10 Things Kidneys do…

1 Filtration. 

Just above a litre of blood passes both kidneys every minute and one tenth gets filtered out as fluid. Blood cells, most proteins and fat particles stay in. Water and anything smaller get squeezed out!

2 Reabsorption. 

Next, the kidneys do some fine tuning. They take back in what is useful to the body: the right amount of minerals, glucose, amino-acids and water.

3 Water balance.

Kidneys pee more when we drink more but conserves water by peeing little if we are not drinking enough.

4 Excretion 

Hundreds of waste products like urea, toxins and drugs are filtered out and not taken back. This way, the kidneys keep the inside of the body clean.

5 Acid-base balance

Our bodily functions like food metabolism produce a lot of acid. The kidneys are the only organs that gets rid of excess acid.

6 Homeostasis

The kidneys keep the environment in the body stable. It includes keeping the concentration of many chemicals in the body within a tight range.

7 Blood pressure control. 

The kidneys control blood pressure by getting rid of excess salt and releasing various hormones. If the kidneys are diseased, blood pressure goes up.

8 Erythropoeitin production 

The kidneys produce erythropoeitin (EPO) that makes the bone marrow produce red cells. Without any EPO, we become severely anaemic.

9 Vitamin D activation

Kidneys convert the vitamin D we get from food and the sun into an active form that keep our bones strong and healthy.

10 Glucose control

The kidneys help to stabilise blood sugars by controlling the loss of glucose in the urine and by making new glucose when levels go low. This is why the newest class of drugs for diabetes act on the kidneys.

10 Facts about Kidneys


The kidneys are located deep in the lower back to the left and right of the spine near the lower ribs.


Each kidney is shaped like a bean with the size of a fist. It is on average about 11cm long and 6cm wide and 150g in weight. These dimensions are obviously proportional to the person’s height.


The right kidney lies lower than the left kidney as a result of being pushed down by the liver. The right kidney is also slightly smaller than the left.


Most people are born with 2 kidneys but some healthy people can have 1 or 3 or 4 (click here and here to find out more) kidneys too!


The kidneys move up and down by a few centimetres as we breathe in and out.


The kidneys receive 20% of all the blood the heart pumps out. That is just above one thousand millilitres every minute!


Taking in all that blood flow, the kidneys filter out about 120 millilitres of fluid every minute. Don’t worry, they later reabsorb most of the fluid back in the body. After all, we normally pass just over a litre of urine a day!


Each kidney contains just over one million nephrons. A nephron is a miniature filter that receives blood, filters and reabsorbs fluid to produce urine.


Each kidney has a cap above upper pole. This is the adrenal gland which functions separately from the kidney and produces important hormones.


The kidneys shrink slowly as we get older but this process occurs faster and earlier in kidney disease. A badly shrunken kidney will barely function.