The Nephron

The kidneys’ job is to filter blood, eliminating substances that the body doesn’t require. Excess water, salt, and urea are drawn out of the circulation and sent to the bladder, where they may be eliminated from the body as urine. As this is happening, the “clean” blood leaves the kidney and returns to the bloodstream.

The nephron is responsible for most of the work. Blood is filtered to remove small materials (like urea, glucose etc.) into the tubule. These materials move through the tubule and the useful ones are selectively re-absorbed (through osmosis for water, and active transport for most other things). The remaining filtrate (which is now urine) enters the collecting duct at the end of the kidney, and from here it will be sent to the ureter which is the tube leaving the kidney