<P> Many types of medications are secreted in the proximal tubule . Further reading: Table of medication secreted in kidney </P> <P> Most of the ammonium that is excreted in the urine is formed in the proximal tubule via the breakdown of glutamine to alpha - ketoglutarate . This takes place in two steps, each of which generates an ammonium anion: the conversion of glutamine to glutamate and the conversion of glutamate to alpha - ketoglutarate . The alpha - ketoglutarate generated in this process is then further broken down to form two bicarbonate anions, which are pumped out of the basolateral portion of the tubule cell by co-transport with sodium ions . </P> <P> Proximal tubular epithelial cells (PTECs) have a pivotal role in kidney disease . Two mammalian cell lines are commonly used as models of the proximal tubule: porcine LLC - PK1 cells and marsupial OK cells . </P> <P> Most renal cell carcinoma, the most common form of kidney cancer, arises from the convoluted tubules . </P>

Water absorption from the proximal tubule is mainly driven by the active reabsorption of na+