Control of Ventilation Flashcards
Requirements of ventilatory control
Stimulation of the (skeletal) muscles of inspiration
Occurs via phrenic (to diaphragm) and intercostal (to external intercostal muscles) nerves
Respiratory centres
Ill defined centres located in the pons and medulla (ventilatory control)
Set an automatic rhythm of breathing through coordinating the firing of smooth and repetitve bursts of action potentials in DRG - travel to inspiratory muscles
Adjust rhythm in response to stimuli
Ventilatory control
Normally subconscious
Can be subject to voluntary modulation
Entirely dependent on signalling from the brain
PRG
Pontine respiratory group of neurons
DRG
Dorsal respiratory group of neurons (resposible for inspiratory muscles)
VRG
Ventral respiratory group of neurons (responsible for tongue, pharynx, larynx and expiratory muscles)
NTS
Nucleus tractus solitarius
Rhythm in respiratory centres modulated by
Emotion (via limbic system in the brain)
Voluntary over-ride (via higher centres in the brain)
Mechano-sensory input from the thorax (eg. stretch reflex)
Chemical composition of the blood - detected by chemoreceptors
Central chemoreceptor
Medulla - responds directly to H+ (directly reflects PCO2). Primary ventilatory drive
Peripheral chemoreceptors
Carotid and aortic bodies - respond primarily to plasma [H+] and PO2 (less so to PCO2). Second ventilatory drive
Not as receptive to falling O2 are as central to rising CO2
Hyperventilation
Ventilation reflexly inhibited by a decrease in arterial PCO2 - negative feedback loops to maintain normal level of PCO2
Fall in plasma pH
[H+] increases - acidosis, ventilation stimulated
CO2 + H2O => H2CO3 <=> HCO3- + H+
Equation driven to left (by blowing off CO2) and lowers [H+] concentration
Rise in plasma pH
[H+] decreases - alkalosis, ventilation inhibited
CO2 + H2O => H2CO3 <=> HCO3- + H+
Equation driven to right (by retaining CO2) and increases [H+] concentration
