control of breathing Flashcards
how is involuntary ventilation controlled?
- respiratory muscles are controlled by the CNS
- involved brainstem, especially the medulla
how is voluntary ventilation controlled?
- hyperventilation, holding breath, speaking and swallowing
where does voluntary ventilation occur?
- upper pons
- pneumatix centre
what does the pneumatix centre modulate and what does centre act on?
- modulates apneustic centre (lower pons)
- acts on respiratory rhythmicity centre
what happens when the apneustic centre is activated?
- acts to inhibit the respiratory centre
what respiratory group is involved in expiration?
- ventral
what respiratory group is involved in inspiration?
- dorsal
what are the two examples of protective interruption of respiratory rhythm ?
- slowly adapting pulmonary stretch receptors
- rapidly adapting pulmonary stretch receptors
what is the reflex involved in slowly adapting pulmonary stretch receptors called and what does it initiate?
- Hering- Breuer Reflex
- initiates a signal inhibiting inspiration
where are slowly adapting pulmonary stretch receptors located and when are they active?
- located within airway smooth muscle
- active when tidal volume reaches physical limitations of lung expansion
where are rapidly pulmonary stretch receptors found?
- dense in trachea and large airways
what do rapid pulmonary stretch receptors respond to and what do they initiate?
- respond to smoke, inhaled particles and cold air
- initiates reflex such as coughing and sneezing> stops bronchoconstriction
what do peripheral chemoreceptors detect ?
- detect change in chemical composition in blood
- responsive to oxygen but also react to C02 and acidity
where are peripheral chemoreceptors found and are they accessible?
- found in carotid bodies and aortic arch
- easily accessible receptors
what happens when low pp02 is detected and where are signals sent?
- potassium channels in membrane close so cell becomes depolarised
- voltage gated calcium channels open so exocytosis of dopamine vesicles
- signal to medullary centres to increase ventilation
what do central chemoreceptors respond to and what can cross the blood- brain barrier?
- respond to changes in ppC02 via changes in conc. of H+
- only C02 can cross the barrier and enter
describe control by Pa02
- decrease level of 02 only effects peripheral chemoreceptors
when does ventilation increase substantially?
- when arterial 02 reaches a value of 60mmHg
describe control by PaC02
- both central and peripheral chemoreceptors involved in response
- central more important
how is carbon dioxide a potent stimulus and what effects does it have?
- exerts its effects with smaller deviations from normal values
when can concentration of hydrogen ions stimulate breathing?
- when its source is metabolic
- independent of pC02
how many stages are involved in the control of ventilation in steady state exercise?
- three phases involved
what occurs in phase I and what is this controlled by?
- ventilation increases abruptly, in first breath after exercise has started
- controlled by neural mechanisms
what happens during phase II?
- ventilation increases gradually
what happens during phase III and what is this controlled by?
- steady state is achieved so plateaus
- controlled by chemical mechanisms
what is hyperventilation?
- when the metabolic rate stays the same but breath faster than what is needed
what is the paradox of ventilation?
- no clear stimulation that increases ventilation
- ventilation is closely matched to metabolic rate
what happens by the time blood is sampled by chemoreceptors?
- it has been restored
what drives the increase in exercise induced ventilation in phase I?
- neural mechanisms (muscle afferents, central command, learnt response)
what drives the increase in exercise induced ventilation in phase II and III?
- chemical mechanisms (PC02 and H+, plasma K+, temperature, metabolic rate
what information is needed to calculate metabolic rate?
- requires info on 02 consumption and how much C02 is produced
