Organisation and Maintenance of Organisms - Diseases and Immunity

Diseases and Immunity

Understanding Disease

  • Definition of Disease: A state where the body cannot maintain optimal conditions due to a failure in homeostasis.
  • Homeostasis maintains optimal conditions for body function.
  • When homeostasis fails, the body shows signs (e.g., raised temperature) and symptoms (e.g., fatigue).

Types of Diseases

  • Infectious Diseases:
    • Caused by pathogens (living organisms, usually microorganisms).
    • Transmissible from one individual to another.
    • Examples:
      • Cholera (bacteria in infected water)
      • Influenza (virus in air droplets)
      • Athlete's foot (fungus via direct contact)
      • Malaria (Plasmodium protoctist via Anopheles mosquito)
      • AIDS (HIV virus via body fluids)
  • Non-Infectious Diseases:
    • Not transmissible; caused by various factors.
    • Examples:
      • Degenerative diseases (e.g., heart attacks, cataracts) due to aging and free radicals.
      • Deficiency diseases (e.g., scurvy from vitamin C deficiency).
      • Allergies (e.g., hay fever from pollen).
      • Environmental diseases (e.g., skin cancer from UV radiation).
      • Inherited/metabolic diseases (e.g., sickle cell anemia, cystic fibrosis, diabetes) due to gene alterations.
      • Psychological/mental disorders (e.g., schizophrenia, depression) due to brain changes.
      • Self-induced diseases (e.g., lung cancer from smoking, cirrhosis from alcohol).

Symptoms of Disease

  • Sweating/fever: Due to resetting of the body's thermostat.
  • Vomiting/diarrhea: Due to the body's attempt to clear irritants.
  • Pain: Due to the release of toxins by pathogens.

Disease Patterns

  • Infectious diseases were major killers in the past (e.g., bacterial infections in the 18th century).
  • Antibiotics, immunization, and hygiene have reduced infectious disease deaths.
  • Smallpox has been eliminated through vaccination.
  • 'Diseases of affluence' (e.g., heart disease, cancer) are now major killers in the Western world.
  • Linked to lifestyle factors like smoking, diet, and exercise.
  • Vector-borne diseases (e.g., malaria) are confined to regions where the vectors live.

Spread of Infectious Diseases

  • Factors influencing the spread:
    • Air travel: Diseases spread rapidly across countries (e.g., COVID-19).
    • Global warming: Expansion of insect vector ranges.
    • Communal eating: Easier transmission of food poisoning organisms.

Pathogens and Parasitism

  • Pathogen Definition: An organism that causes disease by affecting the body.
  • Parasites: Pathogens are parasites that live on a host and cause harm.
  • Mechanisms of harm:
    • Secreting toxins (e.g., Clostridium botulinum producing nerve poison, Salmonella releasing gut-irritating toxin).
    • Rapid multiplication causing direct damage (e.g., malaria) or resource depletion (e.g., polio).
    • Immune response causing swelling, soreness, and fever.

Types of Pathogens

  • Viruses:
    • Size: ~1 nm.
    • Examples: Influenza, AIDS.
    • Cannot reproduce outside host cells; obligate parasites.
    • Require electron microscopes for study.
  • Bacteria (Prokaryotes):
    • Size: ~1 μm.
    • Examples: Cholera, food poisoning, TB.
    • TB deaths are high due to:
      • Poor disease control.
      • Antibiotic resistance.
      • HIV co-infection.
      • Increase in susceptible young adults.
    • Bacterial diseases can be treated with antibiotics.
  • Protoctists:
    • Size: Up to 1 mm.
    • Examples: Dysentery, malaria.
  • Fungi:
    • Size: May be extensive.
    • Examples: Athlete's foot, ringworm.
  • 'Worms':
    • Size: Up to several meters.
    • Examples: Tapeworm, Toxocara.

Controlling Disease Spread

  • Hygienic food preparation
  • Good personal hygiene
  • Proper waste disposal
  • Effective sewage treatment

Preventing Disease: Safe Food

  • Protecting food from microorganisms:
    • Prevent spoilage by decomposers.
    • Prevent disease by pathogens.

Food Poisoning

  • Caused by contaminated food with harmful microbes.
  • Symptoms result from:
    • Microorganisms feeding on host tissues.
    • Toxins released by microorganisms in food or inside the host.
  • Bacteria causing food poisoning:
    • Clostridium botulinum (deadly nerve toxin).
    • Listeria monocytogenes (in soft cheeses).
    • Salmonella group.
  • Thorough cooking kills bacteria, but contamination can occur afterward.

Principles of Good Food Hygiene

  • Avoid contamination by washing hands, utensils, and surfaces.
  • Prevent bacterial multiplication.
  • Destroy remaining bacteria by cooking thoroughly.
  • High-risk foods:
    • Undercooked meats and poultry.
    • Cooked rice.
    • Shellfish.
    • Dishes made with raw eggs.
  • Symptoms develop 8-36 hours after eating, leading to dehydration.

