Greg Dressler, Ph.D., Professor - Department of Pathology, University of Michigan Medical School
Kidneys function to filter the blood, removing water and many small molecules, while retaining large molecules and circulating blood cells. This is an image of the filtration apparatus of a mouse kidney, taken using a scanning electron microscope. Here you see a capillary blood vessel that is completely covered with cells that have interdigitating processes, like interlocked fingers. As blood passes through such capillaries at high pressure, fluid and small molecules are forced through the cracks between these processes (the filter) and into the urinary tubules, where it is collected and sent to the bladder for elimination.