Pathogens = microorganisms that cause disease

• Bacteria

• Fungi

• Viruses

  They cause disease by:

  • Damaging host cells or releasing toxins

Antigens = specific molecules on the surface of cells which are used in cell recognition.

Antigens are proteins on cell membranes which cause an immune response

Antigens are specific to each type of cells within the organism.

• Immune system can identify both foreign and non-self-antigens

  Antigens allow the immune system to detect:

  • Pathogens

  • Cells from other organisms

  • Abnormal body cells

  • Toxins

Immune System

• Responsible for preventing infectious diseases

• Two types = Non-specific and Specific Immune System

• Non specific = from birth is is effective against a wide range of pathogens and foreign substances

• Specific = slow and only effective against specific pathogens but response is faster after re-infection

Non-Specific Defence

1) Physical Barriers

• Protective Covering

• Ciliated epithelia covered in the mucus

• Hydrochloric Acid in the stomach

• Tears are salty and contain lysozymes

2) Phagocytosis - first stage of the immune response

• phagocyte engulfs a foreign substance within a vesicle and digests it

1 - A phagocyte recognises the antigens on a pathogen is foreign

2 - The cytoplasm moves around the pathogen, engulfing it (endocytosis)

3 - The pathogen is now contained in a phagocytic vacuole (phagosome)

4 - A lysosome fuses with the phagosome and released it lysozymes

5 - The lysosomes hydrolyse the pathogen and soluble products are absorbed into the cytoplasm

6 - The phagocyte displays the antigens from the pathogen on its cell membrane - it is now an antigen-presenting cell.

Specific Immune Response

1 - The Cellular Response

• T lymphocytes carry out the cellular response as they recognise the non-self-antigens on the surface of other body cells

• T cells have slightly different receptors that are only activated with the complementary antigen which has entered the body

1 - Antigen-presenting cell was produced in phagocytosis

2 - Receptors on specific T cells fit exactly with the antigens

3 - This then activates the T cells to rapidly divide by mitosis and form genetically identical cells

4 - These T cells have 3 different types with different functions:

• Cytotoxic Cells - destroy infected body cells

• Memory T cells - enable rapid response to future infections by the same pathogen

• Helper T cells - enable chemical signals to stimulate other cells in the immune system like phagocytes, B cells and Tc cells.

ETC. TBA