<prompt> Answer this question truthfullyWhat is the term used to describe H2PO4, which is formed when secreted H combines with HPO4- in the lumen of the late distal tubule and collecting duct?  <response>: <reason> H2PO4, which is formed when secreted H combines with HPO4- in the lumen of the late distal tubule and collecting duct, is known as a titratable acid. 