Biology / Unit 13 Bio 3237 short lesson, about 20 seconds
Filtration, Reabsorption, Secretion: the Three-Step Mechanism
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The idea
The nephron processes fluid in three steps: filtration forces fluid out of the blood, reabsorption returns needed substances to blood, and secretion adds waste directly into the forming urine.
In practice
Glucose is normally fully reabsorbed after filtration, so healthy urine contains none.
Where people slip
Filtration is nonselective for small molecules — selectivity happens afterward, through reabsorption and secretion.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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