Coloured scanning electron micrograph (SEM) of a human kidney nephron showing a cross section of tubule. Kidney uriniferous filtration tubule (nephron). Kidneys are the filtering organs of the body that remove wastes and toxins. The main filtering units are called glomeruli and the filtered fluid passes into the specialized tubules seen here (where more water and useful substances are absorbed, concentrating the fluid). The concentrate fluid passes to the bladder as urine. The tubules have two portions, the first, called the nephron, is concerned with urine production, and the second, called collecting tubules, carries out the final concentration of urine. Along the length of the nephron are distinct morphological segments that possess specific epithelium specialized for a particular role in the formation of urine. Magnification: x600 when shortest axis printed at 25 millimetres.