12.5 Non-specific Animal Defences against Pathogens

Question 1

What are the 3 basic (non-specific defences) barriers mammals have against pathogens?

Answer 1

Skin
Body tracts
Lysozymes

Question 2

How does skin act as a barrier to pathogens?

Answer 2

Skin prevents entry of pathogens.
Skin has healthy microorganisms that outcompete pathogens for space on the body surface.
Skin produces sebum - oily substance which inhibits growth of pathogens.

Question 3

How do body tracts act as barriers to pathogens?

Answer 3

Many body tracts, including airways of gas exchange systems, are lined by mucous membranes that secrete sticky mucus.
Mucus traps microorganisms and contains lysozymes, which destroy bacterial and fungal cell walls.
Mucus contains phagocytes, which remove remaining pathogens.

Question 4

How do lysozymes in tears and urine act as barriers to pathogens?

Answer 4

The lysozymes and stomach acid help prevent pathogens entering the body.

Question 5

How do expulsive reflexes protect the body against pathogens? Give examples.

Answer 5

Coughing and sneezing - eject mucus containing pathogens from the gas exchange system

Vomiting and diarrhoea - expel contents of the gut along with any infective pathogens

Question 6

What happens when the skin is breached?

Answer 6

When the skin is open, pathogens can enter the body.
Blood clots rapidly to seal the wound.
When platelets come into contact with collagen in skin/ wall of damaged blood vessel, they adhere and begin secreting substances.

Question 7

What are the most important substances platelets release during blood clotting? Explain what their function is.

Answer 7

Thromboplastin - Enzyme that triggers reactions resulting in formation of a blood clot

Serotonin - Makes smooth muscle in walls of blood vessels contract. This narrows them and reduces blood supply to the area.

Question 8

Describe the stages of wound repair

Answer 8

Clot dries out, forming a hard scab which keeps pathogens out.
Epidermal cells below scab start to grow, permanently sealing the wound, while damaged blood vessels regrow.
Collagen fibres are deposited to give strength to the new tissue. Once new epidermis reaches normal thickness, the scab falls off and the wound is healed

Question 9

What is the inflammatory response?

Answer 9

A localised response to pathogens (also to damage and irritants) resulting in inflammation at the wound site.

Question 10

What is inflammation characterised by?

Answer 10

Pain, heat, redness, and swelling of tissue

Question 11

What type of cells are activated in the inflammatory response and what chemicals do they release?

Answer 11

Mast cells are activated in damaged tissue - release chemicals called histamines and cytokines

Question 12

What 2 things do histamines do? Explain the function of this.

Answer 12

1. Histamines dilate blood vessels - causing localised heat and redness.
   The raised temperature inhibits pathogen reproduction
2. Histamines make blood vessel walls more leaky - so blood plasma is forced out.
   Once blood plasma is forced out of blood, it’s known as tissue fluid.
   Tissue fluid causes swelling and pain.

Question 13

When does blood plasma turn into tissue fluid?

Answer 13

When it’s forced out of blood through blood vessel walls made leaky due to histamines.

Question 14

What does tissue fluid cause?

Answer 14

Swelling and pain

Question 15

What do cytokines do?

Answer 15

Attract white blood cells (phagocytes) to the site.

Phagocytes dispose of pathogens by phagocytosis.

Question 16

What is the second line of defence after pathogens enter the body?

Answer 16

Adaptations to prevent reproduction of pathogens / adaptations that kill pathogens.

Question 17

What is normal body temperature? What are of the brain is it controlled by?

Answer 17

37°C. Controlled by hypothalamus.

Question 18

What is the body’s response when pathogens invade the body?

Answer 18

Cytokines stimulate hypothalamus to raise body temperature.

Question 19

Why is it a useful adaptation to have cytokines stimulate the hypothalamus to raise the body temperature in response to a pathogen invasion? (2 reasons)

Answer 19

1. Most pathogens reproduce best at or below 37°C.
   Higher temperatures inhibit pathogen reproduction.
2. Specific immune system works faster at higher temperatures.

Question 20

What are phagocytes?

Answer 20

Specialised white blood cells.

Question 21

What do phagocytes do?

Answer 21

Engulf and destroy pathogens

Question 22

What are the 2 main types of phagocytes?

Answer 22

1. Neutrophils

2. Macrophages

Question 23

What do phagocytes do at the site of infection?

Answer 23

Build up

Question 24

What does pus consist of?

Answer 24

Dead neutrophils and pathogens

Question 25

What are the 5 stages of phagocytosis?

Answer 25

1. Pathogens produce chemicals that attract phagocytes
2. Phagocytes recognise non-human proteins on pathogen. This is a simple response to a non-self organism
3. The phagocyte engulfs the pathogen and encloses it in a vacuole, called a phagosome
4. Phagosome combines with a lysosome to form a phagolysosome
5. Enzymes from lysosome digest and destroy pathogen

Question 26

How do macrophages work?

Answer 26

When a macrophage digests a pathogen, the macrophage combines antigens from the pathogen surface membrane with the Major Histocompatability Complex (MHC) (glycoproteins in the cytoplasm).

MHC complex moves these pathogen antigens to the macrophage’s to the macrophage’s own surface membrane, becoming an antigen-presenting cell (APC).

These antigens stimulate other cells involved in the specific immune system response

Question 27

How long does it take a human neutrophil to engulf and destroy a bacterium?

Answer 27

10 minutes

Question 28

How do macrophages work?

Answer 28

When a macrophage digests a pathogen, the macrophage combines antigens from the pathogen surface membrane with special glycoproteins in the cytoplasm called the major histocompatibility complex (MHC).

MHC complex moves these pathogen antigens to the macrophage’s own surface membrane, becoming an antigen-presenting cell (APC).
These antigens now stimulate other cells involved in the specific immune system response.

Question 29

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Answer 29

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Question 33

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Question 34

What do phagocytes produce after engulfing a pathogen? What is the function of these chemicals?

Answer 34

Cytokines - Act as cell-signalling molecules.
Cytokines inform other phagocytes the body is under attack and stimulate them to move to the site of infection / inflammation.
Cytokines can increase body temperature and stimulate the specific immune response.

Question 35

Explain what Opsonins are. What is their function?

Answer 35

Chemicals that bind to pathogens and ‘tag’ them so they can be easily recognised by phagocytes.

Phagocytes have receptors on their membranes which bind to opsonins, and the phagocyte then engulfs the pathogen.

There are different opsonins, but antibodies e.g. immunoglobulin G and immunoglobulin M have the strongest effect.