One Headache After Another: Physiology Edition by Taylor and Cliff

Part III – Regulation

Questions

• 3. Blood pH is normally regulated by the respiratory system to control the level of CO₂ (g) and by the urinary system to control the levels of HCO₃^- and non-volatile acids in the blood.

  

• Given the overall reaction, CO₂ (g) + H₂O (l) H₂CO₃ (aq) HCO₃^- (aq) + H⁺ (aq), what effect would each of the following have on blood pH? Explain.

  

  • a. Hyperventilating
  • b. Holding your breath for an extended period of time
  • c. Chronic diarrhea
  • d. Excessive ingestion of baking soda

• 4. One of the effects of Topamax is to inhibit carbonic anhydrase. Predict the effect of Topamax on the function of each of the following cells:

  • a. Osteoclasts (bone)
  • b. Parietal cells (stomach)
  • c. Red blood cells (blood)
  • d. Epithelial cells of the proximal tubules (kidney)

• 5. The carbonic anhydrase in proximal tubule epithelial cells are particularly sensitive to inhibition by Topamax. Use the diagram of transport in the epithelial cells of the proximal tubule provided below and your understanding of the function of the kidney to provide a step-by-step explanation of how the inhibitory action of Topamax caused the disturbances in Mary’s blood chemistry.^*

  

• 6. Predict the effect of Topamax on the pH of her urine. (Choose one below.)

  • a. Caused no change in pH
  • b. Led to a decrease in pH
  • c. Led to an increase in pH

  Explain your answer in terms of the mechanisms of acid-base handling by the kidney.

• 7. Mary has an acid-base disturbance that is being compensated for with another body system. Identify the specific type of disturbance and trace out the physiological pathway responsible for the compensating action.

• 8. The same type of acid-base disturbance occurs in all of the following circumstances. Which one is most analogous (most closely matches) Mary’s condition? Explain.

  • a. Uncontrolled diabetes mellitus
  • b. Excess administration or ingestion of an acidifying agent or drug
  • c. Chronic diarrhea

• 9. Which of the following treatments would you recommend to correct Mary’s problem? Explain what effect each treatment would have upon her blood pH.

  • a. Breathing in a paper bag
  • b. An IV containing pure HCO₃^- in an isotonic solution
  • c. Holding her breath for as long as she can
  • d. An IV containing pure ammonia in an isotonic solution

• 10. Propose a reason why Mary developed the symptoms of her acid-base disturbance while hiking which hadn’t been apparent in her normal daily routine.

*Figure based on S. Drage, D. Wilkinson. “Acid Base Balance,” Update in Anaesthesia, 13 (2001): Article 12. http://www.nda.ox.ac.uk/wfsa/html/u13/u1312_02.htm, accessed 5/12/09.

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