Fighting Disease Together

  • Three levels of responsibility:
    • Personal.
    • Community.
    • Worldwide.
Personal Responsibility
  • Good hygiene.
  • Balanced diet.
  • Regular exercise.
  • No smoking.
  • Controlled alcohol intake.
Community Responsibility
  • Safe drinking water and sewage treatment.
  • Refuse removal.
  • Medical care.
  • Health and hygiene standards monitoring.
Refuse Disposal
  • Landfill:
    • Advantages:
      • Land reclamation.
      • Economical use of space.
      • Away from residential areas.
    • Disadvantages:
      • Attracts pests.
      • Ecological damage.
    • Refuse buried under soil for decomposition; generates biogas.
    • Biodegradable vs. non-biodegradable materials.
  • Incineration:
    • Advantages:
      • Small land use.
      • No pest attraction.
      • Heat generation.
    • Disadvantages:
      • Toxic fumes.
      • Expensive to build.
      • Groundwater pollution.
      • Fuel consumption.
Worldwide Responsibility
  • World Health Organization (WHO): Aims to improve global health.
  • Successes:
    • Reduced infant mortality.
    • Smallpox elimination.
    • Malaria reduction.
    • Improved safe water provision.

Combating Infection: Blood and Defense

  • Disease caused by pathogen invasion leading to infection.
Skin Defense
  • Epidermis: Waxy, impermeable to water and pathogens.
  • Natural gaps protected by secretions:
    • Mouth protected by stomach acid.
    • Eyes protected by lysozyme in tears.
    • Ears protected by bactericidal wax.
  • Respiratory pathways protected by cilia and mucus.
Blood and Clotting
  • Blood clotting seals wounds and prevents pathogen entry.
  • Clotting depends on platelets and blood proteins.
  • Inherited defects (e.g., hemophilia) cause severe bleeding.
  • Histamine release causes inflammation and dilutes toxins.
White Blood Cells
  • Remove or destroy invading organisms.
  • Recognize foreign particles (antigens) without attacking body's own cells.
  • Antigens present on pathogen surfaces.
Phagocytosis

  • Phagocytes engulf and destroy pathogens with digestive enzymes.

  • Process:

    • Phagocyte recognizes and flows round pathogen, enclosing it in a sac.
    • Digestive enzymes are poured into the sac.
    • The pathogen is destroyed.
    • The phagocyte may absorb the digested products.
    • Pus contains dead phagocytes.

  • Phagocytes patrol exposed surfaces like lungs.

  • Free radicals (e.g., tobacco smoke) can lead to emphysema.

  • First aid addresses blood loss by applying pressure and avoiding unnecessary movement.

Pathogen Evasion
  • Hiding inside host cells (e.g., Plasmodium in liver cells).
  • Staying in phagocyte-free areas (e.g., inside the gut).

Antibodies and Immunity

  • Antibody Definition: A protein produced by the body in response to an antigen.
  • Lymphocytes (white blood cells) produce antibodies.
  • Each antigen stimulates production of a specific antibody.
  • Humans can make ~1,000,000 different antibodies.
Lymphocyte Action
  • Lymphocytes learn to make specific antibodies.
  • Body recovers as organisms are destroyed.
  • Symptoms (e.g., high temperature) occur during antibody production.
Immunity
  • Memory cells: Lymphocytes retained for future attacks.
  • Long-lasting protection against the same antigen.
Types of Immunity
  • Natural Active:
    • Individual makes own antibodies after infection.
    • Long-term immunity.
    • Example: Immunity to cold strains.
  • Artificial Active:
    • Vaccination stimulates antibody production.
    • Long-term immunity.
    • Example: Rubella vaccination.
  • Natural Passive:
    • Mother's antibodies cross placenta or in breast milk.
    • Short-term immunity.
    • Example: Newborn immunity to gut infections.
  • Artificial Passive:
    • Injection of ready-made antibodies.
    • Short-term immunity.
    • Example: Anti-tetanus injection.
Vaccination
  • Vaccines provoke the immune system to make antibodies.
  • Reduce disease spread by protecting individuals.
Problems with the Immune Response
  • Autoimmune Diseases:
    • Body produces antibodies against its own cells.
    • Example: Type I diabetes (destroys insulin-producing cells).
  • Transplant Rejection:
    • Recipient's lymphocytes recognize donor organ antigens as foreign.
    • Addressed by:
      • Immunosuppressant drugs.
      • Tissue matching.
Monoclonal Antibodies
  • Produced by hybridomas (lymphocytes + tumor cells).
  • Hybridomas produce large quantities of one desirable antibody.
  • Used in medicine, industry, and research.