Tutorial 5 - Anaphylactic Reaction Flashcards
Describe features of anaphylaxis?
Acute Type 1 Hypersensitivity reaction
Can be systemic
Due to IgE-mediated response to antigen
Describe IgE
- IgE response important against parasitic infections
- Normal pathway to activate lymphocytes occurs when antigen binds to surface IgM on lymphocytes
- Typically antibody secreted as IgM, then switches to IgG as immune response progresses.
What happens in Type 1 Hypersensitivity?
- CD4+ (Th2) activation causes a switch to IgE production.
- IgE binds to IgE receptors on the surface of mast cells.
- Many IgE binds to surface IgE receptors on mast cells. This causes mast cells to degranulate when exposed to antigen.
Where are mast cells distributed?
What are they in association with?
Distributed throughout body in connective tissue.
Associated with epithelial mucosae.
What do mast cells contain?
They contain granules of inflammatory mediators - notably histamines and leukotrienes.
These inflammatory mediators are released when antigen binds to surface IgE
Describe the action of inflammatory mediators.
- Act principally on blood vessels and smooth muscle.
Effects:
- Vasodilation
- Oedema - increased fluid movement out of blood
- Bronchoconstriction - shortness of breath
- Loss of blood volume due to extravasation of fluid. Leads to hypotension.
- Heart rate increases slightly but force of contraction decreases. - Smooth muscle contraction in small intestine walls.
Describe skin allergies.
- Connective tissue mast cells stimulated. Causes vasodilation (gives red appearance) and oedema leading to raised appearance. (type of rash = urticaria)
- If allergen inhaled, main site of action is in mucosal mast cells of respiratory system.
- If in nasal passages, causes oedema in epithelial lining of nose. Causes general irritation and stimulates mucus secretion. (THIS IS ALLERGIC RHINITIS - hay fever)
- If allergen reaches lung bronchioles - contraction of smooth muscle. Decreases airway diameter, inflammation and increased mucus production. Results in ASTHMA.
What is urticaria used for?
Allergy testing. Pin prick followed by checking for wheal and flare reaction.
What happens if allergen is ingested?
Acts on mucosal mast cells in intestinal tract.
Leads to vomiting and diarrhoea.
May also cause skin symptoms if absorbed into bloodstream.
What is anaphylaxis?
Systemic response to allergen - causes immediate responses throughout body.
Can be fatal - must be treated as medical emergency
Dilation of peripheral blood vessels causes rashes and oedema.
What are the consequences of anaphylaxis?
- Dramatic drop in blood pressure. Can affect organ function. This is SHOCK.
- Bronchoconstriction causing breathing difficulty.
- Patient will have increased respiratory and heart rate.
(patients may also have nausea, abdominal cramps or diarrhoea)
Describe treatment of anaphylaxis.
- Emergency treatment initially aimed at hypotension. Inflammation afterwards.
- Patient laid down with feet raised- improves blood supply to head and trunk.
- Adrenaline given, IV drip to control blood pressure.
- Medications such as antihistamines and anti-inflammatory corticosteroids to control allergic response.
- Oxygen may be used and bronchodilators may be given.
What is the effect of adrenaline?
- Vessels - Vasoconstriction - reduces swelling and heat
- Lungs - bronchodilator - get rid of oedema
- Heart - increase heart rate and force of contraction. Must be careful not to give excess
What kind of substances can cause anaphylaxis?
Those that can travel freely around the body.
e.g. penicillin, drugs, venom, peanuts
What does adrenaline bind to?
B1 and b2 receptors.
B1 = heart
B2 = lung
