L7. Body defences

Question 1

Immunity

Answer 1

The state of being resistant to injury (by poisons, foreign proteins and invading pathogens) Also called resistance

Question 2

First Line Defences

Answer 2

• Prevent pathogens from entering body
• Non-specific
  > Skin
  > Mucous membranes
  > Hair and cilia
  > Gastric juices
  > Vaginal secretions
  > Urine flow
  > Tears, sweat, saliva
  > Cerumen (earwax)

Question 3

Physical and chemical properties of skin and mucous membranes
(1st line defence)

Answer 3

Skin- epidermis provides a formidable physical barrier
- Periodic shedding helps remove microbes at skin’s surface
Mucous membranes- lines body cavities and secretes fluid
- mucous traps many microbes and foreign substances

Question 4

Protects portals of entry to the body

1st line defence

Answer 4

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Question 5

Second-line defences

Answer 5

• Kill/ destroy pathogen if it breaches first line defence before any harm is done
• Non-specific
• Involves leukocytes
  > Phagocytosis
  > Fever
  > Inflammation
  > Antimicrobial compounds

Question 6

Antimicrobial substances 
(2nd line defences)

Answer 6

Discourages microbial growth of a pathogen
> Interferons (IFNs)
> Compliment system

Question 7

Phagocytes

2nd line defences

Answer 7

Body cells that engulf large solid particles

Question 8

Natural killer cells

2nd line defences

Answer 8

Attack any body cells that display abnormal or unusual plasma membrane proteins

Question 9

Inflammation

Answer 9

• Destroys and removes antigens: immune response
• Limits effects of injurious agent by slowing growth and replication of pathogen
• Cleans-up dead tissue and debris
• Promotes healing
  Signs of inflammation
  > Swelling
  > Redness
  > Heat
  > Pain
  > Loss of function

Question 10

Fever

Answer 10

• Intensifies effects of interferons
• Inhibits growth of some microbes
• Speeds up body reactions that aid repair

Question 11

Third line defences

Answer 11

• Specific immune response
• Host is exposed to pathogen
• Pathogens have surface antigens
• B and T lymphocytes are capable of recognising these antigens as ‘foreign’ and mount an attack
  > T-lymphocyte- cell mediated response
  > B-lymphocyte- humeral (anti-body) response

Question 12

Non-specific defences

Answer 12

• Innate
• General defence/ attack on all antigens
• Inborn
• First and second line defences

Question 13

Specific defences

Answer 13

• Acquired or adaptive
• Specialist/ target defence against one type of antigen
• Acquired during life
• Third line defences

Question 14

Describe the four general properties of specific defences

Answer 14

• Specific- activates a specific immune response (targeted to a specific pathogen)
• Versatile
• Memory- Memory T and B cells form so that the pathogen can be recognised immediately next time
• Tolerance

Question 15

How does the specific immune system retain an ‘immunological memory’ to protect against future infections?

Answer 15

• it takes part of the antigen and presents it on the surface, show it to a cytotoxic T cell
• Cytotoxic T cell will then recognise any cells that has this on its surface

Question 16

Cell-mediated immunity

Answer 16

• Macrophages engulf pathogens and present the antigen to the Cytotoxic T-cell
• The Cytotoxic T-cell will recognise any cell with this antigen and kill it directly by releasing chemicals eg. perforin
• Will also recognise infected cells and kill them via apoptosis
• Helper T-cells activate B cells to make antibodies
• Memory T-cells form so that the pathogen can be recognised immediately next time

Question 17

Antibody-mediated immunity (humoral immunity)

Answer 17

• B-lymphocytes encounter and recognise foreign antigen
• B-lymphocytes differentiate into plasma cells and make antibodies to that specific antigen
• Memory B-cells also form so that the pathogen can be recognised immediately next time

Question 18

Antigens as “triggers” for B and T cell activation

Answer 18

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