The kidneys and ureters

The kidneys are part of the urinary system. They filter the blood to remove excess water and waste products.

About the kidneys

Most people have two kidneys. They are at the back of the body. One is on each side of the back bone (spine), just underneath the ribcage.

The kidneys are part of the urinary system. The kidneys filter the blood to remove excess water and waste products. These are then made into urine (pee).

On top of each kidney, there is a small gland called the adrenal gland (see illustration below). This makes hormones.

The kidneys and adrenal glands are surrounded by a layer of fat, contained in a capsule of fibrous tissue (see illustration further down this page).


How the kidneys work

The kidneys clean the blood and keep anything the body needs. This helps control the balance of fluid, salt and minerals in the body. It also helps maintain blood pressure.

Blood goes to the kidney through a large blood vessel called the renal artery. Inside the kidney there are millions of tiny filters, called nephrons. The nephrons start in the part of the kidney called the cortex and extend into triangle-shaped areas called renal pyramids.

The nephrons filter the blood to remove waste products and any extra water, which are made into urine (pee). The ‘clean’ filtered blood goes back to the rest of the body through the renal vein.

The ureters and renal pelvis

The urine collects in an area in the middle of each kidney. This area is called the renal pelvis.


Urine then drains from each kidney through a long muscular tube called a ureter. There are two ureters – one from each kidney.

The ureters connect to the bladder, where urine is stored before being passed out of the body. Lymph nodes are part of the lymphatic system. The lymphatic system helps to protect us from infection and disease.