3.2.5 The Defensive Functions of Mammalian Blood Flashcards
What is an antigen?
Molecules (usually proteins) that stimulates an immune response when detected by body
Describe how lymphocytes recognise self from non-self
- Each lymphocyte recognises a different chemical shape
- They collide with body’s own material (self)
- Some lymphocytes have receptors that fit body’s cells
- These either die or are suppressed
- Remaining fit only foreign material
Name the 4 main stages of immune response
- Phagocytosis
- Phagocytes Activate T-cells
- T-cells Activate B-cells, which divide into Plasma cells
- Plasma cells make more Antibodies to a Specific Antigen
Where are phagocytes found?
In blood and tissues
Describe phagocytosis (5)
- Phagocyte recognises (foreign) antigen
- Phagocyte engulfs pathogen
- Enclosed in vacuole/phagosome
- (Vacuole) fuses with lysosome
- Lysosome contains enzymes (lysozymes) that hydrolyse pathogen
Why does phagocytes moves towards pathogens?
∵ they’re attracted to pathogen’s chemical products
Phagocytes engulf pathogens by _____
endocytosis
Waste products removed by _____
exocytosis
How do lysozymes break down bacteria?
Hydrolyse the cell walls of bacteria
What do phagocytes do at the end of phagocytosis?
Phagocyte presents pathogen’s antigens on its surface to activate other immune system cells
What do T-cells only respond to?
Antigen-presenting cells
Where do T-cells (aka T-lymphocyte) mature?
In thymus gland
Describe what T-cells do
- Respond to antigens on foreign and infected cells
- Specific receptors on helper T cells bind to specific antigen presented by phagocytes (antigen-presenting cell)
- This activates T-cell: Binding triggers rapid mitosis = T cells are cloned
Name 4 things that the cloned helper T-cells do
- Activate cytotoxic T cells
- Activate B-cells to divide and secrete their antibodies
- Develop into memory cells
- Release chemical signals that activate and stimulate phagocytes
Describe how cytotoxic T-cells kill infected cells
- Produce protein called perforin that makes holes in cell-surface membrane
- Holes means cell membrane becomes freely permeable
- Control of substances no longer controls and cell dies
Why is the action of T-cells most effective against viruses?
∵ they replicate inside cells, sacrificing these body cells prevents viruses from multiplying and infecting more cells
What is the role of macrophages in stimulating B lymphocytes?
- Antigen in membrane presented to lymphocytes
- Produce cytokinins
What are B-cells (B-lymphocytes)?
White blood cell that’s covered with antibodies
What are antibodies?
- Proteins that bind antigens to form antigen-antibody complex
- Stimulate immune response
Describe how T-cells activate B-cells, which divide into plasma cells
- When antibody on surface of B-cells meets complementary shaped antigen = binds to it
- This, together with chemicals released from helper T-cells, activates B-cell = divides by mitosis
- Clonal selection: form clones/produce plasma cells
- Make antibodies
- Plasma cells produce memory cells
What do plasma cells do?
Secrete loads of antibodies specific to antigen
callled monoclonal antibodies
Describe what antibodies do to destroy pathogens
- Antibody has 2 binding sites = can bind 2 pathogens at same time
- Means pathogens & antibodies become clumped together = called agglutination
- Phagocytes bind to antibodies and phagocytose many pathogens at once
- Process leads to destruction of pathogens carrying this antigen in body
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