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
- 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.