Control of Ventilation Flashcards
what actors control ventilation?
skeletal muscles of inspiration, via the phrenic nerve (diaphragm) and intercostal nerves (external intercostal muscles)
where are the respiratory centres (responsible for control of ventilation) located?
in the pons and medulla
is ventilatory control subconscious or not?
normally subconscious but can be subject to voluntary modulation
what is ventilatory control entirely dependant on? what could be severed to stop breathing from happening?
signalling from the brain, severed spinal cord above origin of phrenic nerve (C3-5) makes breathing stop
what do the respiratory centres do?
set an automatic rhythm of breathing through co-ordinating the firing of smooth and repetitive bursts of action potentials in DRG, adjust this rhythm in response to stimuli
what does DRG stand for? where does it transmit information?
dorsal respiratory group (of neurones), transmits to phrenic and intercostal nerves (inspiratory muscles)
what does PRG stand for?
pontine respiratory group
what does VRG stand for? where does it transmit information?
ventral respiratory group (of neurones), transmits to tongue, pharynx, expiratory muscles
what does NTS stand for?
nucleus tractus solitarius
what modulates respiratory centre rhythm? and via which system?
emotion (via limbic system in the brain), voluntary over-ride (via higher centres in the brain), mechano-sensory input from thorax (e.g: stretch reflex), chemical composition of the blood (PCO2, PO2 and pH) (detected by chemoreceptors)
which of these modulators is the most significant?
chemoreceptor input
which is most superior along the brainstem? pons or medulla?
pons (medulla is just below)
where are central chemoreceptors situated? what do they do?
situated in the medulla, they respond directly to (H+) change is CSF around the brain (which itself directly reflects PCO2), they are the primary ventilatory drive (cause reflex stimulation of ventilation following rise in (H+), reflex inhibition of ventilation if decrease in arterial PCO2 (in case of hyperventilation)
where are peripheral chemoreceptors situated? what do they do?
situated in the carotid and aortic bodies, they respond primarily to plasma (H+) and PO2 (less so to PCO2), they are the secondary ventilatory drive
what are central chemoreceptors driven by?
driven by raised PCO2 (=hypercapnea)
do central chemoreceptors respond directly to (H+) change in the plasma?
no (CSF)
TRUE/FALSE when arterial PCO2 increases, CO2 crosses the blood-brain barrier not H+
TRUE
TRUE/FALSE central chemoreceptors monitor the PCO2 directly in the CSF
FALSE, Indirectly
what two products are formed as a result of increased PCO2?
H+ and bicarbonate
how does ventilation change in response to increased arterial PCO2? decreased arterial PCO2?
increases ventilation, decreases ventilation
what do peripheral chemoreceptors do?
cause reflex stimulation of ventilation following significant fall in arterial PO2 (consider haemoglobin dissociation) or a rise in (H+)
do peripheral chemoreceptors respond to arterial oxygen content?
no, just PO2
is pH falls, ventilation will be stimulated/ inhibited?
stimulated (acidosis)
is pH rises, ventilation will be stimulated/ inhibited?
inhibited (alkalosis)
what does a descending neural pathway from cerebral cortex to respiratory motor neurone allow?
a large degree of voluntary control of breathing
can you override involuntary stimuli such as arterial PCO2 or H+?
well, no of course not it’s “involuntary”
when is ventilation inhibited? what happens chemically speaking?
hyperventilation, during which ventilation is reflexly inhibited by an increase in arterial PO2 or a decrease in arterial PCO2/(H+)
what drugs often result in death as result of respiratory failure if overdosage? what do they do?
barbiturates and opioids depress respiratory centre
what effects do gaseous anaesthetic agents have?
increased respiratory rate but decreased tidal volume so decreased AV (?)
what is nitrous oxide used for? what does it do?
it is a common sedative/ light anaesthetic agent, blunts peripheral chemoreceptor response to falling PaO2
is nitrous oxide safe? when can it cause problems?
for most individuals, yes, it causes problems in patients with chronic lung disease cases (patients often on “hypoxic drive”). Administrating nitrous oxide makes things worse
what happens to respiration during swallowing? why?
it is inhibited to avoid aspiration of food or fluids into the airways
what is swallowing followed by in terms of ventilation? why?
an expiration, to dislodge any particles outwards from the region of the glottis
is the heart entirely dependent on signalling from the brain?
no, but ventilatory control is
what role does stretch reflex have in protecting the respiratory system?
forces expiration to protect alveoli when too much inspiration (reaction to a mechano-sensory input)
what is the blood brain barrier permeable to?
gas
what is the blood brain barrier impermeable to?
ions
