7.1

• A pathogen is an agent that causes diseases. It enters the body and evades non-specific defences and patrolling phagocytes and granulocytes.
• Bacteria:

  • organism; lacks a nucleus
  • majority are non-pathogenic
  • RNA/DNA floats freely or as plasmids (loops)
  • 1-10 micrometres long
  • 0.5-2 micrometres in diameter
  • visible under a light microscope
• Virus:

  • infectious agent
  • all are pathogenic
  • RNA/DNA are inside a capsid
  • must infect an organism to reproduce
  • visible under electron microscopes
• Transmission of pathogens:

  • contagious - passed on by direct human contact
  • vector - agent capable of tranferring diseases to others
• Contact:

  Transmission Method: Direct/Indirect Physical Contact

  Examples: Skin infections, STIs
• Ingestion:

  Transmission Method: Ingestion of Food/Drink Contaminated with Pathogens

  Examples: Dysentery, Typhoid Fever, Salmonella
• Body Fluids:

  • Transmission Method: Body Fluids on an Infected Person Comes in Contact with Mucous Membranes or Bloodstream
  • Examples: Human Immunodeficiency Virus (HIV), Hepatitis B and C
• Droplets:

  • Transmission Method: Moisture Droplets Containing Pathogens Breathed in by Others
  • Examples: Ebola, COVID-19, Mumps, Colds, Influenza
• Airborne:

  • Transmission Method: Evaporation of Droplets Allows Pathogens to be Viable for a Greater Distance
  • Examples: Measles, Chickenpox
• Vectors:

  • Transmission Method: Transferred from Animals
  • Examples: Malaria and Dengue Fever from Mosquitos, Lyme Disease from Ticks
• External defences

  A) cerumen inhibits bacterial growth

  B) cleansed by tears and it inhibits bacterial growth

  C) hairs and mucus trap micro-organisms

  D) micro-organisms trapped and saliva cleanses mouth

  E) impervious barrier

  F) urine flow prevents bacterial growth

  G) mucus layer traps micro-organisms

  H) acidic juices kills many micro-organisms

  I) acidic secretions inhibit growth of pathogens

  J) mucous membrane traps micro-organisms

  
• non-specific defences - works against all pathogens

  specific defences - directed at a particular pathogen
• External defences:

  • skin
  • mucus
  • cilia
  • acids
• Skins:

  • not broken by cuts/abrasions → prevents entry of micro-organisms
  • special protection at openings of the skin (mouth, anus)
  • sebum - contains substances that kills some pathogenic bacteria
  • sweat - contains salts and fatty acids → prevents growth of many micro-organisms
• Mucus:

  • mucous membranes line body cavities opening to the exterior
  • mucus traps particles → inhibits entry of micro-organisms
• Hairs:

  • found in nasal cavity
  • hair and mucus traps up to 90% of particles in the nose
• Cilia:

  • contained in mucous membranes at the nasal cavity, the trachea and other air passages
  • beating action of cilia → moves mucus towards the throat → coughed up or swallowed
• Acids:

  • stomach juices are strongly acidic
  • kills many bacteria taken in with food
  • vagina juices has acid secretions → reduces micro-organism growth
  • urine and sweat are slightly acidic
• Lysozyme:

  • bacteria-killing enzyme
  • found in tears, saliva, sweat and secretions of the nose and tissue fluid
• Cerumen: (ear wax)

  • protects outer ear against infection
  • slightly acidic and ocntains lysozyme
• Movement of fluid:

  • flushing action of body fluids keeps certain areas pathogen-free
  • urine flowing through the urethra prevents bacterial growth
  • women have shorter urethras → more likely to suffer from bladder infections
  • tears, sweat and saliva involved in flushing and cleansing
• Protective reflexes:

  • sneezing
  • coughing
  • vomiting
  • diarrhoea
• Sneezing:

  (forceful expulsion of air from the lungs carrying mucus, foreign particles and irritating gases through the nose and mouth)

  • stimulus - irritations of the nasal cavity’s walls
  • may caused by noxious fumes or dust particles
• Coughing:

  (forceful expulsion of air from lungs to remove an irritant, driving mucus and foreign particles out the mouth and nose)

  • stimulus - irritation in the lower respiratory tract (bronchi and bronchioles)
• Vomiting:

  (contractions of the muscles of the abdomen and diaphragm which expels the stomach contents)

  • stimulus - psychological
  • induced by excessive stretching of the stomach and bacterial toxins
• Diarrhoea:

  (when materials do not stay in the large intestine long enough for water absorption, causing watery faeces)

  • caused by irriation of the intestines by bacteria, viruses or protozoans
  • causes increases contractions of the walls of the intestines
• Shapes of bacteria:

  • cocci - spherical; can be in clusters
  • bacilli - rod-like with flagella
  • spirilla - twisted cells
  • vibrio - curved; often shaped like a comma