Kidneys and the Nephron

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The function of the kidneys is to filter the blood to get rid of the stuff we don’t need. Urea, excess salts and excess water get removed from the blood and sent to the bladder, where they can leave the body as urine. Meanwhile the “clean” blood exits kidney and goes back into circulation.

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.

Note that in a healthy person ALL glucose will be re-absorbed (if glucose remains in the urine it may be a sign of diabetes), but MOST (not all) of the water and salts are re-absorbed.