(1) Defence Mechanism

• infection = an interaction between the pathogen and the body's various defence mechanism
• our body has several defence mechanisms against pathogens :

  • preventing entry
  • inflammation
  • recognising 'foreign' cells
• Defence Mechanism

  Preventing Entry :

  • prevent entry of pathogen
  • done through physical and chemical defences
• physical and chemical defence :

  • skin
  • mucous membrane
  • tears (containing the enzyme lysozymes which destroy bacteria)
  • saliva
• Defence Mechanism

  Inflammation :

  • inflammation in the region invaded by the pathogen
  • non-specific inflammatory response
• Defence Mechanism

  Recognising 'foreign cells' :

  • body recognises foreign cells
  • target any pathogen cell
  • known as specific immune response
• inflammation = swelling and heating
• tears contain the enzyme lysozyme, which destroys bacteria
• Defence mechanism is split into the non-specific response and the specific response
• Specific Response :

  • slower
  • specific to each pathogen
  • involves lymphocytes
• Non-specific :

  • immediate
  • same for all pathogens
  • involes phagocytes
• Non-specific response is split into :

  • physical barriers
  • phagocytosis
• specific response is split into :

  • cell mediated response
  • humoral response
• Physical barrier :

  • prevent entry of pathogen into the body
• Phagocytosis :

  • engulfing and destroying the pathogen
• Cell-mediated response :

  • involves T lymphocytes
• HUmoral Response :

  • involves B lymphocytes
• if a pathogen is to infect the body, it must gain entry
• the body's first line of defence is to form a physical or chemical barrier to entry
• the second line of defence is white blood cells
• there two main types of white blood cells :

  • phagocytes (non-specific)
  • lymphocytes (specific)
• Phagocytes :

  • white blood cells
  • continuously produced in the bone marrow
  • stored in bone marrow before being distributed around the body in the blood
• Phagocytes role :

  • remove dead cells
  • remove invasive microorganisms
  • carry out non-specific immune response
• phagocytosis is the process of a phagocyte engulfing and destroying a pathogen
• lysosomes are membrane bound organelles that contain digestive enzymes called lysozymes
• digestive enzymes = lysozymes
• lysozymes digest unwanted material present in the cell
• a phagocytic vacuole forms around the pathogen once it has been engulfed called a phagosome
• (1) Phagocytosis :

  • phagocyte is attracted by
  • chemical products of the pathogen (toxins) or
  • signals from a dying cell
  • they move along a concentration gradient
• (2) Phagocytosis :

  • receptors on phagocyte binds to PAMP - general feature of pathogens
• PAMP :

  phagocytes recognise and bind to

  • Pathogen Associated Molecular Pattern
• (3) Phagocytosis :

  • pathogen is engulfed
  • phagosome forms
• (4) Phagocytosis :

  • lysosomes fuse with the phagosome
  • release lysozymes
  • lysozymes break down the pathogen (hydrolyse )
• (5) Phagocytosis :

  • products of pathogen absorbed
• some phagocytes travel in the blood but can move out of the blood vessel into other tissues
• • chemical products of pathogens or dead, damaged and abnormal cells act as attractants, causing phagocytes to move towards the pathogen
  • phagocytes have several receptors on their cell-surface membrane that recognise, and attach to chemicals on the surface of the pathogen
  • they engulf the pathogen to form a vesicle, known as a phagosome
  • lysosmes move towards the vesicle and fuse with it
  • enzymes called lysozymes are present within the lysosome - (bacteria=hydrolyse cel wall)
  • the soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte