12.5 : Non - Specific Animal Defences Flashcards
List the barriers animals have against infection
Skin Mucous membranes Blood clotting Inflammation Wound repair Expulsive reflexes
How is skin a barrier?
Physical barrier - blocks pathogens from entering the body
Chemical barrier - produces chemicals that are antimicrobial and can lower pH, inhibiting growth of pathogens
Has skin flora of healthy micro organisms that outcompete pathogens for space.
Sebum inhibits growth of pathogens.
How are mucous membranes a barrier?
They protect body openings that are exposed to the environment.
The mucus is a sticky substance that traps pathogens and contain lysozymes which destroy bacterial and fungal cell walls.
It also contains phagocytes which remove remaining pathogens.
How is blood clotting a barrier?
Blood clot = mesh of protein ( fibrin ) fibres.
They plug wounds to prevent pathogen entry and blood loss.
They’re formed by a series of chemical reactions that take place when platelets are exposed to damaged blood vessels.
Thromboplastin is an enzyme that triggers a cascade of reactions resulting in the formation of a blood clot.
Serotonin makes the smooth muscle in the walls of the blood vessels contract so they narrow abs reduce the supply of blood to the area.
How does wound repair act as a barrier?
The skin can repair itself and re-form a barrier against pathogen entry.
Epidermal cells below the scab start to grow and damaged blood vessels regrow.
Surface is repaired by outer layer of skin cells dividing and migrating to edges of the wound.
Tissue below wound then contracts to bring the edges of the wound closer together. It is repaired using collagen fibres.
How does inflammation act as a barrier?
Signs of inflammation : swelling, pain, heat and redness.
Mast cells are activated in damaged tissue and release chemicals called histamines and cytokines.
Histamines make blood vessels dilate ( causes localised pain and redness ). Raised temperature helps prevent pathogens reproducing.
Histamines make blood vessel walls more leaky so blood plasma is forced out and forms tissue fluid which causes oedema and pain.
Cytokines attract phagocytes to the site and they dispose of pathogens by phagocytosis.
How do expulsive reflexes act as a barrier?
Coughs and sneezes eject pathogen - laden mucus from the gas exchange system.
Vomiting and diarrhoea expel the contents of the gut along with any infective pathogens.
How do fevers act as a barrier?
Cytokines stimulate your hypothalamus to reset the thermostat and your temperature goes up.
This high temperature inhibits pathogen reproduction.
Also, the specific immune system works faster at higher temperatures.
What are phagocytes? What are the two types?
Specialised white cells that engulf and destroy pathogens. Involved in the non-specific immune response.
Two types : neutrophils and macrophages
Describe the stages of phagocytosis
- Pathogen produces chemicals that attract phagocytes.
- Phagocytes recognise antigen ( non-human protein) on pathogen.
- Phagocyte engulfs the pathogen and encloses it in a vacuole called a phagosome.
- Phagosome combines with a lysosome to form a phagolysosome.
- Enzymes from lysosome digest and destroy the pathogen.
What happens when a macrophage has digested a pathogen?
It combines antigens from the pathogen surface membrane with special glycoproteins in the cytoplasm called the major histocompatibility complex.
The MHC complex moves these pathogen antigens to the macrophages own surface membrane, becoming an antigen - presenting cell.
These antigens now stimulate other cells involved in the immune system response.
Why are cytokines and opsonins useful in phagocytosis?
Cytokines act as cell - signalling molecules, informing other phagocytes that the body is under attack and stimulating them to move to the site of infection / inflammation.
Opsonins bind to pathogens and ‘tag’ them so they can be more easily recognised by phagocytes. Phagocytes have receptors on their cell membranes that bind to opsonins, and the phagocyte then engulfs the pathogen.
