1. Immune system By the end of the lesson you should be able to
Outline the stages in phagocytosis.
Describe how antibodies work and how they are specific.

2. First lines of defense tears antibacterial enzymes
saliva antibacterial enzymes
mucus linings traps dirt and microbes
skin prevents entry
stomach acid low pH kills harmful microbes
“good” gut bacteria out compete bad

3. Pathogens = disease causing micro-organisms bacteria virus fungi,
protozoa,
parasite,
prion

4. Second lines of defence
Involves white blood cells
Non-specific response
invading pathogens are targeted by macrophages
Specific response
lymphocytes produce chemicals called antibodies that target specific pathogens

5. Phagocytes

6. Phagocytes Monocytes and macrophages
Provide a non-specific response to infection

7. Phagocytosis Stages in phagocytosis
Phagocyte detects chemicals released by a foreign intruder (e.g. bacteria)
Phagocyte moves up the concentration gradient towards the intruder
The phagocyte adheres to the foreign cell and engulfs it in a vacuole by an infolding of the cell membrane.
Lysosomes (organelles which are rich in digestive enzymes & found in the phagocytes cytoplasm) fuse with the vacuole & release their contents into it.

8. Phagocytosis
The bacterium is digested by the enzymes, and the breakdown products are absorbed by the phagocyte.
During infection, hundreds of phagocytes are needed.
Pus is dead bacteria and phagocytes!
link to phagocytosis

9. Lymphocyte

10. Lymphocytes Provide a specific immune response to infectious diseases.
There are 2 types: -
- T-cells B-cells
They produce antibodies.

11. Antigens all cells have surface markers called antigens.
body can recognise these as self or non-self (foreign)

12. Specific response Lymphocytes detect presence of foreign antigens
Stimulated to produce
specific proteins called
antibodies.

13. antibodies combine with their specific antigen (like a lock and key)
this renders the pathogen harmless.
= primary response

14. Immunity = the bodies ability to resist infection
can be natural or acquired

15. Immunological memory
after an infection is fought off some lymphocytes become memory cells.
if same pathogen returns memory cells stimulate the produce the specific antibody very rapidly.
the infection is fought off before symptoms appear = secondary response
vaccines can stimulate same response

16. Immune system Can you? Outline the stages in phagocytosis.
Describe how antibodies work and how they are specific.