Asthma Flashcards
Explain the pathophysiology of asthma
1) On exposure to an allergen, the antigen is engulfed by an APC in the bronchial epithelium
2) The allergen is presented by the APC cells to TH0 cells which are then converted into TH2 cells in response to allergen presence
3) TH2 stimulates B cells via IL-4 and IL-13 secretion to facilitate the class switch from IgM to IgE of plasma cells
4) IgE produced by the plasma cells binds to mast cell receptors via Fc complex
5) Binding of the allergen to the mast cell IgE causes mast cell degranulation and eosinophil action which leads to the production of histamine, protease and mucus
Outline the action of histamine
Histamine binds to H1 receptors in the smooth muscle in order to stimulate the parasympathetic nervous system which leads to bronchoconstriction, as well as increasing vascular permeability and causing systemic vasodilation
What are other causes of wheeze that are not associated with asthma?
Bronchiolitis in children, upper airway obstruction, stridor (harsh or grating sound), upper airway dysfunction and COPD
How is asthma diagnosed?
During an asthma attack, all indicators of expiratory flow are reduced (as it’s an obstructive disorder), but after the use of bronchodilators these indicators will increase
Why may exercise exacerbate asthma?
Exercise increases ventilation rate which causes cooling of the airways which can induce bronchospasm (spontaneous airway restriction due to beta 2 inhibition)
How can smoking cause asthma to worsen?
Smoking causes oxidative stress by increasing NFkB levels and by blocking the steroid response by HDAC2 (therefore inflammation cannot be inhibited)
Why is it important to treat asthma?
Poor control of asthma will lead to long-term airway changes (remodelling) which can lead to COPD
What are theophyllines and how may they be used int he treatment of asthma?
They are leukotriene antagonists and have general effects to reduce inflammation, increase heart rate, increase blood pressure and relax bronchial smooth muscle
Outline the mechanism of action of salbutamol
It is a short-acting beta 2 adrenoreceptor agonist; beta 2 receptors are found in the smooth muscle of airways and activation causes relaxation of smooth muscle in order to cause bronchodilator
Outline the mechanism of action of leukotrienes in the treatment of asthma
Leukotrienes increase vascular permeability and cause systemic vasodilation and therefore antagonism will raise blood pressure to increase blood supply and prevent further inflammation of the bronchial wall in order to increase bronchial lumen diameter
What does a normal or elevated pCO2 level indicate in someone experiencing an acute asthma exacerbation?
THIS IS A SIGN OF RESPIRATORY FAILURE! The individual’s lungs have become exhausted and are due to go into complete respiratory arrest which is fatal
