The kidneys

The kidneys are two bean-shaped organs, each about the size of a fist. They are found deep inside your abdomen (belly), positioned near the middle of your back, on either side of the spine.

The kidneys are part of the body’s urinary system, which also includes the:

• ureters – tubes that take urine from the kidneys to the bladder
• bladder – a hollow sac that stores urine (wee) until you need to urinate
• urethra – a tube that takes urine from the bladder to outside the body.

An adrenal gland sits above each kidney. The adrenal glands produce a number of hormones. Although these glands are not part of the urinary system, kidney cancer can sometimes spread to them.

What the kidneys do

Filter blood – The main role of the kidneys is to filter and clean the blood. Blood flows through the renal artery into each kidney, where it is filtered through tiny networks of tubes called nephrons. The clean blood then flows out through the renal vein to the rest of the body.

Make urine – When the kidneys filter the blood, they remove excess water and waste products to make urine (wee or pee). The urine collects in an area of each kidney called the renal pelvis, and then flows through the ureters into the bladder.

Produce hormones – The kidneys also help your body control how much blood it needs. They do this by making hormones that regulate blood pressure and trigger the production of red blood cells.