Physiology, Medullary Cycling and Amonium Trapping: Acid Base Tutorial, University of Connecticut Health Center

After ammoniagenesis, ammonium is taken up into the medullary interstitium via a process called medullary recycling. It is then pumped back into the tubular fluid at the level of the collecting duct, where it undergoes what is called ammonium trapping after which it is excreted.