Respiratory 5 Flashcards
Ventilation is subject gl modulation and control by…
CNS
Chemical factors
Peripheral factors
What are the sensors of the respiratory system?
Chemoreceptors(central and peripheral)
Mechanoreceptors(joint, muscle and pulmonary receptors)
What are the effectors of the respiratory system?
Respiratory muscles-diaphragm, intercostals, abdominal muscles
What are the parts of the respiratory control center?
Pons and medulla
What controls voluntary control of the respiratory system?
Cerebrum
What parameters are monitored in the respiratory system?
PCO2
- pH
- PO2
- Stretch
- Irritation
What are the neural control centers of the respiratory system?
Cerebrum- voluntary control
Medulla oblangata- basic rhythmic pattern of breathing
- Dorsal Respiratory Group(DRG)
- Ventral Respiratoru Group(VRG)
- Central Pattern Generator
Pons
- Pneumonic center
- Apneuistic center
Emotional centers- anxiety, fear, rage
- Hypothalamus
- Limbuc system
Describe Dorsal Respiratory Group(DRG)
- Inspiratory (I) neurons
- Inspiratory center
- Motor neuron control of diaphragm and external intercostal muscles
- Maintains a constant breathing rhythm
- Functions mainly in quiet inspiration
- When DRG activity ceases- expiration occurs
- Input is from the vagus and glossopharyngeal nerves and output is via phrenology nerves
Describe the ventral respiratory Group (DRG)
Intense inspiration (I+) neurons Expiration (E) neurons
- Functions mainly in forced breathing
- Activate expiratory and inspiratory centers
- Motir neuron control of accessory respiratory muscles
Describe Central Pattern Generator
- Pre-Botzinger complex-contained within the DRG and VRG complex
- Pacemaker- like activity seen in experiments, exact description is uncertain
- Injury abolishes rhythmic breathing
Describe VRG & DRG activity
Pattern of activity the DRG & VRG neurons is “ramp-like” I.e. Action potential frequency increases gradually till it reaches a crescendo
What is the Pneumonic center?
- Upper pons
- Decreases the depth and duration if inspiration
- Possibly involved in regulation of inspiratory volume and therefore respiratory rate
Describe the apneustic center
- Lower pons
- Sends signals to prevent switching off of inspiration
- Increases the depth and duration of inspiration
What are the typ3s of chemoreceptors?
Central and peripheral
Where are central chemoreceptors located?
In the ventral surface of the medulla
What are the effects of the central chemoreceptors ?
Responds to a change in PaCO2 and pH of the Cerebrospinal fluid(CSF)
- CSF is separated from the blood by the blood brain barrier which is largely impermeable to H+ and HCO3-
- Therefore metabolic acidosis or alkalosis has relatively little effect of CSF pH
- The blood brain barrier is very permeable to O2 to. CO2
- PCO2 has a strong effect on CSF pH and is therefore a powerful stimulus for ventilation
What is the most important chemical controller of ventilation?
Carbon dioxide
If CSF CO2 levels are high if blood CO2 levels are high
Results in increased breathing rate and ventilation
Where are peripheral chemoreceptors located?
In the carotid and aortic bodies
Describe peripheral carotid bodies
Detect changes in PaCO2, PaO2 and pH
Carotid body
- Small (2 mm) sensory organ
- Bifurcation of the carotid artery
- Afferents feed CNS via theglossopharyngeal nerves
Aortic body
-Multiple bodies along aorta- afferents feed CNS via vagus nerve
Glomus cells- site of chemoreception
What is the Glomulusvcell response to increased PCO2 & H+?
Increased PaCO2
Causes acidification which also causes depolarization
-Increased ventilatory drive
Increased H+
Causes acid loading into cell-depolarization
-Increased ventilatory drive
What is the Glomus cell response to hypoxia?
Decreased PaO2
-depolarizes glomus cell stimulates afferents to the CNS
-Increased ventilatory drive
What are the respiratory reflex pathways?
- Pulmonary stretch pathways
- Irritant receptors
- J receptors
- Proprioceptors
Describe the action of stretch recept9rs
Lie in the smooth muscle layer of the airways
Fire in the proportionate response to extent of inflation
-Pulmonary stretch associated with lung inflation terminate inspiration in a reflex that prevents over inflation of the lung -Hering Breuer reflex
Describe the action of the muscle and joint receptors
Located in th3 chest wall
Sense chest wall movement and the effort involved in breathing
-Stimulates increased force of inspiration and expiration
Limb joints have similar effects during exercise
Describe the action of irritant receptors
Located in the epithelium of large conducting airways
- Senses, dust, chemicals, smoke, ammonia, cold air
- Effect is to stimulate bronchoconstriction, mucus secretion and coughing
- Protects the respiratory zone
Describe the juxtapulmonary capillary receptors
- J receptors, located in alveolar walls
- Unmyelinated nerve fibers(C fibers)
- Senses chemicals, stretch, pulmonary edema
- Causes bronchoconstriction, mucus secretion and shallow breathing
Describe the integrated ventilatory response
Changes in PaCO2, pH, and PaO2 rarely occur in isolation
- Changes in activity and the environment initiate the integrated ventilatory response that involve changes in the cardiopulmonary system
- Respiratiry center is forced to make choices about an appropriate ventilatory response
- Generally output from the respiratory center is designed to optimize PaCO2 but, changes in the other parameters influence system sensitivity
How do chemoreceptors respond to the integrated response?
- Carotid response: detect increased PaCO2 but only increase ventilation slightly (20%) ; immediate response
- Central chemoreceptors detect PaCO2 and dominates the ventilatory response within minutes
- PaCO2 of arterial blood is an extremely potent ventilatory stimulus
Modest changes in PaO2 has little effect on ventilation (must be below 60 mm Hg)
-The response to PaCO2 is potentiated by low PaO2
What are the responses of the integrated response?
- Increased ventilation—> PaO2 increases and PaCO2 falls
- Respiratory control centers seek to optimize PaCO2
- Mild hypoxia is overridden to stabilize CO2
- Comditions that decrease PaO2 usually result in increased PaCO2 and lowered pH
What is the clinical correlation of PaCO2?
In some chronic diseases, where PaCO2 is high but pH compensated, the hypoxia drive becomes more important (since the PCO2 response is largely due to change in pH)
-Example: In patients with an acute exacerbation of COPD, administering O2 may help normalize PaO2 but can suppress respiration
A titrated oxygen therapy has to be done for these patients
Explain the control of respiration at low oxygen tensions: high altitude
- Decreased barometric pressure
- Decreased PIO2
- Decreased PAO2(hypoxia)
- Decreased PaO2(hypoxemia)
- Increased chemoreceptor activity, pulmonary vasoconstriction
- Hyperventilation, increased cardiac output
- In hours to days—> increased PAO2 and PaO2, decreased PACO2(hypocapnia & respiratory alkalos8s)
- Increased 2,3 DPG
- Months to years- increased erythropoietin, angiogenesis, ventricular remodeling
Explain the control of respiration during exercise
- Mild to moderate exercise- increased oxygen consumption and CO2 production - stretching of muscles and tendons
- Increased ventilation, increased CO2 removal
- Unchanged arterial pH
- Increased intensity-lactic acid formation, further increase in ventilation, increased cardiac output
- Metabolic acidosis ensues, tidal volume continues to increase until it is limited or exhaustion. Occurs
