These part of the body which are only about as big as a fist giant when it comes to their ability to work. The basic function goes like filtering and cleaning the blood, producing the urine which carries liquid waste out of the body etc. The two kidneys are the major organs of the urinary system which also include ureters, bladder and urethra.
Some people are born with only one kidney. There are people who lose a kidney because of disease. And even though the fragile kidneys are protected by thick layers of fat they can be injured by a hard blow to the body. This is the reason why kidney punches are illegal in boxing. Even if a kidney from the pair is damaged it is possible to live a normal healthy life with only one kidney.
Both the kidneys do the same purification tasks ie removing waste and toxins from the body, maintaining the balance of body fluids and maintaining proper range of blood pressure. It will astonish you when you know these kidneys clean more than one million gallons of liquid in a lifetime. But one kidney can handle this task. In fact, when one kidney is removed the remaining kidney can increase in size by 50 per cent within two months to take over the whole job.