C3.2 - primary defences and innate immunity (3p)

Question 1

what are pathogens?

Answer 1

a disease causing organisms

Question 2

what are the range of pathogens?

Answer 2

a broad range of disease-causing organisms can infect humans
- this includes viruses, bacteria, fungi and protists
- archaea are not known to cause any disease in humans

Question 3

how does the skin act as a primary defence against infection?

Answer 3

• never ciliated
• relatively thick and strong
• defends outer body surface
• produces fatty acids and lactic acid to kill pathogens
• surface cells tend to be dead

Question 4

how does the mucous membrane act as primary defences against infection?

Answer 4

• sometimes ciliated to move mucus away
• relatively thin and weak
• defends tubes leading to the outside
• produces mucus to trap pathogens
• surface cells tend to be alive

Question 5

what are the similarities between the mucous membrane and skin?

Answer 5

• they both act as physical and chemical barriers
• pathogens are able to penetrate through breaks

Question 6

why is blood clotting important?

Answer 6

blood clotting is important as it prevents pathogens from entering the body through damage to the skin

Question 7

what is the process of blood clotting as a primary defence?

Answer 7

1. platelets detect skin or blood vessel damage
2. platelets release clotting factors which start a chain or reactions (involving vitamins and proteins)
3. prothrombin is activated to thrombin (protease)
4. thrombin converts fibrinogen to fibrin
5. fibrin fibres form a mesh network that traps platelets and erythrocytes
6. clot forms and seals the wound

Question 8

what is fibrinogen?

Answer 8

fibrinogen is a soluble protein that is present in the blood plasma at all times

Question 9

what happens when it is converted into fibrin?

Answer 9

when it is converted to fibrin, it becomes insoluble

Question 10

what is the innate immune system?

Answer 10

the innate immune system responds to broad categories of pathogen, identified as non-self, and it does not change during an organisms’ life

Question 11

what cell types are involved in the innate immune system?

Answer 11

involves phagocytes:
- neutrophils - pathogen destruction
- macrophages - pathogen detection (links innate and adaptive immune system)

Question 12

what is the adaptive immune system?

Answer 12

the adaptive immune system responds in a specific way to particular pathogens via antibody production, and builds up a memory to make immune response more effective

Question 13

what cell types are involved in the adaptive immune system?

Answer 13

involves lymphocytes:
- helper t-cells - pathogen detection

B- cells
- plasma cells - antibody production
- memory cells - long-term immunity

Question 14

what is the process of phagocytosis?

Answer 14

1. phagocytes detect chemical signals released by pathogens
2. phagocytes leave the blood and use amoeboid movement to move to the site of infection
   - phagocytes squeeze between the capillary cells to leave the blood
3. phagocytes recognise pathogens by binding to them
4. phagocytes engulf and ingest the pathogen by endocytosis
   - the engulfed pathogens are held in a vesicle before being destroyed by enzymes and other chemicals within the cell
5. enzymes in the phagocyte’s lysosomes digest the pathogen