Fascinating facts about your kidneys

Your kidneys might be only the size of an adult fist, but they are hardworking little organs. Here’s what they do and how they work.

Waste elimination

Your kidneys have an important job: they clean your blood (about 4.5 to 5.5 litres). They remove toxins and extra fluids and since your blood circulates around 400 times a day, your kidneys filter about 200 litres of blood every day. That’s about 1.3 litres every minute, depending on how much you drink. Each kidney has about one million tiny filters called nephrons that help with this cleaning process

When toxins aren’t removed

The main job of the kidneys is to remove toxins from the body. When they don't work properly, these impurities build up, causing symptoms like tiredness, nausea, vomiting, swelling in the hands, feet, and ankles, confusion, cramps, itchy skin, and frequent urination. Besides filtering waste into urine, kidneys also help control blood pressure by producing important hormones, support the creation of red blood cells, and contribute to bone health.

Kidneys are “intelligent”

The kidneys are versatile and can step in to do the work of other organs, like making Vitamin D. Normally, your skin produces this important nutrient when exposed to sunlight. If your skin can’t do it, the liver takes over, and if the liver can't produce it either, the kidneys will step in. The kidneys also notice when blood pressure drops and send signals to make blood vessels tighten so you don’t feel dizzy. If your blood oxygen levels drop, they release a hormone called erythropoietin, which helps produce more red blood cells.

Adaptable organs

“Hardworking as they are, you don’t need both kidneys to filter blood efficiently,” says Dr Geoffrey Bihl, a physician and nephrologist at Mediclinic Vergelegen. In fact, if one kidney becomes unavailable, perhaps through an accident, because you were born without one, or because you have decided to donate one for a transplant, you will lose only 25% of renal function. If one kidney is removed or not working, the other kidney can work twice as hard. It may grow larger to handle the extra workload, but this usually doesn’t affect your health.

Success of transplants

If you receive a kidney through transplant, the failing kidney will not be removed from your body. Instead, the new organ will be placed within your pelvis, where it will take over the old one’s function. A kidney from a deceased donor is likely to function efficiently for 15-20 years, and a transplant from a living donor lasts, on average, five years longer. Kidney transplants are usually very successful. In the UK, 99 out of 100 patients who get kidneys from living donors are alive after one year, and 86 are still alive 10 years later.

Also, if the first transplant doesn’t work, you can have another one. In 2023, over 2 000 people in South Africa were waiting for kidney transplants. According to Transplant Education for Living Legacies (TELL), about one in eight South Africans has kidney disease.