Non-specific animal defences

what are primary defences?

the initial barriers that prevent pathogens entering the body

what happens if pathogens get past the primary defences?

they enter the body and further secondary defences will attempt to destroy the pathogen

what are the primary defences?

• the skin

• tears from eye

• mucous membranes

• stomach

• expulsive reflexes

• blood clotting

how does the skin work as a primary defence?

• physical barrier - blocks pathogens from entering the body

• chemical barrier - produces antimicrobial chemicals that destroy or slow the growth of microorganisms; lower pH inhibiting growth of pathogens

how does the eye work as a primary defence?

• tears contain antibodies and the enzyme lysozyme

how does the mucous membrane work as a primary defence?

• protect body openings that are exposed to the environment (e.g. mouth, nostrils etc.)

• secrete mucus that both traps pathogens and secretes antimicrobial chemicals

• e.g. the gas exchange system: pathogens trapped in mucus lining in the lung epithelium produced by the goblet cells. the ciliated epithelial cells in the lining have cilia that beat the mucus up throat and towards mouth where it leaves

how does the stomach have primary defences?

• if pathogens make it to stomach they would be killed by stomach acid (strong hydrochloric acid)

how do expulsive reflexes work as a primary defence?

• include coughing and sneezing

• a sneeze happens when the mucus membranes in the nostrils are irritated by things like dust

• a cough stems from irritation in the respiratory tract

• expulsive reflexes happen automatically

• This expelled air contains secretions from the respiratory tract along with the foreign particles that have entered

how does blood clotting act as a primary defence?

1. cut

2. platelets release substances, via a cascade of events, result in the formation of fibrin

3. fibrin forms a network, trapping platelets and forming a clot

what are platelets and what do they do?

• irregularly shaped colourless bodies that are present in the blood

• their sticky surfaces lets them, along with other substances, form clots to stop bleeding

what does blood clotting do and is it always good?

coagulation needs to occur at sites of injury

• prevents entry of pathogens

• prevents further blood loss

not good at other times:

• if clotting occurs in blood vessels, strokes heart attacks may occur

how does wound repair occur?

• following clotting, the clot dries out to form a scab

• epidermal cells below scab start to grow, sealing the wound permanently

• damaged blood vessels regrow

• collagen fibres are deposited to give the tissue strength

• once new epidermis reaches normal thickness, the scab sloughs off and the wound is healed