Respiratory Physiology - Control of Ventilation Flashcards
Respiratory control system
Negative feedback system
Rhythm controllers in the brainstem:
Medulla oblongata
Dorsal respiratory neuron group - inspiration
Ventral respiratory neuron group - expiration
Pre-Botzinger Complex - pattern generator, also ventral
Rhythm controllers in the brainstem:
Pons
Apneustic centre - excitatory function
Pneumotaxic centre - can inhibit inspiration
Effectors
Respiratory muscles:
1) Diaphragm
2) Intercostal muscles
3) Abdominal muscles
4) Accessory muscles
Sensors
Central chemoreceptors
Peripheral chemoreceptors
Lung receptors
Other receptors
Chemoreceptor definition
Specialised tissue that responds to change in chemical composition of the blood / fluid
Central chemoreceptor
Responds to pH in extracellular fluid (which is similar to CSF pH)
Blood brain barrier prevents certain molecules from diffusing out of blood vessel (eg H+ and HCO3- ions)
More CO2 -> drop in pH -> stimulates central chemoreceptor
pH of CSF
~ 7.32
Buffering of CSF
Low buffering power due to low protein content
Bicarbonate in CSF controlled by choroid plexus
Peripheral chemoreceptor sites
Carotid body - at bifurcation of common carotid artery
Aortic body chemoreceptors (less important than carotid body chemoreceptors)
Also note baroreceptors but they are more relevant for cardiovascular physiology
Carotid body chemoreceptors
Responds to arterial pH, PCO2 and PO2
1/5th of response to drop in pH / rise in CO2 comes from peripheral chemoreceptors (compared with central chemoreceptor)
Type 1 and Type 2 glomus cells
Type 1 glomus cells have high dopamine levels in them
Little response from carotid body in normoxia
Lung receptors
Pulmonary stretch receptors (aka slowly adapting pulmonary stretch receptors)
Irritant receptors (aka rapidly adapting pulmonary stretch receptors)
J receptors (juxta-capillary receptors)
Bronchial C fibres
Hering-Breuer reflex
Seen with pulmonary stretch receptors
As lung is inflated, it will prevent further expansion of the lung
Irritant receptors
Stimulated by irritants eg smoke / smog, cold air
Also some response to stretch
Causes bronchoconstriction
Involved in asthma
J receptors
In alveolar wall close to capillaries
Cause rapid shallow breathing
Eg. with pulmonary oedema, pulmonary fibrosis
Bronchial C fibres
Similar to J receptors but supplied by bronchial vascular system
Other receptors
Nose and upper airway
Joint and muscle
Gamma system
Arterial baroreceptors
Pain and temperature
Gamma system
Involved in sensation of dyspnoea
Response to CO2
Primary factor controlling ventilation
Response to CO2 is reduced during sleep so PCO2 rises slightly whilst asleep
Ventilation response to PO2
PO2 has to drop quite far before notable change in ventilation occurs
No role under normoxic conditions
Response is increased if PCO2 is also raised
Important for high altitude and certain chronic lung disease
Ventilation response to reduced blood pH
Sensed by peripheral chemoreceptors
Important for metabolic acidosis
If severe reduction in pH, central chemoreceptors may be stimulated
Ventilation response to exercise
Ventilation increases but mechanism unclear
In moderate exercise, blood gases remain normal
Types of sleep apnoea
Obstructive
Central
Obstructive sleep apnoea
Airway obstruction from tissue
Sleep deprivation leads to daytime somnolence and cognitive impairment
Central sleep apnoea
Respiratory depression during sleep
Recognised by absence of respiratory efforts
