12.5 Non-specific Animal Defences Against Pathogens

Question 1

What are primary defences?

Answer 1

Barriers that prevent pathogens from entering the body

Question 2

Examples of primary defences:

Answer 2

• skin
• naturally living flora on the skin that outcompetes pathogens
• conjunctiva (membrane covering the eye)
• lysozymes in tears
• mucus in airways
• ciliated epithelial cells in airways
• mucus and acidic conditions in stomach and vagina

Question 3

How are primary defences repaired when damaged?

Answer 3

Blood clotting and wound repair

Question 4

What is the process of blood clotting?

Answer 4

1. Damaged tissue
2. Platelets activates by damaged tissue
3. Thromboplastin is released
4. Thromboplastin catalyses the reaction between Ca2+ ions and prothrombin to produce thrombin
5. Thrombin then catalyses the conversion of fibrinogen to fibrin
6. Fibrin forms a clot

Question 5

What are secondary defences?

Answer 5

Pathogens can evade primary defences and infect an animal

Infections trigger internal non-specific responses: inflammation, fevers and phagocytosis

Question 6

What happens in wound repair?

Answer 6

Serotonin is released which makes the smooth muscle in the walls of blood vessels contract, so they narrow and reduce the supply of blood to the damaged area

Question 7

What is the process of inflammation?

Answer 7

• Mast cells (which are leucocytes) release histamines
• Histamines dilates blood vessels
• The dilation of blood vessels cause more plasma to move into tissue fluid
• This raises temperature and causes swelling and pain
• Cytokines attract phagocytes to the site
• The pathogens are removed via phagocytosis

Question 8

How does inflammation help?

Answer 8

It reduces the rate of pathogen reproduction

Question 9

What is the process of phagocytosis?

Answer 9

1. The pathogen releases chemicals that attract phagocyte
2. Phagocytes recognise the non-human proteins on the pathogen. This is not a response to a specific pathogen, but simply a cell or organism that is non-self
3. The phagocyte engulfs the pathogen and the pathogen is enclosed in a vacuole (called a phagosome)
4. Lysosome fuses with phagosome (forming a phagolysosome)
5. Enzymes released by the lysosomes digest and destroy the pathogen

Question 10

How does phagocytosis help?

Answer 10

It destroys pathogenic cells

Question 11

What is the process of a fever

Answer 11

1. Normal body temperature is around 37°C and is maintained by the hypothalamus
2. When pathogens enter the body, cytokines stimulate the hypothalamus to reset the body’s thermostat and the temperature goes up

Question 12

What are expulsive reflexes?

Answer 12

Ways in which the body expels pathogens
E.g.
- coughs and sneezes eject pathogen-laden mucus from the gas exchange system
- vomiting and diarrhoea expel the content of the gut along with any infective pathogens

Question 13

What is the role of collagen in wound repair?

Answer 13

It strengthens the new cells that form