has a small blood vessel that brings in unfiltered blood, a glomerulus (Greek word meaning filter; plural form of the word is glomeruli) that filters the blood, a tubule that caries away filtered waste materials in the urine, and a small blood vessel that returns filtered blood to the body. The nephrons work through a two-step process: the glomerulus filters your blood, and the tubule returns needed substances to your blood and removes wastes.

As blood flows into each nephron, it enters a cluster of tiny blood vessels—the glomerulus. The thin walls of the glomerulus allow smaller molecules, wastes, and fluid—mostly water—to pass into the tubule. Larger molecules, such as proteins and blood cells, stay in the blood vessel.

A blood vessel runs alongside the tubule. As the filtered fluid moves along the tubule, the blood vessel reabsorbs almost all of the water, along with minerals and nutrients your body needs. The tubule helps remove excess acid from the blood. Most of the water and other substances that filter through your glomeruli are returned to your blood by the tubules. The filtered blood then flows out of your kidney through the renal vein. The remaining fluid and wastes in the tubule become urine.

 

Your blood circulates through your kidneys many times a day. In a single day, your kidneys filter about 150 quarts of blood. Most of the water and other substances that filter through your glomeruli are returned to your blood by the tubules. Only 1 to 2 quarts become urine.