Physiology 4: Control of Respiration (L6) Flashcards
Name the 2 divisions of respiratory control
- Neural Control
- Chemical Control
Where in the brain is the respiratory centre located
The Pons and Medulla Oblongata
In the brainstem
Name the 3 respiratory groups in the brain
Give their locations
- Pontine respiratory group (Pons)
- Ventral respiratory group (Medulla oblongata)
- Dorsal respiratory group (Medulla oblongata)
Name the 2 parts of the pontine respiratory group
Give their locations
- Pneumotaxic centre (Superior)
- Apneustic centre (Inferior)
What is the general function of the medullary respiratory centres?
To generate rhythm
Describe the Pre-Botzinger complex
- Part of the ventral respiratory group
- Generates breathing rhythm
- Exhibits pacemaker activity (Rhythmic firing)
Describe the dorsal respiratory group
- Stimulated by the Pre-Bötzinger complex
- A medullary respiratory centre
- Fires in bursts to cause contractions of inspiratory muscles
Describe the neural process that leads to inspiration and then expiration
- Pre-Bötzinger complex
generates rhythm - Excites dorsal respiratory group neurons
- Dorsal respiratory group neurons fire as a burst
- Causes the contraction of inspiratory muscles and the pneumotaxic centre to fire
- Pneumotaxic centre inhibits inspiration
- Dorsal firing stops, inspiratory muscles relax
- Passive expiration
What is the consequence of increased dorsal respiratory group neuron firing?
- Excites the ventral respiratory group
- Causing active expiration
Describe the ventral respiratory group
- A medullary respiratory centre
- Excited by the increased firing of dorsal respiratory group neurons
- Activate active expiratory muscles
Do ventral respiratory group neurons activate active expiratory muscles in normal breathing?
No
Only during active expiration
Describe the pneumotaxic centre
- Located in the pontine respiratory group
- Stimulated by dorsal respiratory group neurons
- Its stimulation terminates inspiration
- Prevents apneusis (long inspirations with short expirations)
When the pneumotaxic centre is not functioning what condition is observed
Apneusis
Prolonged inspiration, brief expiration
Describe the apneustic centre
- Located in the pontine respiratory group
- It fires to excite the ventral respiratory group (prolonging inspiration)
- (Apneustic centre wants apneusis)
What is the general function of the pontine respiratory centres?
To modify the rhythm generated by the medulla
Describe the neural process that leads to active expiration
- Pre-Bötzinger complex
generates rhythm - Excites dorsal respiratory group neurons
- Dorsal respiratory group neurons fire more than normal
- Causes the contraction of inspiratory muscles more than normal (and the pneumotaxic centre to fire)
- Pneumotaxic centre inhibits inspiration
- Increased dorsal group firing activates the ventral resp group, activates active expiratory muscles
- Dorsal firing stops –> inspiratory muscles relax
- Active expiration
The respiratory centres are influenced by stimuli received from different places.
List these places
- Higher brain centres (cerebral cortex, hypothalamus)
- Pulmonary stretch receptors
- J receptors
- Temperature
- Adrenaline
- Joint receptors
- Baroreceptors
- Central chemoreceptors
- Peripheral chemoreceptors
Describe the function of pulmonary stretch receptors in the lungs in influencing respiratory centres
- In the walls of bronchi and bronchioles
- Activated by large inspiration
- Activation inhibits inspiration
- The Hering-Breuer inflation reflex prevents hyperinflation
Describe the function of J receptors in the lungs in influencing respiratory centres
- Juxtapulmonary (J) receptors
Stimulated by:
- Pulmonary capillary congestion
- Pulmonary oedema
- Pulmonary emboli
Describe the function of joint receptors in the lungs in influencing respiratory centres
- Stimulated by joint movement (usually in exercise)
NB: (joint receptors ARE NOT J-receptors)
Describe the function of baroreceptors in the lungs in influencing respiratory centres
Decreased bp causes an increased respiratory rate
Describe the Hering-Breuer inflation reflex
- Pulmonary stretch receptors detect excessive inspiration
- Signal to respiratory centres
- Inhibit inspiration
List factors that may increase ventilation during exercise
- Joint receptor stimulation
- Adrenaline release
- Cerebral cortex
- Increase temp (hypothalamus)
- Accumulation of carbon dioxide and hydrogen ions
Describe how a cough is stimulated
- Airway irritation or chemical detection
- Nerve impulse to cough centre in the medulla
- Stimulates a cough
Is chemical control of respiration a negative or positive feedback control system?
-ve feedback control system
Name the 2 types of chemoreceptors
- Peripheral Chemoreceptors
- Central Chemoreceptors
Describe peripheral chemoreceptors
- Found in the carotid bodies and aortic bodies
- Sense the blood gas tensions of oxygen and carbon dioxide
- Senses the [hydrogen ions] in the blood
What are the carotid bodies and aortic bodies?
Carotid:
- Regions of peripheral chemoreceptors in the carotid arteries
Aortic:
- Regions of peripheral chemoreceptors in the aora
Describe central chemoreceptors
- Located near the medullary surface
- Responds to [hydrogen ions] in the cerebrospinal fluid (CSF)
Define blood gas tension
The partial pressure of a gas dissolved in the blood
Give the acronym for the partial pressure of a gas in:
- Arteries, veins, capillaries, alveoli
Artery - a
Alveoli - A
Vein - v
Capillary -c
(include this as subscript between the “P” and The formula of the gas)
The cerebrospinal fluid is separated from blood by what?
- The blood-brain barrier
Describe the permeability of the blood-brain barrier to:
- Hydrogen ions
- Bicarbonate ions
- CO2
Relatively impermeable:
- Hydrogen ions
- Bicarbonate ions
Easily Diffuses:
- CO2
Describe the buffering ability of cerebrospinal fluid
Less than blood
As it has less protein
Describe the effect of arterial hypercapnia on:
- Peripheral chemoreceptors
- Central chemoreceptors
Peripheral Chemoreceptors:
- Weak Stimulation
Central Chemoreceptors:
- Poor buffering in the CSF allows the readily diffused CO2 to generate hydrogen ions
- These H ions dominantly stimulate (dominant control of ventilation)
Describe the effect of arterial hypoxia on:
- Peripheral chemoreceptors
- Central chemoreceptors
Peripheral Chemoreceptors:
- Stimulated if PO2 < 8kPa
- Called the hypoxic drive of respiration
Central Chemoreceptors:
- Severe hypoxia depresses the respiratory centres
Describe when the hypoxic drive of respiration occurs
- Not during normal respiration
- If PO2 falls below 8kPa
- Important if chronic CO2 retention (COPD), or at high altitudes
Define the hypoxic drive of respiration
The stimulation of peripheral chemoreceptors by a low PO2
What are the acute responses to hypoxia?
- Hyperventilation
- Increases cardiac output
What are the chronic responses to hypoxia?
Describe the purpose of these changes
- Red blood cell production (better oxygen carrying capacity)
- Increased 2,3-bisphosphoglycerate in RBCs (oxygen offloaded more readily at tissue)
- More capillaries (better difusion)
- More mitochondria (more efficient oxygen use)
- Kidneys conserve acid (arterial pH decrease)
Describe the effect of arterial H ions on:
- Peripheral chemoreceptors
- Central chemoreceptors
Peripheral Chemoreceptors:
- Stimulation (important in acid-base balance)
Central Chemoreceptors:
- No effect (H ions can’t cross the blood brain barrier)
