Class 7 Biology: Allergies

Introduction

• Lecturer: दीपिका फ्रॉम लर्न हब
• Free learning platform: learn.com
• Discussion about the last chapter of Class 7 Biology – Allergies
• Focus: Understanding allergies in detail

What is an Allergy?

• Symptoms: Skin rashes, redness, heated feeling, continuous sneezing due to wind exposure
• Definition: Allergy is the concept introduced in 1906 by Viennese pediatrician Clemens von Pirquet.
  • Observed patients sensitive to otherwise harmless substances like dust, pollen, certain foods.
• Greek Meaning: 'Allos' meaning 'other' and 'ergon' meaning 'work' (
• Immune System's Role: Hypersensitivity response to certain substances (allergens)
  • In a group of 100 people, 10 may be hypersensitive, while 90 are not.

Common Allergens & Responses

• Examples of Allergens:
  • Dust, spores, pollen, insect stings, certain clothes, food (mushrooms, peanuts)
• Immune System Response: Produces immunoglobulins (Ig)
  • Specific proteins that protect the body from specific allergens.
  • Histamine: Inflammatory chemical triggered by allergens, producing allergy symptoms.
• Symptoms:
  • Inflammation, skin rashes, constriction of bronchi,
  • Running nose (allergic rhinitis), food allergies, allergic dermatitis, asthma predominantly in pollutant-heavy environments.

Entry Routes for Allergens

• Skin: Contact with latex, certain clothes, insect bites.
• Mouth: Foods (milk, soy, eggs, wheat, peanuts, fish, shellfish).
• Nose: Dust, pollen, chemicals, spores.

Signs and Symptoms of Allergies

• Airborne Allergens: Irritation of nose, continuous cough, sneezing, skin rashes, watery eyes.
• Food Allergens: Stomach pain, bloating, vomiting, skin itching/swelling.
• Insect Bites & Antibiotics: Severe allergic reactions (anaphylaxis), multiple organ involvement, redness, rashes, low blood pressure.
• Common Reactions:
  • Hay Fever: Sensitivity to pollen, affecting nasal passages and eyes.
  • Asthma: Constriction of bronchi, making air passage narrow, leading to difficulty in breathing.
  • Hives: Swollen patches or pale red bumps on skin, response to food/medicines.
  • Anaphylaxis: Sudden allergic reaction causing blood pressure drop, can be life-threatening.

Precautions and Diagnosis

• Precautions:
  • Awareness of allergens and use of medications.
  • Anti-allergy shots, doctor consultation.
• Diagnosis:
  • Skin Prick Test: Intradermal exposure to allergens, checking for reaction (redness, swelling) after 30 minutes.
  • Blood Test: Analysis of blood sample for antibodies (IgE specific to allergens).

Questions

1. Name the inflammatory chemical released by basophils causing skin reaction and bronchi constriction.
   • Answer: Histamine
2. Which test is most favored for testing allergy: Prick test or Blood test, and why?
   • Answer: Blood test is favored because it is safer and can be conducted on a wider range of individuals.

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• Conclusion: Completion of Class 7 ICSE Biology syllabus.
• Reminder: Review all the videos and ask questions on learn.com if doubts arise.