Kidney glomerulus, light micrograph. This section shows the glomerulus (centre) encased in its Bowman's capsule (white arc). The glomerulus itself is a dense knot of blood capillaries where filtration of waste products from the blood takes place. The waste products are excreted in the urine. Around the Bowman's capsule are the proximal and distal tubules, where the re-absorption of useful substances back into the blood takes place. The black dots are the nuclei of the cells in the walls of the capillaries and tubules. This tissue sample is from a rat.