regulation of respiration, mmmp
TRANSCRIPT
Dr. Nisreen Abo-elmaaty
Regulation of Respiration
Dr. Nisreen Abo-elmaaty
The Respiratory system in human performs a critical task
That is to regulate & respond to O2
demands Maintaining a constant O2 & CO2 in the
blood Therefore, regulation of respiration is
critically important for Homeostasis
Dr. Nisreen Abo-elmaaty
Integrator (Centre) → neural network in brainstem Sensors → The main are chemosensors
sensing changes in CO2, O2 & pH
Other contributors: in the lungs, cardiovascular, skeletal muscles, tendons of respiratory muscles,
Effector → respiratory muscles
Inspiration; diaphragm &external intercostals Expiration; internal intercostals & abdominal recti
The Respiratory Control System
Dr. Nisreen Abo-elmaaty
The Respiratory Centre
• Present in brain stem
• Medullary group of neurons (rhythmicty centre)
• Pontine: Apneustic Pnemotaxic
Dr. Nisreen Abo-elmaaty
Medullary Respiratory Neurons(Rhythmicity Centre)
2 distinct groups of neurons; The Dorsal Inspiratory Group (DIG) The Ventral Expiratory Group (VEG)• The 2 groups are bilaterally paired• There is cross communication between them responsible for initiation & regulation of
breathing
Dr. Nisreen Abo-elmaaty
• Inspiratory neurons that discharge during inspiration & stop discharging during expiration (Respiratory Rhythm generator)
• They generate a Ramp Signal;
they initiate inspiration with a weak burst of action potentials that gradually increase in amplitude, then ceases for the next 3 sec. until a new cycle begins
• This provides a gradual increase in lung volume during inspiration
Medullary Respiratory NeuronsDorsal Respiratory Group (DRG)
Dr. Nisreen Abo-elmaaty
Medullary Respiratory NeuronsInput & Output of DRG
DRG
Central chemoreceptors
Peripheral chemoreceptors
Pneumotaxic centreApneustic centre
-+
+
Spinal motoneurons
Cervical (3,4,5) & Thoracic (1-12)
Dr. Nisreen Abo-elmaaty
Medullary Respiratory NeuronsVentral Respiratory Group (VRG)
• Anterolateral to DRG• Activated during heavy breathing; e.g.
exercise • During such conditions, the increased activity
of inspiratory neurons activates the VRG• In turn, the activated VRG discharge: - inhibits inspiratory group - stimulates the muscles of expiration; internal
intercostals (T6-L3), abdominal recti (T4-L3)
Dr. Nisreen Abo-elmaaty
Pontine Respiratory Centre
2 pontine centres that modify
The rate & The Pattern of respiration
Dr. Nisreen Abo-elmaaty
Pontine Respiratory Centres
Apneustic centre:• In the lower 1/3 close to
medullary groups• sends stimulatory
discharge to inspiratory neurons promoting inspiration
• Removal of its stimulatory effect→ respiration becomes shallow & irregular
Dr. Nisreen Abo-elmaaty
Pontine Respiratory Centres
Pneumotaxic centre• In upper 2/3 of pons• Its major role is regulation of
respiratory volume & rate• Controlling cessation of
inspiratory ramp signal from DIG;
• Switch-off DIG & apneustic centre → expiration occurs
• Hypoactivation of this centre →prolonged deep inspiration with limited brief expiration
• Hyperactivation →shallow inspiration
Dr. Nisreen Abo-elmaaty
How Pontine Respiratory Centres work to regulate rhythmic respiratory cycle?
