Urinary Buffers Nephron cannot produce urine at pH<45 a In order to excrete more h+, the acid must be buffered a H+ secreted into the urine tubule and combines with HPO4 2 or NH3- HPO42+H+一H2PO4 NH3+H一NH4+Urinary Buffers ◼ Nephron cannot produce urine at pH< 4.5. ◼ In order to excrete more H+, the acid must be buffered. ◼ H+ secreted into the urine tubule and combines with HPO4 2- or NH3 . ◼ HPO4 2- + H+ H2PO4 - ◼ NH3 + H+ NH4 +