<prompt> The principal site of acidification of urine isLoop of henleCollecting ductDCTPCT  <response>: The cells of the proximal and distal tubules secrete hydrogen ions. Acidification also occurs in the collecting ducts. The reaction that is primarily responsible for H secretion in the proximal tubules is Na-H exchange. Na is absorbed from the lumen of the tubule and H is excreted. Ref: guyton and hall textbook of medical physiology 12 edition page number:504,505,506 