module 4 - 12.5 non-specific animal defences against pathogens

Question 1

when are the primary non-specific defences against pathogens present?

Answer 1

always, or are activated very rapidly

Question 2

how is the skin a barrier to keep pathogens out?

Answer 2

• cover body and prevents entry of pathogens
• too thick for pathogens to get through
• has lots of healthy organisms that outcompete pathogens for space on body surface

Question 3

how is the body tracts/airways lines with mucous membranes, a non-specific defence?

Answer 3

• secrete sticky mucus
• traps microorganisms and contains lysozymes which destroy bacterial and fungal cell walls
• also contains phagocytes, prevents pathogens entering the body

Question 4

how do expulsive reflexes help get rid of pathogens?

Answer 4

• coughs and sneezes eject pathogen-laden mucus from gas exchange system
• vomiting and diarrhoea expel contents of gut along with pathogens

Question 5

when we cut our skin, pathogens can enter through the wound, how do we stop this?

Answer 5

• blood clots rapidly to seal wound
• when platelets come into contact with collagen in skin or wall of damaged blood vessel, they adhere & begin secreting substances

Question 6

what substances do the platelets secrete?

Answer 6

• thromboplastin - enzyme triggers formation of a blood clot
• serotonin - makes smooth muscle in walls of blood vessel contract, reduce blood supply to area

Question 7

what is the first stage of wound repair?

Answer 7

clot dries out and forms tough, hard scab on surface, stops pathogens entering

Question 8

what starts to grow beneath the scab and why?

Answer 8

• epidermal cells
• seals wound permanently while damaged blood vessels grow
• collagen fibres deposited to give new tissue strength

Question 9

what is the inflammatory response?

Answer 9

localised response to pathogens resulting in inflammation at the site of a wound

Question 10

mast cells are activated in damaged tissue and release chemicals called histamines and cytokines, what are histamines and cytokines?

Answer 10

histamines - make blood vessels dilate, cause heat and redness, raised temp helps stop pathogens from reproducing
histamines - make blood vessels more leaky so blood plasma is forces out, then its tissue fluid which causes swelling
- cytokines - attract white blood cells to the site, dispose of pathogens by phagocytosis

Question 11

what happens if the pathogens get into the body?

Answer 11

the next lines of defence are adaptations to prevent them growing, or to destroy them

Question 12

how are fevers a defence against pathogens?

Answer 12

• most pathogens reproduce best at or below 37C, higher temperatures inhibit pathogen reproduction
• specific immune system works faster at higher temperatures

Question 13

what are phagocytes?

Answer 13

specialised white blood cells that engulf and destroy pathogens
- 2 types: neutrophils and macrophages

Question 14

what do phagocytes do?

Answer 14

build up at the site of infection and attack pathogens

Question 15

what are the stages of phagocytosis?

Answer 15

1. pathogens produce chemicals that attract phagocytes
2. phagocytes recognise non-human proteins on the pathogen (response to non-specific pathogen)
3. phagocyte engulfs the pathogen and encloses it in vacuole called phagosome
4. enzymes from lysosome digest and destroy the pathogen

Question 16

what happens when a macrophage has digested a pathogen?

Answer 16

it combines antigens from the pathogen surface membrane with glycogproteins in cytoplasm called MAJOR HISTOCOMPATIBILITY COMPLEX

Question 17

what does the major histocompatability complex do?

Answer 17

move the pathogen antigens onto the macrophages own surface membrane - becomes an ANTIGEN-PRESENTING CELL

Question 18

what do antigen preventing cells do?

Answer 18

stimulate other cells involved in the specific immune response

Question 19

what are the helpful chemicals within the non-specific animal defences against pathogens?

Answer 19

cytokines and opsonins

Question 20

how are cytokines helpful chemicals?

Answer 20

• act as cell-signalling molecules
• inform other phogocytes that the body is under attack - stimulates phagocytes to move to site of infection
• can also raise body temp & stimulate specific immune system

Question 21

how are opsonins helpful chemicals?

Answer 21

• bind to pathogens and ‘tag’ them - can be more easily regocnised by phagocytes
• phagocytes have receptors on cell membranes that bind to common opsonins