immune system

immune system - Transcript

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.
First lines of defence
skin prevents entry
tears              
antibacterial          
     enzymes
saliva 
antibacterial          
     enzymes
stomach acid       
       low pH kills 
harmful microbes
mucus linings traps 
dirt and microbes
“good” gut
bacteria out 
compete bad
Pathogens
 = disease causing micro­organisms
 bacteria
 virus
 fungi, 
 protozoa, 
 parasite, 
 prion
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
Phagocytes
Phagocytes
 Monocytes and macrophages
 Provide a non-specific response to infection
 http://www.microbelibrary.org/images/tterry/anim/phago053.html
Phagocytosis
 Stages in phagocytosis
1. Phagocyte detects chemicals released by a foreign intruder 
(e.g. bacteria)
2. Phagocyte moves up the concentration gradient towards 
the intruder
3. The phagocyte adheres to the foreign cell and engulfs it in 
a vacuole by an infolding of the cell membrane.
4. Lysosomes (organelles which are rich in digestive enzymes 
& found in the phagocytes cytoplasm) fuse with the 
vacuole & release their contents into it.
Phagocytosis
5. 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
Pus
An accumulation of : ­
 dead phagocytes
 destroyed bacteria
 dead cells
Lymphocyte
Lymphocytes
Provide a specific immune response to
infectious diseases.
There are 2 types: ­
­ T­cells 
­ B­cells
They produce antibodies.
Antigens
 all cells have surface 
markers called 
antigens.
 body can recognise these 
as self or non-self 
(foreign)
Specific response
 Lymphocytes detect presence of foreign antigens
 Stimulated to produce 
   specific proteins called 
   antibodies.
 antibodies combine with their specific antigen (like a 
lock and key)
 this renders the pathogen harmless.
 = primary response
Immunity
  =  the bodies ability to resist infection
 can be natural or acquired
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
Immune system
Can you
 Outline the stages in phagocytosis.
 Describe how antibodies work and how they are 
specific.