Control of breathing Flashcards
What controls ventilation?
The medullary respiratory rhythm generators
What does the dorsal respiratory group aid in?
Inspiration
What does the ventral respiratory group aid in?
Inspiration; expiration when ventilation is forced etc
How does neural activity drive ventilation?
Rapid positive feedback loop of inspiratory neurons to respiratory muscles creates a graduation in activity to protect muscles; neuron activity drops significantly to allow passive expiration, but muscles do not relax completely so that expiration is still somewhat controlled
What are instances of voluntary control of ventilation?
Hyperventilation; breath holding; speaking; swallowing
What is the danger of hyperventilation?
More CO2 is breathed out than in, decreasing CO2 levels in body
What are two protective interruptions of respiratory rhythm?
Slowly adapting pulmonary stretch rhythm; rapidly adapting pulmonary stretch adaptors
How does the slowly adapting pulmonary stretch rhythm protect the body?
When tidal volume approaches the physical limitations of the lung tissue for expansion, receptor within airway smooth muscle send signal proportional to extent to which they are interrupted, and inhibits inspiration; protects lungs by preventing over-inflation
How does the rapidly adapting pulmonary stretch rhythm protect the body?
Receptors dense in trachea and large airways detect irritant introduced to the airways; causes airways to spasm/bronchoconstrict; e.g. sneezing and coughing
What creates ventilator drive?
Peripheral and central chemoreceptors
Where are peripheral chemoreceptors located?
In carotid bodies and aortic arch
What is the main stimulus of peripheral chemoreceptors?
P(O2)
What occurs when low P(O2) is detected by the peripheral chemoreceptors?
Inhibits K+ channels and close them; membrane becomes depolarised; Ca2+ gates open; Ca2+ open; exocytosis of dopamine; dopamine signal to medullary carrier; ventilation increases
When will ventilation increase substantially?
When arterial O2 falls to ~60mmHg/ % saturation of Hb becomes compromised
Where are central chemoreceptors located?
Somewhere in the medulla - have not been anatomically defined
What is the main stimulus of central chemoreceptors?
P(CO2)
How do central chemoreceptors detect changes in P(CO2)?
Only gases can diffuse across blood-brain barrier, so CO2 inters cerebrospinal fluid; CO2 + H2O –> H2CO3 –> H+ + HCO3-; H+ enters interstitial fluid to chemoreceptors; changes in [H+] determines response
What is a more potent stimulus for changes in ventilation: CO2 or O2?
CO2, small deviations in CO2 can change ventilation much more significantly than O2 would
What would the effect of increased metabolic H+ be on ventilation?
Would increase ventilation, as is independent of source of H+
What occurs during steady state exercise?
Phase I: ventilation increases abruptly (as early as first breath of exercise); thought to be neurally controlled. Phase II: ventilation increases gradually; thought to be caused by chemical stimuli. Phase III: steady state of ventilation achieved; thought to be caused by chemical stimuli.
What is the paradox of ventilation during exercise?
Ventilation increases in the absence of a clear stimulus; arterial values do not change as we’d think: arterial P(CO2) decreases, H+ increases, and P(O2) remains fairly constant
What are the suggestions for why Phase I of ventilation during steady state exercise occurs?
Neural mechanisms: muscle afferents; central command; learnt response
What are the suggestions for why Phase II and III of ventilation during steady state exercise occurs?
Chemical mechanisms: P(CO2) and pH oscillates; plasma K+ and catecholamines increase; temperature increase; hypoglycaemia and metabolic rate increae
