Buffering of hydrogen ion secretion by ammonia (NH3) in the collecting tubules. Ammonia diffuses into the tubular lumen, where it reacts with secreted hydrogen ions to form NH4+, which is then excreted. For each NH4+ excreted, a new HCO3- is formed in the tubular cells and returned to the blood.
membrane into the lumen, where it combines with NH3 to form NH4+, which is then excreted. The collecting ducts are permeable to NH3, which can easily diffuse into the tubular lumen. However, the luminal membrane of this part of the tubules is much less permeable to NH4+; therefore, once the H+ has reacted with NH3 to form NH4+, the NH4+ is trapped in the tubular lumen and eliminated in the urine. For each
NH4+ excreted, a new HCO3 is generated and added to the blood.
Chronic Acidosis Increases NH4+ Excretion. One of the most important features of the renal ammonium-ammonia buffer system is that it is subject to physiologic control.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.