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The kidneys are located in the back of the abdomen and have two important functions in the body:

• they regulate the water content in the blood
• they excrete/remove the toxic waste products of metabolism

The excretory system – structure and function

1. Blood is brought to the kidney in the renal artery which branches off the aorta.
2. The kidney regulates/controls the water and salt content and removes urea.
3. The filtered excess water, salts and urea form a liquid called urine.
4. The urine is transported to the bladder along tubes called ureters.
5. The bladder stores the urine until it is convenient to expel it from the body through the urethra.
6. The purified blood returns to the circulation through the renal vein and to the heart through the vena cava.

The kidney

This diagram shows where the renal artery enters the kidney, and where the renal vein leaves.

The kidney is packed with around a million structures called nephrons. These nephrons start in the cortex of the kidney and loop down into the medulla and back to the cortex.

The nephron regulates the level of water, and salts and removes urea from the blood.