A. Secretion of Ammonia
B. Secretion of bicarbonate
C. Secretion of HCl
D. Absorption of Ammonia
This structure is distal tubule of kidney
Ans. is ‘a’ i.e., Secretion of Ammonia
The H+ ions secreted into the tubule are mopped up by urinary buffers present in the tubular fluid. The three important buffers are : –
i. Bicarbonate buffer : – Present in proximal segments (Proximal tubules, Thick ascending limb). It is nothing else but filtered HCO3- ions which react with H+ to form H2CO3. This is the most important buffer in proximal tubules.
ii. Phosphate buffer : – Especially important in distal tubules.
iii. Ammonia buffers : – Bind to H+ and produce ammonium ion (H+ + NH3 = NH4). The reaction with NH3 occurs in the proximal and distal tubules but the main buffering mechanism is active in distal tubule and this is the most important buffer in distal tubule