Control of Ventilation - Trachte

Question 1

What are the major sensors controlling respiration?

Answer 1

• Central controller:
  
  • Brainstem → Pons and medulla
    
    • Pre-Bötzinger area
• Peripheral sensors:
  
  • chemoreceptors
    
    • Aortic arch, carotid bodies
• Efferent mechanisms (Lung receptors):
  
  • Pulmonary stretch receptors
  • Irritant receptors
  • Juxtacapillary receptors
  • Bronchial C fiber receptors
• Joint and muscle receptors

Question 2

Central control in the medulla (Pre-Bötzinger area) senses what?

Answer 2

• Monitors pH of CSF
  
  • influenced by arterial P_CO2
    
    • because H⁺ cannot cross the BBB
    • instead CO₂ diffuses across → converted by carbonic anhydrase
  • Plasma CO₂ is the determinant of CSF pH

Question 3

What is the normal CSF pH?

Answer 3

Normal CSF pH = 7.32

• H⁺ stimulates respiration
• Alkalosis suppresses respiration
• An aberrant CSF acidosis is eventually compensated for by HCO₃^- retention by the CSF
  
  • observed in patients with emphysema →
    
    • extremely low P_O2 and high P_CO2 → relatively low respiration rates because of this compensation

Question 4

What do peripheral chemoreceptors response to?

Answer 4

• ***Elevated P_CO (<= more sensitive to this)_​
• Suppressed P_O2 or pH

Question 5

Partial pressure of what is the most important for the control of ventilation?

Answer 5

CO₂

P_CO2 appears to be more important than O₂ or pH in control of ventilation.

Receptors/sensors are more sensitive to P_CO2.

Question 6

How does a decreased O₂ level stimulate respiration at the cellular level?

Answer 6

• Low O₂
• Stop production of ATP→ increased ADP
• Make more AMP
• AMP activates AMP-Kinase
• AMP-Kinase blocks K⁺ channels
• Cell membrane depolarizes
• Release Ca²⁺
• Action Potential
• Dopamine release

Question 7

How do pulmonary stretch receptors respond to stretch?

Answer 7

• Stretch of the lung suppresses futher inspiration
  
  • called the Herring-Breuer reflex
    
    • Relevant in Yoga
    • Slows breathing and heart rate

Question 8

What do Irritant receptors respond to?

Answer 8

• Respond to cigarette smoke and other noxious gases
• Rapidly adapting
• Produce bronchoconstriction and hyperpnea
  
  • (hyperpnea = increased depth of breathing when required to meet metabolic demand of body tissues)

Question 9

What do Juxtacapillary Receptors respond to?

Answer 9

• Respond to engorgement of capillaries and increased interstitial pressure
• May mediate shallow breathing and tachypnea associated with heart failure

Question 10

What do Bronchial C fibers respond to?

Answer 10

• Respond to noxious chemicals in bronchial circulation
  
  • Cause bronchoconstriction, mucous secretion and rapid, shallow breathing

Question 11

How do Joint and Muscle Receptors influence control of respiration?

Answer 11

• Movement of limbs increases respiratory rate
• Believed to be the stimulus for increased breathing in exercise

Question 12

What is the most relevant controller of minute-to-minute regulation of respiration normally?

Answer 12

Carbon dioxide

(Each 1 mmHg increase in P_CO2 tends to cause a 2-3L increase in ventilation if P_O2 is held constant)

Question 13

What is the ventilation response to hypoxia?

Answer 13

• If CO₂ is held constant, most individuals do not respond to hypoxia until P_O2 drops below 50 mmHg
• Exceptions:
  
  • ascent to high altitudes
  • chronic obstructive lung disease that has adapted to changes in pH caused by CO₂ retention