Topic 6 - Immunity, Infection and Forensics

• B Lymphocytes:

  • are formed and matured in bone marrow.
  • Aggregate in the lymph nodes and spleen
  • Different types (one for each antigen)
  • Each B cell has specific antigen receptors on the cell surface
• Non-specific response to infection is a response that is effective against a wide range of pathogens and doesn't involve recognising the pathogen. It doesn't react to specific antigens (although it is prompted by non-self antigens)
• The mouth is protected from infection by:

  • Lysozymes in the saliva which break down bacterial cell walls - causes the cell to burst
  • Hydrochloric stomach acid
  • Gut flora - bacteria which aid digestive processes and outcompete pathogenic bacteria for nutrients and space, secrete chemicals
• The nose is protected from infection by:

  • Mucus secreted by goblet cells which traps microbes and other particles, the mucus that's wafted up and out by the ciliated epithelium and the mucus that's swallowed gets broken down by stomach acid (along with the microbes present in the mucus)
  • Lysozyme in nasal secretions
• The ear is protected from infection by:

  • Bacteriocidal wax (bacteria killing wax)
• The eyes are protected from infection by:

  • Lysozymes in the tears
• The vagina is protected from infection by:

  • Its acidic pH which prevents the growth of bacteria
• The skin's keratin (a fibrous protein) outer layer is waxy and impermeable to water and pathogens.
• Blood clotting seals and protects wounds from infection. The phagocytes, attracted to the wound site by chemicals released by the damaged tissue, engulf and digest bacteria.
• Lysozyme is an antibacterial enzyme which kill bacteria by breaking down the cell wall by hydrolysis which causes the cell to burst
• Interferon is a type of cytokine which is produced by infected cells. It prevents viruses from attaching to uninfected host cells by binding to receptors - virus can't replicate because viruses can only replicate because viruses can only replicate inside host cells.
• Non-specific immune responses recognise the difference between self and non-self cells and react against anything that is non-self
• Antigens

  • chemicals on the surface of a cell such as proteins, glycoproteins or carbohydrates
  • Identify a cell as either 'self' or 'non-self'
• The role of the inflammatory response is to bring WBCs to the site of infection to dispose of bacteria by phagocytosis - the addition of (more) blood plasma to tissues makes it more difficult for pathogens to physically enter.
• How do forensic scientists estimate time of death?

  By establishing:

  • Extent of decomposition
  • Stage of succession
  • Forensic entomology
  • Body temperature of the deceased
  • The degree of muscle contraction
• What is decomposition carried out by?

  Decomposers e.g. bacteria and fungi
• What colour will the skin appear indicating the presence of decomposers?

  Green
• What does the breakdown of tissues and organs by microorganisms cause/produce?

  • Gases, such as methane, which lead to bloating
  • Blisters on the skin which fall off the body