Non-Specific Immunity

Initial response to foreign bodies
1. innate
2. responds non-specifically to any non-self bodies
3. rapid
Physical Barriers
1. Skin
  1. relatively thick, impermeable layer of epidermal cells (overlaying a rich vascular dermal layer).
    1. epidermal cells are produced at the base of the epidermis as basal cells and proliferate, moving outward.
      1. become flattened and die.
        dead cells contain keratin - forms a waterproof protective layer that reduces moisture loss and protects underlying tissues from microorganisms.
        tight junctions join epidermal cells which impede water loss and microbial penetration
  2. Secrete sebum and sweat
    1. low pH acidic secretions impair bacterial growth
2. Lungs
  1. bacteria trapped by stick mucous in the lining of the bronchi and bronchioles
3. Gut
  1. bacteria destroyed by acid secretions of the stomach
    1. 'chemical barriers'
Cytokines
1. interferons
  1. released from cells infected by viruses.
    1. bind to uninvaded cells, causing the production of inactive enzymes capable of break down viral mRNA, inhibiting protein synthesis.
      1. when viruses enter activated cells, viral-blocking enzymes are activated.
        virus is unable to multiply in newly invaded cells.
  2. stimulate other immune responses
2. interleukins
  1. secreted by macrophages and lympocytes
  2. regulate interactions between various parts of the immune system
3. special proteins secreted by various cells of the immune system when pathogens enter the tissues
Inflammation
1. characterised by redness, swelling or pain
2. pathogens invading tissues trigger an inflammatory response
  1. damaged cells release histamine, serotonin and other substances, which dilate blood vessels in the infected area.
    1. increased blood flow brings monocytes and neutrophils + plasma protein gamma gobulins (antibodies)
  2. capillary wall permeability increases leading to tissue oedema
3. sometimes the entire body is involved producing fever, or pyrexia
  1. thought to be caused by the neutrophils and macrophages releasing endogenous pyrogens (including prostaglandins)
    1. pyrogens travel to the hypothalamus, turning the thermostat up, increasing the body's temperature.
      1. directly affects bacterial metabolism
        optimum temp for bacteria is ~ 37 degrees i.e. normal body temp
      2. higher temperatures for prolonged periods can cause problems. denaturation of body proteins (esp. enzymes needed for biochemical reactions in body cells)
      3. mild fevers cause the spleen and liver to remove additional iron from blood. most disease causing bacteria require iron to reproduce
        fever decreases rate of bacterial replication and increases body's metabolism (facilitating healing and accelerating cellular defence mechanisms i.e. phagocytosis)
Phagocytosis
1. major function of inflammation is increased phagocytosis.
2. main phagocytotic leucocytes are monocytes and neutrophils
  1. monocytes leave circulation and transform into macrophages in tissues. can phagocytose ~100 bacteria before dying
    1. macrophages are widely distributed in the tissues but are particularly numerous in the gut wall and lungs.
    2. as part of the inflammatory process, they release interleukin-1.
  2. smaller neutrophils phagocytose ~20 bacteria before dying. Pus is largely formed of dead neutrophils
3. limited because if there is a high number of pathogenic microorganisms in the body, the normal blood flow rate is insufficient in bringing enough macrophages and neutrophils to the site of infection.
4. some bacteria (tuberculosis bacilli) can resist phagocytosis - protective cell walls/ proteins on the surface.

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	Criado por Erica Lai mais de 7 anos atrás