Control of Respiration

Question 1

What part of the brain controls ventilation?

Answer 1

The medulla

Question 2

What are the two factors controlled by the medulla that influence total ventilation?

Answer 2

1. Tidal Volume
2. Breathing Rate

Question 3

What is the role of peripheral chemoreceptors?

Answer 3

They mediate increases in ventilation in response to

• Low arterial O2
• High arterial P_CO2
• High arterial [H⁺]

Question 4

Where are peripheral chemoreceptors located?

Answer 4

Carotid bodies

Question 5

Are peripheral chemoreceptors sensitive or insensitive to low arterial O2?

Answer 5

Relatively insensitive until P_aO2<55 Torr

Question 6

Are peripheral chemoreceptors sensitive to high levels of arterial P_CO2?

Answer 6

Arterial P_CO2: fast response to high CO2; seconds

Question 7

T/F: Peripheral chemoreceptors are the only mediator of response to metabolic acid base insults?

Answer 7

TRUE

• Peripheral chemoreceptors are the only mediator of response to metabolic acid/base insults
  
  • They are fast acting

Question 8

What are the two main classes of chemorecptors?

Answer 8

1. Peripheral Chemoreceptors
2. Central Chemoreceptors

Question 9

What do Central Chemoreceptors sense?

Answer 9

Arterial CO2 via proton receptors in the CSF

• Pathophysiology behind this: Blood brain barrier allows CO2 to pass from the capillaries-> BBB -> CSF
  
  • CO2 binds water in CSF and forms bicarb and a proton
    
    • The central chemoreceptors bind protons in the CSF and respond via changes in ventilation

Question 10

T/F: Central Chemoreceptors can sense changes in arterial [H⁺] changes?

Answer 10

FALSE

• The blood brain barrier does not allow charged molecules (H⁺) to the brain
• Recall: CO2 passes through BBB creating bicarb and [H⁺] in the CSF which is then sensed by the central chemoreceptor

Question 11

T/F: Central Chemoreceptors are slow acting

Answer 11

True- response is slow (minutes)

Question 12

What percentage of the ventilatory response to high P_aCO2 is mediated by Central Chemoreceptors?

Answer 12

• 80% of the ventilatory response to high P_aCO2 under long-term conditions
  
  • This is b/c the CSF has low buffering capacity

Question 13

What is the most important day-to-day regulator of ventilation? (Peripheral or Central Chemoreceptors)

Answer 13

Central Chemoreceptors

Question 14

Which receptor-type mediates increase in ventilation?

1. Climbing Mt. Everest
2. Ketoacidosis
3. Climbing stairs
4. Bronchitis

Multiple choise answer for each question

• Peripheral O₂ receptors, peripheral CO₂, peripheral [H⁺], or central proton receptors/CO₂ sensors

Answer 14

1. Climbing Mt. Everest - Peripheral O₂ receptor
2. Ketoacidosis - Peripheral proton receptors
3. Climbing stairs - Peripheral CO₂ receptors
4. Bronchitis - Central proton receptors/CO₂ sensors

Question 15

Vignette: High levels of CO₂ in your blood, also lead to increased [H⁺] (via CO_{2 +} H₂O rxn to bicarb and proton). High CO₂ also reduces alveolar and arterial O_2.

Question: Which chemoreceptor subtype is most important in mediating ventilation and why?

Answer 15

CO₂ sensors are the most important

Why:

• Protons are buffered quite a bit in the blood so it takes a substantial disturbance to trigger them substantially
• O₂ sensors are relatively insensitive until about 55 Torr P_aO₂ (which is pretty low)