Communicable Disease, Prevention and Immunity - Primary Non-specific Defences In Animals Flashcards
What are the primary non-specific defences in animals
- skin
- mucous membranes
- expulsive reflexes
- blood clotting
- wound repair
- inflammation
- fevers
What is skin
An organ which has an outer layer of dead cells containing the fibrous protein keratin
How does skin act as a defence
- acts as a physical barrier to pathogens
- skin flora of healthy microbes to compete with pathogens
- skin also produces sebum (only substance that inhibits growth of pathogens)
How do mucous membranes act as a defence
- protects body openings
- goblet cells in epithelium secrete mucus
- pathogens trapped
- ciliates epithelium in trachea, bronchi and bronchioles waft mucus upwards, where it is swallowed
What happens when the mucus is swallowed
Microbes killed by stomach acid
Give examples of expulsive reflexes
Coughs, sneezes, vomiting, diarrhoea
What are expulsive reflexes
Reflex responses which attempt to expel foreign objects, including pathogens, from the body
How are wounds sealed and why
Blood clots seal the wound to prevent the entry of microbes
As well as clotting factors, what else is released in wound repair
Seratonin
What is the role of seratonin in wound repair
Causes the walls of the blood vessels to contract, this reduces blood flow to the area
What happens once the clot is formed
It begins to dry out and form a scab
The scab shrinks as it dries, drawing the sides of the cut together, creating a temporary seal while the skin is repaired
What is the first stage of repairing the skin
Collagen is deposited under the scab
What then happens after the first stage of skin repair
- stem cells in the epidermis then undergo mitosis to form new cells
- new blood vessels grow to supply oxygen to the tissues
What happens once the new skin is complete
The scab will be released
What is inflammation characterised by
Pain, heat, redness and swelling of tissue
What kind of cell detects the presence of microbes in tissues
Mast cells
What do the mast cells release
- histamine
- cytokines
What is the main effect of histamine
Vasodilation, making capillary walls more permeable to white blood cells and some proteins
What does the vasodilation caused by histamine cause
An increase in tissue fluid, leading to swelling
What happens to the excess tissue fluid and why is this beneficial
Drains into the lymphatic system where there are many lymphocytes stored. This can result in pathogens meeting a lymphocyte, causing an immune response
What is the role of cytokines
Attract phagocytes to the area, which can remove pathogens by phagocytosis
Why does your temperature go up in a fever
Cytokines stimulate the hypothalamus to reset the body thermostat
Why is the high temperature of a fever beneficial
- higher temperatures inhibit pathogen reproduction
- immune system works faster at higher temperatures (eg cytotoxic T cells work better)
What do the many clotting factors involved in blood clotting initiate
An enzyme cascade
What is the first step of blood clotting
- Damage to blood vessel wall exposed collagen and releases clotting factors
- platelets bind to collagen and release clotting factors
- temporary platelet plug formed
What does the initial release of clotting factors cause
Inactive thromboplastin converted to active thromboplastin (enzyme)
What does active thromboplastin cause
Prothrombin activated to form thrombin (requires Ca2+ cofactor)
What does thrombin cause
Fibrinogen (soluble) converted to fibrin (insoluble mesh)
What does fibrin cause
- Fibres attach to platelets in plug
- Red blood cells and platelets trapped
- Clot forms
