How do kidneys work?

How do kidneys work?

Normally, people have two kidneys, one on each side of the spine under the lower ribs. They are reddish brown in colour and shaped like kidney beans. Each kidney is about the size of your clenched fist.

One of the main jobs of the kidneys is to remove wastes from the blood and return the cleaned blood back to the rest of the body. Every minute, about one litre of blood (one fifth of all the blood pumped by the heart) enters the kidneys through the renal arteries. After the blood is cleaned, it flows back toward the heart through the renal veins.

Inside each kidney there are more than one million tiny units called nephrons. Each nephron is made up of a very small filter called a glomerulus, which is attached to a tubule. Water and waste products are separated from the blood by the filters and then flow into the tubules. Much of this water is reabsorbed by the tubules and the wastes are concentrated into urine.

The urine is collected from the tubules in the funnel-like renal pelvis and then flows through tubes called the ureters into the bladder. Urine passes out of the body through a tube called the urethra. Together, the kidneys normally make one to two litres of urine every day depending on how much you drink.

Usually, the kidneys are able to provide more than twice as much kidney function as your body needs to work well. A normal kidney can greatly increase its workload: if you were born with one kidney or if one kidney is injured or donated, the remaining kidney can work harder to keep your body healthy.