Control of Respiration Flashcards
Which neural centres control respiration?
Medulla oblongata mainly but the pons has a role
Where is breathing rhythm generated?
Pre Botzinger complex. These nerves display pacemaker activity
How is inspiration initiated?
Rhythm is generated by the pre Botzinger complex which excites the dorsal respiratory group of neurones which fire leading to contraction of inspiratory muscles
What happens during hyperventilation neurologically?
Increased firing of the dorsal respiratory group excites the ventral respiratory group of neurones which leads to the contraction of internal intercostal muscles and abdominal muscles => forceful expiration
How can the rhythm generated in the medulla be modified by the pons?
Stimulation of the pneumotaxic centre will terminate inspiration.
Stimulation of the apneustic centre will prolong inspiration.
When is the pneumotaxic centre stimulated?
When the dorsal respiratory neurons fire.
What results from a faulty pneumotaxic centre?
Prolonged inspiratory gasps with little expiration. Apneusis
What will influence the respiratory centre?
Higher brain centres (cerebral cortex, limbic system, hypothalamus)
Stretch receptors (in the walls of bronchi and bronchioles)
Juxtapulmonary receptors (stimulated by pulmonary capillary congestion and pulmonary oedema)
Joint receptors
Barroreceptors (decreased BP => increased ventelation rate)
Chemoreceptors (peripheral and central detecting blood gas levels)
What causes congestion in pulmonary capillaries?
Left ventricular failure and pulmonary emboli
What is the Hering-Breur reflex?
A reflex of the stretch receptors in the lungs which prevents hyperinflation (more important in children)
Give factors which increase ventilation during exercise.
Pulmonary stretch receptor activation Joint receptor activation Adrenaline release Increase in body temperature Generation of carbon dioxide and H+ ions Impulses from cerebral cortex
Explain how the cough reflex works?
Afferent discharge stimulates a short intake of breath followed by closure of the larynx, then contraction of the abdominal muscles and finally open of the larynx and expulsion at high speed.
Why do we have a cough reflex and what stimulates it?
It helps to clear airways of dust, dirt or excessive secretions. It is activated by irritation in the airways or tight airways
What do peripheral chemoreceptors sense and where are they found?
Oxygen mainly, but also carbon dioxide and H+.
Found in the carotid and aortic bodies
What do central chemoreceptors sense and where are they found?
Respond to the H+ ion concentration in the cerebrospinal fluid.
Found near the surface of the medulla in the brain stem
How is cerebrospinal fluid separated form the blood?
Blood brain barrier
What is the blood brain barrier permeable to?
Permeable to carbon dioxide but relatively impermeable to H+ and HCO3-
How is hypercapnia detected?
If carbon dioxide in the blood is high it will diffuse into the cerebrospinal fluid. This will cause an increase in H+ ions leading to increased ventilation.
How is Hypoxia detected?
Peripheral chemoreceptors are stimulated if PaO2 falls below 8kPa => increased ventilation.
If PaO2 becomes very low then neurones will be depressed => decreased ventilation
When is hypoxic drive important?
In chronic carbon dioxide retention. COPD
At high altitudes
What are the chronic adaptions to high altitude hypoxia?
Increased RBC production
Increased number of capillaries
Increased number of mitochondria
Kidneys conserve acid
How is ventilation effected by the H+ drive?
Detected by peripheral chemoreceptors. They help to adjest for acidosis caused by the non carbonic acid H+ ions to the blood
Normally lactic acid or diabetic ketoacidosis.
Stimulation => hyperventilation and increased elimination of carbon dioxide
