How Your Body Fights Germs and Illnesses

Understanding Microorganisms and Disease

Viruses (e.g., flu, polio, common cold, AIDS, Ebola, chickenpox, measles, rubella, smallpox, mumps) are microscopic, measured in nanometers. Bacteria (e.g., tuberculosis, botulism, meningitis, tonsillitis, bronchitis, cystitis) are visible with an optical microscope, typically 1-5 micrometers. Fungi (e.g., athlete's foot, thrush, ringworm, candidiasis) are visible with an optical microscope, around 50 micrometers. Protozoa (e.g., malaria, dysentery) are also visible with an optical microscope, around 50 micrometers.

These microorganisms cause infectious diseases, which are illnesses that can spread to other people. Diseases not caused by pathogens are known as non-infectious diseases.

Vectors and Lifestyle Factors

• Vectors: Living organisms that transmit microorganisms.
• Lifestyle-Causing Disorders:
  • A diet high in sugar can lead to diabetes.
  • Insufficient vitamin C intake can cause scurvy.
  • Anemia, often due to inadequate iron intake, is not always lifestyle-related.
  • A healthy diet and avoiding smoking reduce cancer risk.

Some diseases are also inherited.

Protection Against Microorganisms

• First Line of Defense: Includes skin, blood clotting, mucous membranes, and hydrochloric acid to protect against pathogens.
• Second Line of Defense: White blood cells are a crucial part of our immune system.

Immunization can protect against diseases like measles and mumps. As new diseases emerge, new drugs are developed. Antibiotics are effective against bacteria but not viruses. New drugs require rigorous testing.

How Pathogens Cause Symptoms

Symptoms arise when pathogens damage cells or produce toxins. Pathogens possess antigens on their surface, which are recognized by white blood cells (WBCs).

Types of White Blood Cells

• Phagocytes: These cells engulf and destroy microbes and typically have a lobulated nucleus.
• Lymphocytes: These cells produce antibodies, which are proteins. They have a large nucleus and are highly specific. Memory lymphocytes are specialized to recognize a specific illness, and some antibodies can remain in the bloodstream after an infection, providing lasting immunity (memory antibodies).

Types of Immunity

• Active Immunity: The body actively produces its own antibodies.
  • Natural Active Immunity: Occurs when a pathogen invades the body.
  • Artificial Active Immunity: Achieved through vaccination with a weakened pathogen.
• Passive Immunity: The body receives pre-made antibodies.
  • Natural Passive Immunity: Transferred during pregnancy or breastfeeding.
  • Artificial Passive Immunity: Administered through injections.

Protoctists and Disease Transmission

Protoctists are single-celled organisms, some large enough to be seen without magnification. They can cause severe human illnesses. For example, the anopheles mosquito acts as a vector for Plasmodium, the parasite that causes malaria. Plasmodium multiplies within the mosquito's stomach before migrating to the salivary glands.

The Life Cycle of Plasmodium (Malaria)

1. An infected mosquito transmits Plasmodium parasites to a human.
2. Parasites rapidly multiply in the human liver and are then released into the bloodstream.
3. They invade red blood cells, feeding on hemoglobin and dividing. This causes red blood cells to burst, releasing more parasites into the blood, leading to symptoms like tiredness and fever.
4. An uninfected mosquito ingests the parasite when feeding on infected human blood.

Mosquito eggs are laid in water, hatching into larvae and then pupae, which stay near the surface to access oxygen.