Active dorsal medullary inspiratory neurones→ stimulatory discharge to ms. Of inspiration & pneumotaxic centre → activated pneumotaxic centre inhibits apneustic & DRG → initiation of expiration
• Then, the spontaneous activity of inspiratory neurons starts another cycle
Dr. Nisreen Abo-elmaaty
The co-ordinated work of neurons of respiratory centre
+
Dr. Nisreen Abo-elmaaty
Overall Control of Activity of Respiratory Centre
A). Involuntary (Automatic) Control: I- Chemoreceptor Reflexes II- Neurogenic Reflexes B). Voluntary Control
Dr. Nisreen Abo-elmaaty
A). Involuntary Automatic ControlI- Chemoreceptor Reflexes
Chemical regulation of activity of Respiratory centre which involves 2 pathways:
1- Central Chemoreceptor Pathway
2- Peripheral (Arterial) Chemoreceptor Pathway
These chemoreceptors sense changes in PaCO2, PaO2 & pH
Dr. Nisreen Abo-elmaaty
1- Central Chemoreceptors Pathway Its receptors: Central chemosensitive area• Lying just beneath
ventral surface of medulla
• Relaying most important sensory input about changes in their close environment to respiratory centre in medulla & pons
• Most sensitive to change in PaCO2 ,H+ conc., but not to PaO2
Dr. Nisreen Abo-elmaaty
• Under normal conditions, ~75-85% of respiratory drive is due to stimulation of central chemoreceptors by PaCO2
• However, the direct stimulant for neurons of central chemoreceptors is only H+ ions
• But H+ can not cross blood brain barrier while CO2 can
• So, how central chemoreceptors are stimulated by an increase in arterial PCO2?
1- Central Chemoreceptors Pathway Central chemosensitive area
Dr. Nisreen Abo-elmaaty
More sensitive to changes in CSF than to changes in cerebral blood
Dr. Nisreen Abo-elmaaty
2- Peripheral Chemoreceptor PathwayPeripheral (Arterial) Chemoreceptors
Peripheral chemoreceptors are the only sensors detecting a fall in PO2
Dr. Nisreen Abo-elmaaty
2- Peripheral Chemoreceptor Pathway Stimulation of Peripheral chemoreceptors
• The carotid & aortic bodies are sensitive to
fall in PaO2, an increase in PaCO2 or H+
concentration• They maximally stimulated when
PaO2 decreases below 50-60mm Hg• They detect changes in dissolved O2
but not in the O2 that is bound to Hb (e.g. in anaemia there is normal PaO2 but reduced content of O2 bound to Hb)
Dr. Nisreen Abo-elmaaty
What if Carotid bodies are removed?
• if there is decreased PaO2 (Hypoxia) with absence of peripheral chemoreceptors Hypoxia would inhibit respiration
Why?• hypoxia depresses neuronal activity
including that of respiratory centre• Hypoxia →VD of cerebral vessels
→↓PaCO2 in CSF →↓CO2-mediated stimulation of central chemoreceptors → hypoventilation
Dr. Nisreen Abo-elmaaty
A). Involuntary Automatic ControlII- Neurogenic Reflexes
Hering-Breuer Inflation Reflex Hering-Breuer Deflation Reflex J-receptor Reflex Cough & sneezing Reflexes Baroreceptors Reflex Other influences (mediated via
hypothalamus)
Dr. Nisreen Abo-elmaaty
Neurogenic Reflexes originating from the respiratory system1- Hering-Breuer inflation reflex (inhibito-inspiratory reflex)
• Over-Inflation of lungs→ stimulation of slowly adapting stretch receptors in smooth muscles of large & small airways →afferent vagal signals → inhibitory to medullary and pontine inspiratory network →termination of inspiration
• This reflex in not important in normal adults. It is more important & powerful in neonates.
