Control Of Ventilation - Chemoreceptors

Question 1

Which nerve controls the diaphragm? Which nerves control the external intercostal muscles? Where in the brain are these located?

Answer 1

Diaphragm - phrenic
External intercostal muscles - intercostal nerves

Pons and medulla (respiratory centres)

Question 2

Which group of neurons are responsible for stimulating inspiratory muscles?

Answer 2

dorsal respiratory group (DRG)

Question 3

Which group of neurons are used in expiration (and how to they aid inspiration)?

Answer 3

Ventral respiratory group (VRG)

Aid inspiration - basal tone maintained in tongue, pharynx and larynx to maintain open airway

Question 4

What are the 2 classes of chemoreceptors?

Answer 4

Central chemoreceptors

Peripheral chemoreceptors

Question 5

Where are the central chemoreceptors located? What to they respond to?

Answer 5

Medulla

Respond directly to H+ (directly reflects the PCO2)
- Primary Ventilatory drive

Question 6

Where are the peripheral chemoreceptors located? What to they respond to?

Answer 6

Carotid and aortic bodies

Respond primarily to PO2 (less so PCO2) and plasma [H+]
- Secondary Ventilatory drive

Question 7

How to central chemoreceptors regulate arterial PCO2?

Answer 7

Detect changes in [H+} in the cerebral spinal fluid (CSF) surrounding the brain
o Reflex stimulation of ventilation following rise in [H+]

Question 8

How are the peripheral chemoreceptors important during hypoxia?

Answer 8

Chronic lung disease PACO2 can become chronically elevated
o Individuals desensitised to PCO2 and instead rely on PaO2 to stimulate ventilation
- peripheral chemoreceptors detect changes in arterial PO2 and [H+]
- cause reflex stimulation of ventilation following significant fall in arterial PO2

Question 9

How are peripheral chemoreceptors important during acid-base imbalance?

Answer 9

• Peripheral chemoreceptors also respond to increasing plasma [H+]
  o Often, but not always, the H+ originates from CO2
  - E.g. lactic acid
  o Plasma pH falls ([H+] increases) – ventilation stimulated “acidosis”
  - Blows off CO2 thus reducing H+

Question 10

What does hypo/hyperventilation do to acid-base balance?

Answer 10

o Hypoventilation – causes CO2 retention leading to increased [H+]
- Leads to respiratory acidosis
o Hyperventilation- blows off more CO2 leading to decreased [H+]
- Leads to respiratory alkalosis