Kidneys

I have spent a lot of time today considering the kidney. This hasn't been entirely by choice but it has been fascinating. Who knew that you had 2.2 million nephrons in your body? Who was aware that functions such as synthesizing Vitamin D and producing red blood cells have a vital role in a fist-sized object in your body? As I was studying I was trying to consider what occupation most resmebles that of the kidney. A powerhouse, behind the scene, can function alone but much more effcient in a pair, and something that most people dont know think of until there is a problem? What is your idea? I thought of an air traffic controller or a parent!