Excretion and the kidneys
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What this model shows
The model shows far fewer particles than there are, each drawn as a symbol: blue drops are water, green hexagons glucose, orange diamonds ions, dark dots urea, purple clusters proteins and red discs red blood cells. Real urea, glucose and ions are colourless.
Each kidney has about a million nephrons. Together they make about 180 dm³ of filtrate a day, but only about 1.5 dm³ of urine leaves the body: most of the water goes back into the blood.
In a real glomerulus only about a fifth of the plasma is filtered: most of the water, glucose, ions and urea stay in the blood and leave in the vein. In a real kidney some of the urea also goes back into the blood along the tubule; the model leaves this out, and it removes a larger share of the urea on each pass than a real kidney. How the tubule takes substances back is not shown.
In the liver cell, the nitrogen-containing parts of two amino acids make one molecule of urea; the steps in between are not shown. A real protein is made of hundreds of amino acids, not five. The drawing of the body shows only the organs this investigation needs.
With reduced motion each process is shown at its start and its end.
Select an organ or a part of the kidney to read about it in the card.