What Do Kidneys Do?
2. Reabsorb Nutrients
As filtration happens to remove waste and excess water from blood, the kidneys return some important nutrients back into the bloodstream. The reabsorption process takes place inside the kidneys nephrons. Nutrients such as water, glucose, and amino acids removed during glomerular filtration are returned into the blood through the renal tubules.
This reabsorption happens through passive transfer, where the nutrients move from the place of high concentration in the proximal tubule into the capillaries surrounding the tubule where they are in lower concentration. In the case where larger molecules get into the urine during the passive transfer, their electrolyte polarity determines reabsorption. Ionized substances remain in the tubule to be excreted as urine while lipid soluble substances are reabsorbed into the blood.
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