Humans have two kidneys. They are complex organs that are vital for life. The kidneys produce urine which is made up of waste products, excess mineral ions and excess water from the body.
The main job of your kidneys is to regulate the amount of water in the body and balance the concentration of mineral ions in the blood. They also get rid of waste products, especially a nitrogen-containing compound called urea. At the same time they hold on to useful substances such as glucose and protein so none is lost from the body.