The kidneys

The kidneys are a pair of organs at the back of the abdomen that filter the blood to remove waste products, which they convert into urine. From each kidney, the urine is carried to the bladder by a tube called the ureter. When the bladder is full the urine passes out of the body through a tube called the urethra. The urethra opens immediately in front of the vagina in women and at the tip of the penis in men.