36 - 40 Physiology SBAs for the Primary FRCA
Question 36
A 23 year old woman known to suffer with Type I Diabetes Mellitus presents to the Emergency Department in diabetic ketoacidosis.
The medical student, who until this point has been distractedly swiping on their phone, looks up and comments,
'Ah - Kussmaul breathing', before returning to their screen.
Which of the following is false?
- Peripheral chemoreceptors are faster than central chemoreceptors
- Central chemoreceptors detect a drop in CSF pH and increase minute ventilation
- Peripheral chemoreceptors are found in the aortic arch and carotid bodies, sending afferents via glossopharyngeal and vagus nerves respectively
- Central chemoreceptors can detect smaller changes in hydrogen ion concentration than peripheral chemoreceptors
- Central chemoreceptors can recalibrate to sustained changes in pH
Answer
- Peripheral chemoreceptors are found in the aortic arch and carotid bodies, sending afferents via glossopharyngeal and vagus nerves respectively
Other way round.
- Aortic arch - vagus nerve
- Carotid bodies - glossopharyngeal
All of the other statements are true.
- Acidosis triggers peripheral chemoreceptors that increase minute ventilation as described above
- Acidosis is also buffered by bicarbonate in the blood, producing more CO2
- The CO2 can then diffuse across into the CSF, where it dissociates and produces H+ ions
- The lack of buffering capacity in the CSF makes central chemoreceptors incredibly sensitive to changes in pH
- Peripheral chemoreceptors act more quickly, but central chemoreceptors have a much stronger impact on minute ventilation
- Chronic changes in pH will cause central chemoreceptors to adapt to a new set point, hence chronic CO2 retainers will often show little increased respiratory drive despite a raised PaCO2