anaphylaxis Flashcards
What type of cell causes the symptoms in type one hypersensitivity?
What is the signalling molecule involved?
Mast cell
Histamine
Mast cells contain prominent granules which contain mediators of inflammation, notably histamine and leukotrienes.
What tissues is the effect of histamine on?
How does it differ between blood vessels and epithelial?
The inflammatory mediators released by mast cells act principally on blood vessels and smooth muscle.
In connective tissue histamine causes dilatation of vessels with increased blood flow to the surface and increased movement of fluid out of the blood stream (oedema).
Around mucosae the opposite effect occurs, causing constriction of airways and contraction of the smooth muscle in the walls of the intestines.
What immunoglobulin class is likely to be involved?
Immunoglobulin E
Histamine and leukotrienes are secreted following antigen binding to the cell surface IgE.
IgE becomes bound to specific binding sites (IgE-receptors) found on the surface of mast cells, and it is the subsequent stimulation of these cells by exposure to the antigen that causes allergic or anaphylactic responses
what is the normal pathway of lymphocyte activation and how is type one hypersensitivity different ?
where antigen binds to the surface IgM on lymphocytes to stimulate proliferation and secretion of antibody.
Usually the antibody initially secreted is IgM, and this switches to IgG as the immune response progresses.
In type I hypersensitivity, activation of CD4+ T helper cells (TH2) causes a switch to IgE production
What causes the rashes and puffy skin?
If the patient has a skin allergy, stimulation of connective tissue mast cells causes vasodilatation leading to the red colour of the skin rash, and increased fluid out of bloodstream leading to oedema hence its raised appearance.
This type of rash is often called urticaria
how is a skin prick test carried out ?
hat allergens cause skin reaction?
The localised skin reaction is used in allergy testing, where small amounts of possible allergens are injected by pin-prick to see if they cause this kind of localised wheal-and-flare reaction.
Substances known to be capable of causing skin allergies include animal hair, proteins in natural latex, certain chemicals, substances in insect and plant stings.
How does Hay fever (allergic Rhinitis) come about?
If the allergen is inhaled, the principal site of action will be mucosal mast cells of the respiratory system.
If this is principally in the nasal passages, the effect will be oedema in the epithelia lining the nose and a consequent general irritation including stimulation of mucus secretion.
How does Asthma come about?
What allergens cause hayfever and asthma?
If the allergen reaches the bronchioles of the lungs then there will be contraction of smooth muscle reducing the diameter of the airways
also inflammation and increased mucus production, so there is difficulty breathing in and (especially) breathing out
Substances known to be capable of causing hay fever and asthma include pollens, faeces of dust mites, and proteins from animal hairs.
Why should adrenaline have been given?
blood vessel dilation results in a dramatic drop in blood pressure which can affect organ function: this is known as shock.
An injection of adrenaline will act to constrict peripheral blood vessels and redirect blood to the organs.
The patient is lain down with feet raised in order to improve blood supply to the head and trunk.
Why did the patient feel faint?
Due to the dramatic drop in blood pressure (hypotension).
Syncope (fainting) is a temporary loss of consciousness usually related to insufficient blood flow to the brain.
patients are initially laid down with their legs raised to counteract this.
Why was blood pressure monitored in hospital?
What is it called when occasionally, the symptoms return (usually within hours of the initial reaction)?
how long should patients be observed for if they have moderate respiratory or cardiovascular compromise?
Monitoring of blood pressure provides a reliable indication of recovery.
This is known as biphasic anaphylaxis.
8-10 hours before discharge.
