section 1: disease & the immune system - topic 2: defence against pathogens Flashcards
what kind of defences do animals have against pathogens?
primary.
non-specific.
what are the animal defences?
the skin.
mucous membranes.
blood clotting.
inflammation.
wound repair.
expulsive reflexes.
how does the skin act as a defence?
it acts as a physical barrier - blocking pathogens from entering the body.
it also acts as a chemical barrier by producing chemicals that are antimicrobial (which destroy or slow the growth of microorganisms) and can lower pH, inhibiting the growth of pathogens.
how do mucous membranes act as defences?
they protect body openings that are exposed to the environment (i.e. mouth, nostrils, ears, genitals, anus).
some membranes secrete mucus - a sticky substance that traps pathogens and contains antimicrobial enzymes.
what is an example of mucous membranes acting as defences?
the gas-exchange system:
- if you breathe in air that contains pathogens, most of them will be trapped in mucus lining the lung epithelium (the outer layer of cells in the passages to the lungs).
- these cells also have cilia that beat and move the mucus up the trachea to the throat and mouth, where it’s removed.
how does blood clotting act as a defence?
a blood clot is a mesh of protein (fibrin) fibres.
blood clots plug wounds to prevent pathogen entry and blood loss.
- they’re formed by a series of chemical reactions that take place when platelets (fragments of cells in the blood) are exposed to damaged blood vessels.
how does inflammation work as a defence?
the signs of inflammation include swelling, pain, heat, redness.
- it can be triggered by tissue damage, as the damaged tissue releases molecules which increase the permeability of the blood vessels, so they start to leak fluid into the surrounding area.
- this causes swelling and helps to isolate any pathogens that may have entered the damaged tissue.
- the molecules also cause vasodilation, which increases blood flow to the affected area.
- this makes the area hot and brings white blood cells to the area to fight off any pathogens that may be present.
how does wound repair act as a defence?
- the skin is able to repair itself in the event of injury and re-form a barrier against pathogen entry.
- the surface is repaired by the outer layer of skin cells dividing and migrating to the edges of the wound.
- the tissue below the wound then contracts to bring the edges of the wound closer together.
- it is repaired using collagen fibres.
^ too many collagen fibres = scar.
how do expulsive reflexes act as defences?
include coughing and sneezing.
- a sneeze happens when the mucous membranes in the nostrils are irritated by things such as dust or dirt.
- a cough stems from irritation in the respiratory tract.
- both coughing and sneezing are an attempt to expel foreign objects, including pathogens, from the body.
^ they happen automatically.
what are the 2 types of plant defences?
physical.
chemical.
what are the plant physical defences?
a waxy cuticle.
cell walls.
the production of callose.
how does a waxy cuticle act as a defence?
it provides a physical barrier against pathogen entry.
it may also stop water collecting on the leaf, which could reduce the risk of infection by pathogens that are transferred between plants in water.
how do cell walls act as a defence?
they form a physical barrier against pathogens that make it past the waxy cuticle.
how does the production of callose act as a defence?
(it’s a polysaccharide)
it gets deposited between plant cell walls and plasma membranes during times of stress i.e. pathogen invasion.
- callose depositino may make it harder for pathogens to enter cells.
- callose deposition at the plasmodesmata (small channels in the cell walls) may limit the spread of viruses between cells.
what are the plant chemical defences?
the production of antimicrobial chemicals.
the secretion of chemicals that are toxic to animals.
