Ammonia produced in kidney cells can diffuse out of the cell, but only in its un

Question

Ammonia produced in kidney cells can diffuse out of the cell, but only in its unprotonated (NH_3) form. (a) Explain. (b) The NH^+_4 ion, however, can exit the cell in exchange for another ion. What ion is most likely involved? Kidney cells excrete H+ and reabsorb HCO^-_3, from the filtrate. The movement of each of these ion* is thermodynamically unfavorable. However, the movement of each becomes possible when it is coupled to another, thermodynamically favorable ion transport process. Explain how the movement of other ions drives the transport of H+ and HCO^-_3.

Explanation / Answer

4) The proximal tubules are the main site for ammonia genesis. The ammonia so produced can be excreted in urine or returned to systemic circulation through renal veins. Ammonia produced diffuse passively into the lumen and are protonated (NH4). NH4 are unable to diffuse. So, only unprotonated ammonia can diffuse out of the cell.

b) The NH4+ ion can exit the cell in exchange for hydrogen ions.

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