Minor Ailments - Allergy & hay fever Flashcards
What is allergy?
- Immune system reacting to a normally harmless substance
- Allergen – a substance that triggers allergy
- Some people are more prone to allergy than others= have genetic disposition
- Risk factors:
Heredity, gender, race, & age - Environmental factors
- Early exposure might be protective
- Environmental pollution, allergen levels & dietary changes
- Allergic disorders – asthma, eczema, hay fever= ATOPIC TRAID @ hugher risk i.e if s/o has asthma which is triggered by allergens they have a higher risk of ecezema & hayfever
Mechanism
- First-time exposure = mild reaction
- Repeated exposure = more serious reaction ; of primed mast cells
- A person is sensitized = limited exposure to a very small amount of allergen can trigger a severe reaction ; of primed mast cells
- Timeframe - seconds or minutes after exposure to the allergen, but some can be prolonged (ingestion). Rare after 24 hours.
- IgE mediated reactions = Type I (immediate) hypersensitivity
Atopy= atopic triad: - Genetic predisposition to make IgE antibodies in response to allergen exposure
- Allergic rhinitis, allergic asthma, atopic dermatitis are the most common manifestation of atopy
What sites can be affected
Allergic reactions
- Affects allergy prone individuals
1. Allergen such as pollen enters body
(skin, inhalation, ingestion, injection)
2. Activates B cells (plasma cells) to produce Immunoglobulin ( spedific to the allergen) E (IgE) Antibodies to the allergen - Released into blood stream
- Bind mast cells (abundant in the mucosa of the respiratory,
gastrointestinal tracts and in the skin) which then become primed
3. Future exposure to the allergen - Primed mast cells degranulation
- Histamine release into local tissue
- If they meet the allergen again it will release those cytokines into the blood stream
4. Allergy symptoms
Actions of Histamine on H1 Receptors
- Causes allergic reactions
- Local hormone (autocoid) auto = produced by the cell
autocoid = local reaction - Blood vessels – dilatation + capillary permeability increased (oedema) = Causes blood vessels to dilate & makes them become leaky leading to oedema and skin itch and anaphylactic shock
- Smooth muscle – contraction in lungs = broncho constriction = can’t breathe
- Skin – itch = senosry nerve endings
- Anaphylactic shock
- circulatory collapse &
bronchoconstriction – largely
mediated by histamine
Allergens – Type 1 hypersensitivity causes
- Proteins (e.g., foreign serum, vaccines)
- Plant pollens (e.g., rye grass, ragweed, timothy grass, birch trees)
- Drugs (e.g., penicillin, sulfonamide(old school antiobiotic caused people skin to drop off) - drugs, local anaesthetics, salicylate-drugs= i.e aspirin )
- Foods (e.g., nuts, seafood, eggs, peas, beans, milk)
- Insect products (e.g., bee venom, wasp venom, ant venom, dust mites, cockroach calyx, animal hair, animal dander)
- Mold spores
Actions of Histamine on the skin - Triple response of Lewis
Firm scratch of skin
1- red line (15s)= Capillary dilation
2- flare around line (45s) =Arteriolar dilation
3- Wheal (3 mins)=Exudation of fluid
- Caused by histamine
Symptoms of allergy
- Sneezing
- Wheezing
- Sinus pain
- Runny nose (rhinorrhoea)
- Cough
- Vomiting & diarrhoea
- Urticaria (hives)
Prevention
- Best way = to avoid (even for milder cases):
to narrow down what the allergen is good history taking is needed & read labels - Serious allergic reactions:
Medical ID tag – Wear a tag/bracelet
carry emergency medicines (e.g., im adrenaline autoinjector pens= reverse effects of histamine release) - Histamine constrict bronchioles adrenaline will relax them
- histamine dilates blood vessels adrenaline constricts them
Allergic Rhinitis
- Inflammation of the inside of the nose resulting in sneezing attacks & nasal discharge or blockage
- 1 in 5 people in the uk are affected
- ## can have a profound impact on quality of life, work and education
allergic rhinitis, Long-term problems due to
inflammation
Continous inflammation can cause:
* Nasal polyps (benign sacs of fluid in the nasal passages and sinuses)
* Sinusitis – infection – caused by swelling and inflammation preventing mucus drainage from the sinuses
* Middle ear infection
Symptoms of allergic rhinitis
w/ frequent bouts of sneezing =
- nasal congestion
- red, ithcy swollen eyes
can persist for weeks affecting:
- concentration
- sleep
- atendace @ work or school
what are the 3 types of allergic rhinitis
1. Seasonal (hay fever)
* usually outdoor allergens, pollen, moulds
(Tree pollen: February to April
Grass pollen: May to August
Fungal spores: Sept to October)
* Symptoms > 1hr a day (usually less than 4 weeks)
2. Perennial
* indoor allergens e.g., house dust mites, moulds,
animal (pets) dander (skin flakes)
* Symptoms year-round constant – perennial (> 4
weeks)
3. Occupational
* allergens at work e.g., dust from wood, flour, latex
* s/t in the work in environment that causing s/o to have a reaction
Antihistamines
- H1 receptor antagonists (antihistamines)
- Reversible binding to the H1 receptor
- More effective at preventing than reversing symptoms
- Block triple response of Lewis
- Partially prevent hypotensive effect
- No effect on gastric secretions (H2 receptors antagonists needed for that)
- Competes w/ the histamine in the system for the receptor
- Bocks what histamine does
- No effect on gastric effects
Management- Non-Pharmacological
- Allergen avoidance= best
- hay fever:
- Monitor pollen counts
- Keep windows closed/stay indoors
- Wrap-around sunglasses= stops pollen getting in eyes
- Vaseline around nose to stop it form getting into nasal passages
- Persistent allergic rhinitis:
- Exclude pets from certain living areas
- Acaricidal sprays & bedroom cleaning regimens
- Minimising carpets & soft furnishings, allergen-impermeable fabric bedding
- Self-care treatments such as saline nasal washes may (limited evidence)
Antihistamines
