Week 10 - Control of respiration Flashcards
What is homeostasis?
The state of steady internal, chemical and physical conditions maintained by living systems
What does ventilatory control involve?
Sensors
Afferent pathway
Respiratory control centre
Efferent nerve fibres
Spinal cord
Effectors
What are the sensors in the ventilatory control centre and what do they do?
Peripheral chemoreceptors
Central chemoreceptors
Pulmonary mechanoreceptors
They detect change and things that need to be altered e.g. too much hyperventilation or hypoventilation, increase in CO2 or decrease in O2.
What does the respiratory control centre consist of?
Medulla, pons
What do the effectors in the ventilatory control centre consist of?
Respiratory muscles
Diaphragm
What are chemoreceptors? (2 types)
Cell that responds to chemical compounds to give an impulse to a sensory nerve.
2 sets:
↳ Oxygen receptors which are in peripheral nervous system
↳ Carbon dioxide receptors which are found both peripherally and centrally
What are mechanoreceptors?
Sensory receptors that respond to mechanical deformation of the receptor or surround tissue
What are stretch receptors?
Respond to the stretching of muscles by giving impulses to the CNS
What are proprioceptors?
Cells that monitor body changes brought about by muscular movement to give an impulse to the CNS to co-ordinate movement
What are juxtacapillary receptors?
Cells that cause an increase in breathing rate as reflex response, thought to be involved in the sensation of dyspnea.
What are nociceptors?
Cells that respond to a pain stimulus by giving impulses to the central nervous system
Where are the medulla and pons found in the brain?
in the brain stem
Definition of “nuclei” in neuroanatomy?
- Nucleus is a collection of neuronal cell bodies within the CNS
- The neurons in one nucleus usually have roughly similar connections + functions
- Nuclei are connected to other nuclei by tracts, the bundles (fascicles) of axons (nerve fibres) extending from the cell bodies
What do chemoreceptors do?
Monitor blood gas tensions, PaCO2, PaO2 and pH, and help keep minute volume appropriate to the metabolic demands of the body.
Therefore, chemoreceptors respond to:
↳ hypercapnia (CO2 too high)
↳ hypoxia (O2 too low)
↳ acidosis (low pH)
The most important factor controlling the rate and depth of breathing is the effect of carbon dioxide on the central chemoreceptors.
What are the respiratory control centres?
Areas of the brain and spinal cord involved in control of breathing
What are the 4 respiratory control centres?
Pneumotaxic centre
Apneustic centre
Dorsal respiratory group (inspiratory)
Ventral respiratory group (expiratory)
Where is the pneumotaxic centre located?
upper aspect of pons
What is the function of the pneumotaxic centre?
→ Controls fine tuning of respiratory rate and depth
→ Sends signals inferiorly and can influence VRG and DRG
→ Inhibits inspiration, which allows for transition from inspiration to expiration
→ Decreases tidal volume
Transitioning occurs as a response to stimulus from peripheral receptors.
Where is the apneustic centre located?
lower aspect of pons
What is apeneusis?
Prolonged breathing
What is the function of the apneustic centre?
→ Controls prolonged breathing
→ Receives peripheral stimulus from stretch receptors
→ Sends signals to the VRG + DRG to trigger inspiration
→ Increased tidal volume
What would occur if the pneumotaxic centre is damaged?
- DRG + VRG would only receive signals from apeneustic centre.
- It cannot inhibit transition from inspiration to expiration and undergoes prolonged inspiration.
- Also known as apneustic breathing.
Where is the dorsal respiratory group located?
Located medially in aspect within the medulla
What is the function of the dorsal respiratory group?
→ Receives peripheral stimulus signals from the stretch receptors, proprioceptors, juxtacapillary receptors, and both central and peripheral chemoreceptors.
→ Sends signals to external intercostals and diaphragm to cause inspiration.
Where is the ventral respiratory group located?
Anterior aspect of the medulla
What is the function of the ventral respiratory group?
→ Controls expiration via sending expiratory signals
- VRG - stimulates expiratory movements
- DRG - stimulates inspiratory movements
Key points about central chemoreceptors?
→ 80% of drive for ventilation as a result of their stimulation
→ When inactivated, respiration ceases
→ Readily depressed by drugs
Location of central chemoreceptors?
- In the brainstem on the ventrolateral surface of the medulla.
- Anatomically separate from medullary respiratory control centre.
What are central chemoreceptors sensitive to?
- Respond to hydrogen ion concentration within surrounding brain tissue and cerebrospinal fluid as well as low partial pressure of O2.
→ Raised hydrogen ion conc. = increased ventilation
→ Lowered hydrogen ion conc. = decreased ventilation
What is the function of the central chemoreceptors? (how do they achieve homeostasis)
→ Increase in pCO2 levels leads to increased carbonic acid in CSF
→ Leads to increase in protons in CSF
→ Central chemoreceptors are stimulated, leads to increased ventilation and increase in blood pH (bringing it back to a normal level)
Key points about peripheral chemoreceptors?
Stimulation of peripheral chemoreceptors has both cardiovascular and respiratory effects.
Cartoid bodies have a greater influence on respiration.
Where are peripheral chemoreceptors located?
Around carotoid sinus and aortic arch
What are the peripheral receptors sensitive to?
PaO2
PaCO2
pH
Blood flow
Temperature
What do the carotid bodies do?
(2 types = type i , type ii)
→ Rich blood supply to the carotid bodies - (blood flow per mass of tissue far exceeds that to the brain) - venous blood flow, therefore remains saturated with oxygen.
→ Believed that type i (glomus) cells are activated by hypoxia and release transmitter substances that stimulate afferents to the brainstem
Stimuli that increase breathing rate and depth?
- Voluntary hyperventilation controlled by cerebral cortex and anticipation of activity by stimulation of limbic system
- Increase in arterial blood pCO2 above 40mmHg (causes increase in H+) detected by peripheral and central chemoreceptors.
- Decrease in arterial blood pO2 from 105mmHg to 50mmHg
- Increased activity of proprioceptors
- Increase in body temp.
- Prolonged pain
- Decrease in blood pressure
- Stretching of anal sphincter
Stimuli that decrease breathing rate and depth?
- Voluntary hypoventilation controlled by cerebral cortex
- Decrease in arterial blood pCO2 below 40mmHg (causes a decrease in H+) detected by peripheral and central chemoreceptors.
- Decrease in arterial blood pCO2, below 50 mmHg
- Decreased activity of proprioceptors
- Decrease in body temp. , sudden cold stimulus
- Severe pain (causes apnea)
- Increased blood pressure
- Irritation of pharynx or larynx by touch or chemicals (brief apnea followed by coughing/sneezing)
What is apnea?
breathing repeatedly stops and starts
