The Immune System.

PRIMARY DEFENCES

Skin - physical barrier that blocks pathogens from entering the body. Also acts as a chemical barrier by producing anti-microbial chemicals and can lower 'p' 'H' inhibiting pathogen growth.

Mucus Membrane - protect body openings that are exposed to the environment. Some secrete mucus which traps the pathogens.

THE IMMUNE RESPONSE SYSTEM

Stage 1 - Phagocytes engulf pathogens:

• The white blood cell recognises the antigens on the pathogen.
• The cytoplasm moves around the pathogen engulfing it.
• The pathogen is now inside a Phagocytic Vacuole, a lysosome fuses with it and the digestive enzymes break down the pathogen.
• The antigens from the pathogen are then presented by the phagocyte on its cell surface which triggers ...

Stage 2 - 'T' Lymphocytes are activated by the Phagocytes:

• The receptors present on the lymphocyte bind to the antigens on the phagocyte cell membrane.
• Each 'T' Lymphocyte has a different shaped receptor.
• When a receptor meets an antigen with a complimentary shape it binds to it so each 'T' Lymphocyte binds to a different antigen.
• The 'T' Lymphocyte then activates - it divides and differentiates into different types of 'T' Lymphocyte, some release substances to activate 'B' Lymphocytes. Some 'T' Lymphocytes kill the pathogen. Some 'T' Lymphocytes become memory cells this leads to ...

Stage 3 - 'B' Lymphocytes are activated by the chemicals released from the 'T' Lymphocytes:

• 'B' Lymphocytes are covered with antibodies made of protein.
• Antibodies bind to the…