Defence Mechanisms.

FIRST LINE OF DEFENCE

Skin

• dry; composed of dead cells containing Keratin. Keratin cannot be digested easily, it is a barrier to pathogens; outer layer of cells are shed, taking bacteria with them. Microbes can only penetrate when surface is broken; shedding skin.
• Sebum (sebaceous glands) contain long chain fatty acids - lower the pH to acidic of 5.4 - inhibits growth of microorganisms and viruses.
• Sweat (sweat glands) - contains lysozyme - digests cell wall of bacteria.
• Tears - lysozyme and washing action.

  Gut

• Saliva - lysozyme; amylase (enzyme).
  HCL acid in stomach - destroys ingested bacteria
  Mechanical Flushing - due to movements of contents and fibre.

  Respiratory tract

• Mucus (goblet cells) - traps particle and microorganisms
• Cilia - sweeps mucus towards throat.

  Urinary / Reproductive tract
  

• Semen (male) - spermine - antibacterial
• Vagina - mucus membrane - acidic (lactic acid)
• Urethra - acidic due to acidic urine; washing action of urine.

SPECIFIC AND NON SPECIFIC RESPONSES

Non Specific:

Physical, chemical and cellular defences that prevent microbes from entering the body. (present from birth). A quick response system effective against a wide range of pathogens and foreign substances. (This system does not distinguish between different pathogens). It gives the same respone. 

Specific

(occurs when a particular antigen passes the body's passive defences.) It involves cells and proteins within the blood and lymph that attach, disarm, destroy and remove foreign bodies. (Highly effective, long lasting immunity against anything the body recognises as foreign) Responds to specific microorganisms and enhances the activity of the non-specific system.

WHY DOES YOUR BODY NOT ATTACK YOUR OWN CELLS?

When developing in the womb, the cells of the foetus constantly collide with pre-existing lymphocytes. Lymphocytes with proteins that fit the foetus' own cells die or are supressed. Only lymphocytes for foreign bodies remail. When a pathogen enters the body, it is likely that you will have a lymphocyte that recognises the pathogen.  What on the cell surface membrane would the lymphocyte recognise as foreign? The lymphocyte is able to do this because it will have a protein that is complementary to the pathogen protein. The lymphocyte is stimulated to…