Lecture on Control of Breathing

Introduction

• Follow-up to lectures on ventilation and exercise.
• Previous topics covered:
  • Ventilation increases with exercise intensity and CO2 production.
  • Reasons for ventilation increase: metabolic, mechanical.
  • Ventilation kinetics: Phase 1 (cardio-dynamic), Phase 2, Phase 3.
• Focus of this lecture: control of breathing.

Voluntary Control of Ventilation

• Unique to respiratory system compared to cardiovascular system.
• Can control:
  • Breath-holding.
  • Ventilation amplitude and frequency.

Ventilation Mechanics at Rest vs. Exercise

• At rest:
  • Active inspiration (diaphragm contraction).
  • Passive expiration (elastic recoil).
• During exercise:
  • Both inspiration and expiration are active.
  • Accessory muscles (intercostal, sternocleidomastoid, abs) involved.
  • Expiratory centers controlled by inspiratory centers.

Respiratory Centers

• Located in the brainstem: medulla and pons.
• Medulla's role:
  • Evaluating and prioritizing neural signals.
  • Interaction between voluntary and physiological needs (e.g., holding breath vs. need to breathe due to CO2 levels).
• Pons' role:
  • Fine-tuning and modifying breathing patterns during activities.

Chemoreceptors

• Central Chemoreceptors:

  • Located in the brain.
  • Sensitive to CO2 and H+ ions (pH changes).
  • Major feedback for ventilation control (~70%).

• Peripheral Chemoreceptors:

  • Located in carotid bodies and aortic bodies.
  • Sensitive mainly to oxygen levels.
  • Can modulate response based on CO2 and H+.
  • Contribute ~20% to ventilation control.

Other Receptors Influencing Ventilation

• Mechanoreceptors: in muscles, sensitive to tension/stretch.
• Temperature receptors: in hypothalamus.
• Pulmonary receptors: include stretch receptors, involved in reflexes like the Hering-Breuer reflex.

Summary of Breathing Control

• Integration of signals from central and peripheral chemoreceptors and other receptors.
• Pons and Medulla:
  • Work together to regulate breathing via inspiratory and expiratory centers.
  • Pons influences medulla for fine-tuning ventilation based on metabolic demands.
• Feedback loops from all parts of the body to respiratory centers.

Conclusion

• Overview of control of ventilation and its complexity.
• Upcoming lectures will focus on specific chemoreceptors (central and peripheral) and their roles during exercise.