11.7-8

• Bacteria


  • Single-celled microorganisms
  • Pathogenic bacteria
  • Non-pathogenic bacteria
• There are approximately 10 times as many bacterial cells as human cells in the human body
• There is a large number of bacteria on skin and in the digestive tract
• The majority of these bacteria are rendered harmless by the immune system
• A few pathogenic bacteria cause infectious diseases
• Pathogenic bacteria


  Cause disease by dividing rapidly and producing toxins that harm the host’s body
• Bacterial cell structure


  • Glycocalyx
  • Flagella
  • Pili
• Glycocalyx


  A capsule common in pathogenic cells that protects against attack by white blood cells
• Flagella


  Enables motion
• Pili


  Hair-like extensions used to attach to other cells
• Binary Fission Reproduction


  1. Asexual reproduction

  2. Produces two identical daughter cells

  3. Every 20 minutes under ideal conditions

  4. Binary fission is the evolutionary precursor to mitosis
• To cause disease, pathogenic bacteria must gain access into the body
• Access routes for bacteria

  • Cuts
  • Contaminated food or water
  • Close contact with an infected person
  • Contact with the faeces of an infected person
  • Breathing in exhaled droplets
  • Touching contaminated surfaces
• How bacteria make us sick

  Multiply rapidly, crowd out host tissues<|>Killing cells and tissues outright<|>Producing toxins that can paralyse or destroy cells
• Helminths are eukaryotic, multicellular animals that usually have digestive, circulatory, nervous, excretory, and reproductive systems
• Helminths


  • Bilateral symmetry
  • Head and tail
  • Tissue differentiation (endoderm, mesoderm, ectoderm)
• Parasitic Helminths


  Spend most or all their lives in a host and usually lack a digestive system
• Specializations of Parasitic Helminths

  • Absorb nutrients from host
  • Reduced nervous system
  • Reduced or absent locomotion
  • Complex reproductive system
• Main groups of Helminths

  • Platyhelminths
  • Nematodes
• Platyhelminths (Flatworms)


  • Trematodes or Flukes
  • Cestodes or Tapeworms
• Trematodes or Flukes


  • Leaf shaped bodies
  • Ventral and oral suckers for attachment
  • Cause damage to blood vessels and organs
• Cestodes or Tapeworms


  • Intestinal parasites with long flat bodies
  • Lack a digestive system
  • Body made up of segments called proglottids
• Nematodes (Roundworms)


  Cylindrical body tapered at each end<|>Have a complete digestive system
• Nematodes


  • Body covered by tough cuticle
  • Most species are dioecious
  • Life cycle simpler than flatworms
• Infections caused by Nematodes

  • Infectious eggs
  • Infectious larvae
• Pinworm (Enterobius vermicularis)


  Spends entire life in human host<|>Causes itching
• Up to 90% of children are infected through contaminated clothes or bedding
• Adult Hookworm (Necator americanus)

  Live in small intestine of humans<|>Enter host by penetrating skin
• Hookworm eggs are excreted in feces
• Hookworm enters bloodstream, travels to lungs, swallowed in sputum
• Hookworm infection can be avoided by wearing shoes
• Portals of Entry


  • Respiratory System
  • Digestive System
  • Reproductive and Urinary Systems
  • Skin
• Types of Immunity


  • Non-specific
  • Specific
• Non-specific immunity


  Broadly effective, no prior exposure
• First Line of Defense

  External Barriers
• Second Line of Defense

  1. Phagocytic Cells

  2. Antimicrobial Proteins

  3. Inflammation

  4. Fever
• Specific immunity


  Results from prior exposure and results in protection against a specific pathogen
• Third Line of Defense

  Immune System
• Non-Specific Response


  • React in the same way to all infections
  • Have no memory
  • Level of response is the same for each infection of the same organism
• Specific Responses


  • React in a specific way
  • Have a memory
  • Much greater response on a second exposure to an infection
  • Can be acquired