1. The Immune System

2. The immune system
Infectious diseases: diseases that can be spread by contact with infected people, animals, water or food
Pathogen: an organism or substance that can cause a disease

3. The immune system
Immune system: body system that defends against pathogens

4. The first line of defence
Skin is a physical barrier - stops pathogens from entering the body
Sweat & oils on skin are slightly acidic
Gastric juices in the stomach can destroy some pathogens
Mucus & cilia in the nose stop pathogens from entering the respiratory system

5. Unfortunately, pathogens still get into our body …

6. Second line of defence
If a pathogen gets past the first line of defence
Includes two types of immune response:
Innate Immune Response: response you are born with.
Acquired Immune Response: specific attack on a pathogen.

7. Innate Immune Response
Quick & general, responds the same to any invader
Two steps
Flow of fluid into site of infection
Causes fever, swelling, and redness in area
Swelling and redness = inflammation
Increase in the types of white blood cells called phagocytes
Phagocytes destroy pathogens.

8. Acquired immune response
A.K.A tertiary defence system
Very specific attack on pathogen or antigen
Antigen = non-living particle or substance the body cannot recognize
All acquired immune responses give you active immunity
Active immunity: long lasting protection against a pathogen

9. Acquired immune response
First step in acquired immune response:
B cells: recognize antigens present in the body.
Produce particles, called antibodies, used to fight antigens.

10. Acquired immune response
Second step in the acquired immune response:
Two types of T cells:
Helper T cells: recognize antigen or pathogen and activate B cells
Killer T cells: recognize & destroy antigen or pathogen without B cells.