The kidneys

The kidneys are two bean-shaped organs about the same size as a fist. They are located 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. 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

What the kidneys do

The kidneys filter the blood. As the blood passes through the kidneys, waste products and unneeded water are collected and turned into urine.

The urine is gathered in an area called the renal pelvis at the centre of each kidney. From here it 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.

Inside the kidney, the blood is filtered through very small networks of tubes called nephrons. Each kidney has about 1 million nephrons. Inside the nephrons, waste products in the blood move across from the bloodstream (the capillaries) into the urine-carrying tubes inside the nephron. These tubes are called tubules. 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 keep the body healthy.

As well as filtering waste products, the kidneys 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, and so helps to keep the bones healthy

The kidneys have a very rich blood supply. The blood needs to pass through in large quantities so that it can be filtered well, and all the waste products can be removed. 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.

Above each kidney, there 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 that helps to regulate the body’s water balance called aldosterone
• 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 have to take hormone tablets every day.