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 micro-organisms  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  es/tterry/anim/phago053.html es/tterry/anim/phago053.html es/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: - - T-cells - B-cells They produce antibodies.

Antigens 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.

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