Caption

Kidney, artwork. The kidney is one of a pair of organs that form urine by filtering out waste products from the blood. This filtration takes place in the nephrons (blue and white lines). These basic functional units filter out all water and soluble substances and then reabsorb only what is needed. The rest is converted into urine, which travels down the ureter (tube, lower right) to the bladder (unseen), where it is excreted.