Understanding the Control of Breathing

Dec 9, 2024

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.