Control of Ventilation Flashcards
Where in the body is ventilation controlled?
- Respiratory centre
- Brain stem: pons and medulla
Is arterial blood PO2 and PCO2 ever altered?
- No (rarely)
- Since nervous system adjusts the rate of alveolar ventilation
What are respiratory sensors?
- Chemoreceptors
- Lung receptors
- Other receptors
What are respiratory effectors?
- Respiratory muscles
What does the medullary respiratory group consist of?
- Dorsal respiratory group
- Ventral respiratory group
What is the function of the dorsal respiratory group?
- Inspiratory neurons
- Fire signals inducing muscle contraction → inspiration
external intercostals + diaphgram
What is the function of the ventral respiratory group?
- Both inspiratory and expiratory neurons
- Remain inactive during quiet breathing
- Used when demand of ventilation is increased (active expiration)
What kind of breathing rhythms does the medulla generate?
pacemaker like activity
- normal breathing (fast, low amplitude)
- sighs (slow, large)
What does the Pons respiratory group consist of?
- Pneumotaxic center
- Apneustic center
What do the pneumotaxic group do?
- Inhibits inspiratory neurons
- sends signal to DRG
- prevents over-inflation of lungs
What does the apneustic group do?
- Prevents inspiratory neurons from being switched off
- Stimulates DRG and VRG
What is the neuronal oscillatory circuit?
- Inspiratory circuit fires for 2 seconds
- Inspiratory circuit dormant for 3 seconds (expiration occurs)
expiratory circuit activated during exercise
What are strong and weak breathing impulses?
- Strong: 0.5s inspiration
- Weak 5-7s inspiration
What is the Hering-Breur Reflex?
- Stretch receptors in lung tissue, bronchi, bronchioles
- transmit inhibitory signals via vagus nerve (X) to inspiratory area; prevents over inflation go lungs
What does an impaired respiratory circuit cause?
- Hypoventilation + hypoxemia
What inputs lead to the respiratory centres?
Airways and lungs: (all via vagus nerve)
- Stretch receptors
- Irritant receptors
- J receptors
Chemoreceptors:
- Peripheral
- Central
What are irritant receptors?
- Near epithelial airway cells
- stimulated by gases, cigarette smoke, dust
- travel by vagus nerve
- cough reflex, bronchoconstriction
What are J receptors?
- near capillaries in alveoli walls
- stimulated by pulmonary congestion and oedema
- travel via vagus nerve
- cause rapid shallow breathing
What is the function of peripheral chemoreceptors?
- Located near heart in carotid and aortic bodies
- via vagus and glossopharyngeal nerve to DRG
- Stimulated by decrease in PaO2 and increase in PaCO2 and H+
- Increases breathing
a = arterial
What is the function of central chemoreceptors?
- Located in medulla
- stimulated by increase in brain ECF PCO2 and H+
- Responsible for 80% of ventilatory repsonse to increase PaCO2
- poor response to arterial H+ = BBB
a = arterial
What is the ventilatory response to hypoxia?
- not so sensitive
- response increases after PaO2 is < 60 mmHg
What is the respiratory response to hypercapnia?
- very sensitive
- increased ventilatory response even with small changes in PaCO2
- causes increased neuromuscular excitability, tetany, coma
What is considered Hypoxic?
- PaO2 < normal
What is considered anaemic?
- PaO2 normal
- O2 content < normal
What is Stagnant?
- PaO2 + O2 content normal
- decreased blood flow
What is Histotoxic?
- PaO2, O2 and delivery all normal
- metabolic poisoning, so tissue cannot use O2 (cyanide)
What disorders do you get with decreased ventilation?
- Neurological damage, muscular disorders, obstructive + restrictive diseases
What diseases do you get with decreased alveolarcapillary diffusion?
- Emphysema
- Oedema
- Fibrosis
- Atelectasis
What diseases do you get with decreased pulmonary transport?
- anemia
- CO poisoning
What is the difference between hypoxia and hypoxaemia?
- Hypoxia: decreased PO2 in tissues
- Hypoxaemia: PO2 less than normal in BLOOD
