JAI RADHAKRISHNAN, MD: The kidney is a very important organ, and the most obvious function is that it excretes wastes that we produce from our diet and from our metabolism. What's less obvious is that it's the most important organ that controls the composition of the body fluids. In addition, it does produce a number of hormones that deal with body function.
LISA CLARK: Len, if I may ask you, what's the mechanism by which the kidneys actually remove waste from the bloodstream?
LEONARD STERN, MD: The kidney is a filtering organ, so blood is delivered to a very unique apparatus in the kidney called the glomerulus, and there, because of pressure dynamics, a component of the blood is filtered across the membrane, and the first process of creating the urine develops. In this segment of the kidney, in the glomerulus, the composition of that fluid is very similar to blood. The fluid passes through a series of tubules in a structure called the nephron, and there it's modified, heavily modified. A variety of things are reabsorbed that we need, and a variety of toxins are concentrated until the end of the kidney, the end of that nephron segment, drains into something called a papilla, then into the ureter, and then the bladder, and we have what we term "urine," which is a fluid rich in toxic wastes that is excreted.
LISA CLARK: It's a remarkably complex system, and I guess there are a lot of places where things can get hung up along the way.