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Your Kidneys & How They Work

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Healthy kidneys filter about a half cup of blood every minute, removing wastes and extra 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. Your bladder stores urine. Your kidneys, ureters, and bladder are part of your urinary tract.

Illustration of a human torso showing the kidneys, ureters, bladder, and urethra.
You have two kidneys that filter your blood, removing wastes and extra water to make urine.

Why are the kidneys important?



Your kidneys also make hormones that help

Watch a video about what the kidneys do.

How do my kidneys work?


Drawing of a nephron showing that a blood vessel from the renal artery leads to the glomerulus before branching across the u-shaped tubule and leading to the renal vein.
Each nephron has a glomerulus to filter your blood and a tubule that returns needed substances to your blood and pulls out additional wastes. Wastes and extra water become urine.

The glomerulus filters your blood

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.

The tubule returns needed substances to your blood and removes wastes

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. The remaining fluid and wastes in the tubule become urine.

How does blood flow through my kidneys?

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. In the nephron, your blood is filtered by the tiny blood vessels of the glomeruli and then flows out of your kidney through the renal vein.


Drawing of one kidney with the artery bringing in blood with wastes, a vein carrying the filtered blood out of the kidney, and the ureter carrying wastes (urine) to the bladder.
Blood flows into your kidneys through the renal artery and exits through the renal vein. Your ureter carries urine from the kidney to your bladder.

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June 2018
