6. Physiology and pharmacology of airway smooth muscle Flashcards
bronchoconstriction
of Airway smooth muscle
M3
ach
Parasympathetic innervation- vagus
bronchodilation of Airway smooth muscle
β2
Adrenaline
Sympathetic/adrenergic tone
main site of airway resistance
Bronchioles
Reflex activation of bronchoconstriction
Dust
Irritant gases
Smoke
Cold air
Asthma is characterised by
Reversible airways obstruction
Inflammation of airways
Bronchial hyper-reactivity
Relievers of asthma:
β2 adrenoceptor agonists
Methylxanthines
Anticholinergics
Preventers/controllers of asthma:
corticosteroids
anti-inflammatory agents
leukotriene receptor antagonists
Short-acting β2 agonists – physiological antagonists
max effect within 30 min
Duration 3-5 h
muscle tremor at high doses
Longer-acting β2 agonists
8-12 h duration
Theophylline (Methylxanthines)
used as bronchodilator
Acts as a phosphodiesterase inhibitor
Theophylline Therapeutic effects
30-100 µmol/L
Theophylline Unwanted side effects
at 110 µmol/L
dysrhythmias
seizures
tremor
Ipratropium (Antimuscarinic)
bronchodilation
Administered by inhalation
Poorly absorbed
May increase mucociliary clearance
Ipratropium side effects
dry mouth
gastrointestinal motility disorder
Inhaled corticosteroids side effects
adrenal suppression
reduced bone mineral density
Mechanism of corticosteroids
Decrease formation of cytokines
Th2 cytokines reduce activation of eosinophils
IgE production decreases
Leukotrienes and PAF production decreases
β2 receptor expression upregulated
Leukotriene receptor antagonists
Bind to cysLT1
reduces response to: exercise-induced asthma
Given orally (tablets) 1-2 times daily
Side effects include abdominal pain, thirst and headache
Severe Acute Asthma
Status asthmaticus
Medical emergency
Treatment Oxygen (> 60%)
Nebulised salbutamol
IV hydrocortisone
followed by oral prednisolone