proximal convoluted tubule
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The glomerular filtrate passes first into the proximal convolute tubule. The reabsorption is essentially isotonic. Here energy dependent mechanisms reabsorb all of the following constituents:

  • glucose - this mechanism is saturated when the blood glucose is more than 10 mmol/l. When this level of blood glucose is reached then glycosuria occurs.
  • amino acids
  • potassium
  • sodium - about 80% reabsorbed
  • bicarbonate - there is titratable acid and ammonium secretion
  • active secretion also transports other compounds e.g. penicillins, probenecid

There is passive reabsorption of water and chloride.