Formation of Urine

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  • Created by: Tripat
  • Created on: 30-10-12 18:35
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  • Formation of Urine
    • Ultrafiltration
      • Urea, along with salt, water and glucose, etc., is extracted from the blood in the kidney in this process
      • Blood passing the top of the nephron is under high pressure, so fluid is forced through the sieve-like capillaries and into the capsule.
      • This fluid is called the filtrate.
      • Much of what has been filtered out needs to be returned to the blood in a process is called selective reabsorption.
    • Selective Reabsorption
      • When the filtrate reaches the proximal convoluted tubule, sodium (Na+) and chloride (Cl?) ions, glucose, amino acids and vitamins move back into the blood.
      • They are then actively transported out of these cells and into the blood capillaries.
      • Some water follows by osmosis. Surprisingly, some unwanted urea also gets reabsorbed here.
  • It does not contain any blood cells or larger proteins, as they are too big to pass out of the capillaries and into the capsule.
    • This fluid is called the filtrate.


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