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The kidneys

Men and women discussing kidney cancer

This page tells you about the kidneys and what they do. There is information about

 

A quick guide to what's on this page

The kidneys

The kidneys are two bean shaped organs about the same size as a fist. They are near the middle of the back, one on either side of the spine. The kidneys are part of the body system called the urinary system. They filter the blood. As the blood passes through them, they collect waste products and unneeded water and turn them into urine. This happens in tiny tubes called nephrons. Each kidney has about 1 million nephrons.

The urine drains into the bladder down a tube called the ureter. There are 2 ureters – one from each kidney. Another tube called the urethra carries the urine from the bladder out of the body.

Hormones

The kidneys also produce three important hormones

  • Erythropoietin (EPO) tells the bone marrow to make red blood cells
  • Renin regulates blood pressure
  • Calcitriol (a form of Vitamin D) helps the intestine to absorb calcium from the diet

The adrenal glands

Above each kidney is a small gland called the adrenal gland. The adrenal glands make several hormones that are vital for life. If you have a kidney removed, you may have the adrenal gland above it removed too. You can manage perfectly well with one adrenal gland, but if both are removed you will need to take hormone tablets every day.

 

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Where the kidneys are

The kidneys are two bean shaped organs about the same size as a fist. They are near the middle of the back, one on either side of the spine.

Diagram showing the female urinary system

The kidneys are part of the body system called the urinary system. This system filters waste products out of the blood and makes urine. It is made up of the

  • Kidneys
  • Ureters
  • Bladder
  • Prostate (in men)
  • Urethra
 

The kidneys’ blood supply

The kidneys have a very rich blood supply. The blood needs to pass through in large amounts so that the kidneys can filter it well and remove all the waste products. The main blood supply carrying blood to each kidney is called the renal artery.

There are also large blood vessels carrying the cleaned blood away from each kidney. These are called the renal veins.

Diagram showing the parts of a kidney

 

What the kidneys do

As blood passes through the kidneys, they collect waste products and unneeded water and turn them into urine. 

Inside the kidney, very small networks of tubes called nephrons filter the blood. Each kidney has about 1 million nephrons. Inside the nephrons, waste products move from the small blood vessels (the capillaries) into the urine collecting tubes. So as the blood passes through the blood vessels of the nephron, all unwanted waste is taken away. Any chemicals needed by the body are kept or returned to the bloodstream by the nephrons. In this way, the kidneys help to regulate the levels of chemicals in the blood such as sodium and potassium, and they keep the body healthy.

Diagram showing how the kidneys work

The urine gathers in an area called the renal pelvis at the centre of each kidney. From here it drains down a tube called the ureter and into the bladder. There are 2 ureters, one from each kidney. Another tube called the urethra carries the urine from the bladder out of the body.

 

Hormones from the kidneys

As well as filtering waste products, the kidneys produce three important hormones

  • Erythropoietin (EPO), which tells the bone marrow to make red blood cells
  • Renin, which regulates blood pressure
  • Calcitriol (a form of Vitamin D), which helps the intestine to absorb calcium from the diet, and so helps to keep the bones healthy
 

The adrenal glands

Above each kidney is a small gland called the adrenal gland (ad renal means next to the kidney). 

The adrenal glands make hormones. They make

  • A natural steroid hormone called cortisol
  • A hormone called aldosterone that helps to regulate the body’s water balance
  • Adrenaline
  • Another adrenaline like hormone called noradrenaline

If you have a kidney removed, you may have the adrenal gland above it removed too. This depends on where in your kidney the cancer is. If there is any chance that cancer cells could be left behind with your adrenal gland, then your surgeon will remove it.

The adrenal hormones are vital for life. You will be perfectly well with only one adrenal gland. Your other one will make all the hormones you need. If you have both kidneys and adrenal glands removed, you will need to take hormone tablets every day.

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Updated: 3 January 2014