Dr. Nisreen Abo-elmaaty
Neurogenic Reflexes originating from the respiratory system 2- Hering-Breuer deflation reflex (excito-inspiratory reflex)
• Deep expiration → Deflation of the lungs → ↓activity of previous slowly adapting stretch receptors or stimulate other propioceptors in respiratory muscle → decreasing afferent vagal signals to respiratory centres→ increase in the activity of inspiratory neurons →↑ rate of breathing
Dr. Nisreen Abo-elmaaty
Neurogenic Reflexes originating from the respiratory system 3- J-receptor Reflex
• Pulmonary emboli or oedema or congestion → stimulation of juxtapulmonary-capillaries receptors →impulses along vagal afferent → respiratory centre → rapid shallow breathing
• These receptors are responsible for the sensation of air hunger (Dyspnea; shortness of breath)
Dr. Nisreen Abo-elmaaty
Neurogenic Reflexes originating from the respiratory system 4- Cough, Sneezing reflexes
• Dust, smoking, irritant substances → stimulation of irritant receptors in upper airways (nose, larynx, bronchi)→afferent signals via vagus (larynx, cough}) or trigeminal or olfactory (nose, sneezing) → respiratory centre → deep inspiration followed by forced expiration against closed glottis →opening of glottis →forceful outflow of air (help removal of irritants)
Dr. Nisreen Abo-elmaaty
Neurogenic Reflexes from other systems Baroreceptor Reflex
• Acute ↑in ABP → stimulation of baroreceptors →afferent signals via X & IX → inhibitory to respiratory centre → decrease rate & depth of respiration → ↓venous return → ↓COP → ↓ABP
Dr. Nisreen Abo-elmaaty
Dr. Nisreen Abo-elmaaty
Neurogenic Reflexes Other Influences from higher centershypothalamus & limbic system
• Temperature: Increases respiratory rate• Pain: Sudden pain decreases, prolonged
pain increases rate• Alcohol: Decreases rate• Exercise; increases breathing rate (higher
cortical centers)
Dr. Nisreen Abo-elmaaty
• Through descending tracts from the cerebral cortex to motor neurons of the respiratory muscles (dorsolateral corticospinal tracts)
• This provides CNS the ability to override the automatic regulation of respiration for short time e.g. holding breath but the involuntary control will take over (↑ PCO2, H+), or deliberate hyperventilation (↓PCO2)
B). Voluntary Control of BreathingCortical Influence
Dr. Nisreen Abo-elmaaty
Now, can U explain what u have read about Luke?• His respiratory rate of 22/min• His PaO2 was 61 mm Hg• His PaCO2 was 31 mm Hg
Dr. Nisreen Abo-elmaaty
Summary in Figures
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The Effect of ↑ PaCO2 on ventilation
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Effect of a decreased PaO2
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Summary of Chemical Pathways stimulating Ventilation
Dr. Nisreen Abo-elmaaty
Summary Of the Overall Control of Activity of Respiratory Centre
Dr. Nisreen Abo-elmaaty
Now, You should ask yourself if you know the followings:
• General organization of respiratory control system• Localization & description of brain stem centres
involved in regulation of breathing• The sensors that sense changes in PaO2, PaCO2 & H+
• The effects of changes in PaO2, PaCO2 & H+ on breathing
• The list of reflexes that affect the breathing pattern
Dr. Nisreen Abo-elmaaty
Dr. Nisreen Abo-elmaaty
Mark the following T or FRespiratory chemoreceptors:
a). in the carotid and aortic bodies are most important in the ventilatory response to an elevated PCO2 b. in the carotid and aortic bodies are strongly stimulated by the low arterial O2 content in anaemic patients c). in the medulla are responsive to changes in arterial PCO2 d. transducer a chemical changes into electric signals e. may be sensitive to H+
Dr. Nisreen Abo-elmaaty
Choose the best answer
– Voluntary apnea for 90 seconds will
a. Increase arterial PCO2
b. Decrease arterial PO2
c. Stimulate the arterial chemoreceptors
d. Stimulate the central chemoreceptors
e. All of the above
Dr. Nisreen Abo-elmaaty
• What is the function of the Apneustic centre in the brain?
a) monitor changes in CO2, O2 & H+ ions
b) sends inhibitory signals to Inspiratory area in medulla
c) sends stimulatory signals to Inspiratory area in medulla
d) monitors changes in blood pressure
Dr. Nisreen Abo-elmaaty
– Stimulation of which of the following receptors should result in decreased ventilation?
a. Aortic chemoreceptors
b. Carotid chemoreceptors
c. Central chemoreceptors
d. Hering-Breuer inflation (stretch) receptors
Dr. Nisreen Abo-elmaaty
THANK U