Final answer:
Hydrogen ions in the filtrate within the collecting ducts are primarily buffered by phosphate (H₂PO₄⁻), but also by bicarbonate (HCO₃⁻) and ammonia (NH₃) forming ammonium ions.
Step-by-step explanation:
Hydrogen ions in the filtrate within the collecting ducts are buffered by the presence of several substances. Key among these are phosphate (H₂PO₄⁻, dihydrogen phosphate ion), bicarbonate (HCO₃⁻), and ammonia (NH₃, forming NH₄⁻, ammonium ion). These buffering agents help maintain the urine pH typically between 4.5 and 8.0, ensuring acid-base balance within the body. Phosphate directly buffers the hydrogen ions when they're pumped into the forming urine, while bicarbonate ions are a part of the bicarbonate buffer system although the tubule cells are not permeable to them. Ammonia produced from glutamine acts as a buffer by forming ammonium ions in the urine.