Renal Mechanisms in Acid-Base Homeostasis

The renal mechanisms for correcting blood pH are very important. However, renal adjustments to pH change take from several hours to days to complete. Thus, we cannot expect someone with a respiratory problem to rapidly recover within an hour or two. Usually, they will be hospitalised (warded) for a few hours or days, depending on the nature of their problems, before we can hope to see some changes in our patients, and before we get to see changes to improve their blood pH values. It often takes several hours or even days if the renal component is to effect change to the altered blood pH.


GENERAL QUESTIONS

1. How does the kidney regulate blood pH?

1. The kidneys reabsorb or excrete bicarbonate, depending on blood pH.
2. Under alkaline blood pH (alkalosis), the kidneys excrete excess blood bicarbonate
3. Under acidic blood pH (acidosis), the kidneys reabsorb secreted bicarbonate, which then re-enters blood

2. What are the renal mechanisms that come into play to correct blood pH?

1. Secreting or absorbing hydrogen ions or bicarbonate
2. Controlling excretion of acids and bases
3. Generating additional buffers
4. The kidneys excrete some acids in the urine. 
5. The kidneys also produce and regulate the retention of bicarbonate. Bicarbonate will increase the blood's pH. Changes in bicarbonate concentration occur more slowly than changes in CO2, taking hours or days

SPECIFIC QUESTIONS

1. What are the renal responses to acidosis?

1. Secretion of hydrogen ions (H+)
2. Activity of buffers in renal tubular fluid - refer to text elsewhere for mechanisms
3. Removal of carbon dioxide (CO2)
4. Reabsorption of sodium bicarbonate (NaHCO3)

2. What are the renal responses to alkalosis?

1. Rate of hydrogen ion (H+) secretion at kidneys declines
2. Tubule cells do not reclaim bicarbonates in tubular fluid
3. Collecting system transports bicarbonate (HCO3-) out into tubular fluid while releasing strong acid (hydrochloric acid, HCl) into peritubular fluid