Control of breathing

Question 1

What controls ventilation?

Answer 1

The medullary respiratory rhythm generators

Question 2

What does the dorsal respiratory group aid in?

Answer 2

Inspiration

Question 3

What does the ventral respiratory group aid in?

Answer 3

Inspiration; expiration when ventilation is forced etc

Question 4

How does neural activity drive ventilation?

Answer 4

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

Question 5

What are instances of voluntary control of ventilation?

Answer 5

Hyperventilation; breath holding; speaking; swallowing

Question 6

What is the danger of hyperventilation?

Answer 6

More CO2 is breathed out than in, decreasing CO2 levels in body

Question 7

What are two protective interruptions of respiratory rhythm?

Answer 7

Slowly adapting pulmonary stretch rhythm; rapidly adapting pulmonary stretch adaptors

Question 8

How does the slowly adapting pulmonary stretch rhythm protect the body?

Answer 8

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

Question 9

How does the rapidly adapting pulmonary stretch rhythm protect the body?

Answer 9

Receptors dense in trachea and large airways detect irritant introduced to the airways; causes airways to spasm/bronchoconstrict; e.g. sneezing and coughing

Question 10

What creates ventilator drive?

Answer 10

Peripheral and central chemoreceptors

Question 11

Where are peripheral chemoreceptors located?

Answer 11

In carotid bodies and aortic arch

Question 12

What is the main stimulus of peripheral chemoreceptors?

Answer 12

P(O2)

Question 13

What occurs when low P(O2) is detected by the peripheral chemoreceptors?

Answer 13

Inhibits K+ channels and close them; membrane becomes depolarised; Ca2+ gates open; Ca2+ open; exocytosis of dopamine; dopamine signal to medullary carrier; ventilation increases

Question 14

When will ventilation increase substantially?

Answer 14

When arterial O2 falls to ~60mmHg/ % saturation of Hb becomes compromised

Question 15

Where are central chemoreceptors located?

Answer 15

Somewhere in the medulla - have not been anatomically defined

Question 16

What is the main stimulus of central chemoreceptors?

Answer 16

P(CO2)

Question 17

How do central chemoreceptors detect changes in P(CO2)?

Answer 17

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

Question 18

What is a more potent stimulus for changes in ventilation: CO2 or O2?

Answer 18

CO2, small deviations in CO2 can change ventilation much more significantly than O2 would

Question 19

What would the effect of increased metabolic H+ be on ventilation?

Answer 19

Would increase ventilation, as is independent of source of H+

Question 20

What occurs during steady state exercise?

Answer 20

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.

Question 21

What is the paradox of ventilation during exercise?

Answer 21

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

Question 22

What are the suggestions for why Phase I of ventilation during steady state exercise occurs?

Answer 22

Neural mechanisms: muscle afferents; central command; learnt response

Question 23

What are the suggestions for why Phase II and III of ventilation during steady state exercise occurs?

Answer 23

Chemical mechanisms: P(CO2) and pH oscillates; plasma K+ and catecholamines increase; temperature increase; hypoglycaemia and metabolic rate increae