4.9 Anaphylaxis Flashcards
What type of cell causes anaphylactic symptoms?
Mast cells
What binds to mast cells?
IgE
What are the main signalling molecules involved in anaphylaxis?
Histamines and leukotrienes
What do histamines act on?
Blood vessels and smooth muscle
What affect does histamine have in connective tissue?
Vasodilation with increased blood flow to surface and increased fluid movement out the blood stream (oedema)
What affect does histamine have in mucosae?
Constriction of airways and contraction of smooth muscle in the intestine
What causes mast cell degranulation?
IgE antibodies is already bound to Fc-epsilon-R1
Circulating antigen binds IgE, causing receptor crosslinking and degranulation
How are IgE produced?
The CD4 T helper cells causes a class switch to IgE production
What is an allergen?
An antigen which causes an allergic type IgE-mediated response
What causes rashes and puffy skin seen in anaphylaxis?
Histamine causes vasodilation leading to red skin colour and oedema leading to raised appearance
What is skin rash called?
Urticaria
When can the localised skin reaction seen in allergy be useful?
In skin prick tests to see if allergens cause a wheal-and-flare reaction
What is hay fever called?
Allergic rhinitis
What causes Allergic Rhinitis?
Oedema in the epithelia lining the nose
Resulting in general irritation and mucus secretion
What causes asthma?
When the allergen reaches the bronchioles of the lungs, resulting in contraction of smooth muscles which reduces the diameter of the airways
Leads to increased mucus production and difficulty breathing in and out
What causes food allergies?
When an allergen is ingested, it acts on the mucosal mast cells in the intestinal tract, leading to vomiting and diarrhoea
If absorbed into blood stream, can cause rashes or itching
What occurs in anaphylaxis which can be fatal and affect organ function?
A rapid decrease in blood pressure as the blood vessels dilate (shock)
Why is adrenaline (epinephrine) given as an emergency treatment for anaphylaxis?
Adrenaline acts on alpha-adrenergic receptors to cause vasoconstriction and beta-adrenergic receptors for bronchodilation and redirects blood to organs to prevent shock
After adrenaline, what medication is given following an anaphylactic shock?
Anti-histamines and anti-inflammatory corticosteroids like hydrocortisone
If breathing problems persist after anaphylactic shock, what would be necessary?
Oxygen and bronchodilator given via inhaler (e.g. salbutamol)
Why do patients feel faint follow an anaphylactic shock?
Due to the dramatic loss of blood pressure (hypotension)
Why is blood pressure carefully measured after a shock?
Provides a reliable indication of recovery
What is biphasic anaphylaxis?
When the symptoms return within hours of the initial reaction
How long should patients with moderate respiratory/cardiovascular compromise should be observed before discharge?
8-10 hours
