Scientists Say: Kidney

The kidneys are the two organs in the abdomen that do the important work of filtering blood

They kidneys (illustrated) are a pair of bean-shaped organs in the abdomen. Blood flows into each kidney through a blood vessel called the renal artery (red). That artery branches into smaller blood vessels that feed blood into tiny filters called nephrons. Wastes filtered from the blood form urine that leaves the kidneys through tubes called ureters (brown). Clean blood leaves through the renal vein (blue).


Kidney (noun, “KID-nee”)

The kidneys are two bean-shaped organs in the body. They sit just below the ribcage on either side of the spine. In an adult human, each one is about the size of a fist.

The kidneys’ main job is to filter blood. Blood flows into each kidney through a large blood vessel called the renal artery. That artery branches into smaller vessels that feed blood into about 1 million tiny filters in the kidneys. Those filters are called nephrons. They extract extra water and other wastes from the blood. (This waste comes from normal breakdown of food.) Those wastes form urine. Urine drains from the kidneys to the bladder through thin tubes of muscle called ureters. Clean blood, meanwhile, leaves the kidney through the renal vein.

All of the body’s blood passes through the kidneys many times a day. This filtration maintains a healthy balance of water, salts and minerals in the blood. The kidneys also make hormones that control blood pressure and keep bones strong.

People can do to several things help keep their kidneys healthy. First, avoid smoking. Don’t eat too much salt. (That can throw off the balance of minerals in the blood.) Drink plenty of water. This makes it harder for kidney stones to form. (Kidney stones are crystals that form in urine and block urine flow.) Exercise can also help the kidneys. Why? Because it helps keep blood pressure down. And high blood pressure, along with diabetes, is one of the most common causes of chronic kidney disease.  

In people with chronic kidney disease, kidney function slowly gets worse over time. There is no cure. People with this condition eventually need dialysis — a treatment that filters blood for the kidneys — or a new kidney. Fortunately, people can live with just one kidney. So, it’s possible for one person to donate a kidney to another person in need.

In a sentence

One of the kidney’s many jobs is to produce a hormone that tells the bone marrow to make red blood cells.

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Maria Temming is the Assistant Managing Editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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