Autonomic Regulation Of The Airways Flashcards
What does the peripheral autonomic nervous system divide into?
Sympathetic and parasympathetic branches, which typically have opposing effects
What does the autonomic nervous system do?
Conveys all outputs from the CNS to the body, except for skeletal muscular control
What are the two types of nerves in the autonomic nervous system?
The pre- and post-ganglionic fibres
The parasympathetic ganglia are near their targets with short post-ganglionic nerves, whereas the sympathetic ganglia are near the spinal cord with longer post-ganglionic fibres
Where is the ganglion in the sympathetic system?
The ganglion is within a chain adjacent to the spinal cord
Where is the ganglion in the parasympathetic system?
The ganglion is within or very close to the effector organ
What happens in parasympathetic bronchoconstriction?
Vagus nerve neurons terminate in the parasympathetic ganglia in the airway wall
Short post-synaptic nerve fibres reach the muscle and release acetylcholine (ACh), which acts on muscarinic receptors of the M3 subtype on the muscle cells
This stimulates airway smooth muscle constriction
What are Antimuscarinics?
Antimuscarinic medications work by blocking muscarinic receptors from the action of acetylcholine, the chief chemical messenger controlling parasympathetic functions.
Blocking the action of acetylcholine can ultimately influence neurologic function, increase heart rate, decrease smooth muscle motility, and decrease exocrine gland secretion.
What are Ipratropium bromide (Atrovent)?
Can be used as inhaled treatment to relax airways in asthma and COPD, but is a short acting antimuscarinic (SAMA)
SAMA less widely used since long acting muscarinic antagonists (LAMAs) were developed
Ipratropium is still used in high dose in nebulisers as part of acute management of severe asthma and COPD
What are LAMAs?
Have long duration of action (many hours), often given once daily (tiotropium)
Increase bronchodilatation and relieve breathlessness in asthma and COPD
Seem to reduce acute attacks (exacerbations) as well
Have other benefits, e.g. on parasympathetic regulation of mucus production
What does the sympathetic nervous system do?
Regulates the fight-and-flight response
What happens in sympathetic regulation?
Nerve fibres release noradrenaline which activates adrenergic receptors, of which there are two main types (alpha/beta)
Nerve fibres in humans mainly innervate the blood vessels, but airway smooth muscle cells have adrenergic receptors (beta)
Activation of beta2 receptors on the airway smooth muscle causes muscle relaxation (by activating adenylate cyclase, raising cyclic AMP)
What are SABAs and LABAs?
Short-acting (salbutamol) and long-acting (formoterol, salmeterol) beta2 agonists are valuable drugs
Given with steroids in asthma, often without steroids in COPD
Often given with LAMA in COPD
Acute rescue of bronchoconstriction
Prevention of bronchoconstriction
Reduction in rates of exacerbations
What are the Adverse effects of β2-agonists?
Raising cAMP may activate Na/K exchange pump driving cellular influx of potassium
Tachycardia (cardiac side effects)
Hyperglycaemia: loss of insulin sensitivity, increased liver glucose release
What are the fundamentals of treatment?
Concordance with therapy is poor
Inhaler education is key
Device selection is vital
What are the goals of treatment?
Most patients have poor control
Aim to improve control
Address important issues for patient (exercise, for example)
Maximum relief of symptoms for minimum side effects
