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Selective Reabsorption

Click here to see a chart overviewing the entire urine formation process

Click here to see a visual diagram overviewing the entire urine formation process

When the glomerular filtrate exits the Bowman's Capsule,it enters the proximal convoluted tubule.Passive and active reabsorption occur here.This tubule contains many microvilli which increase the surface area for the reabsorption. The cells surrounding this tubule contain numerous mitochondria for the active reabsorption. It's called selective reabsorption because only substances which are recognized by carrier proteins are actively reabsorbed into the peritubular capillaries. In passive reabsorption,the nutrients diffuse back into the blood.Also,some of the sodium ions are passively and actively transported into the blood;therefore,some of the chlorine ions passively follow.Because these ions cause a greater solute concentration,most of the water will go back into the blood stream by osmosis.Since the peritubular capillaries surround the nephron,this process occurs throughout the entire nephron.

Therefore,filtrate in this tubule is divided into two categories:that which is reabsorbed and that which isn't reabsorbed.

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