How Kidneys Work

Kidneys are a critical part of your health. They “clean” your blood by removing wastes from the body through your urine, help your body to make red blood cells, and regulate blood pressure. One of the main jobs of the kidneys is to remove wastes from the blood and return the cleaned blood back to 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 into the body through the renal veins.
 
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.
 
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.

Why are kidneys so important?

Kidneys regulate water

For your body to work properly, it must contain just the right amount of water. One of the important jobs of the kidneys is to remove excess water from the body or to retain water when the body needs more.

Kidneys remove waste products and help to balance the body's minerals

Many of the substances in the blood and other body fluids must be kept at the correct level for the body to function properly. For example, sodium (salt) and potassium are minerals that come from food. The body needs these minerals for good health, but they must be kept at certain levels. When the kidneys are working properly, extra minerals, such as sodium and potassium, leave your body in the urine. The kidneys also help to adjust the levels of other minerals, such as calcium and phosphate (which are important for bone strength, growth and other functions).

Your kidneys help remove waste products, such as urea and creatinine, from your body. Urea and other wastes are made when the body breaks down protein, such as meat. Creatinine is a waste product of the muscles. As kidney function decreases, the levels of urea and creatinine in the blood increase. The creatinine level in the blood is a very useful measure of kidney function. It is measured by a simple blood test.

Kidneys produce hormones

Normal kidneys also make important chemicals in your body called hormones. These hormones circulate in the bloodstream like “messengers” and regulate blood pressure, red blood cell production and the calcium balance in your body.