12.5 – Non-specific animal defences against Pathogens

Question 1

What are the body’s barrier to pathogen entry?

Answer 1

• Skin, covers and protects entry of pathogens, skin flora of healthy microorganisms that outcompete pathogen for space.
• Skin produces sebum, oily substance that inhibits pathogen growth
• Body tracts of gas exchange system lined with mucus membranes – secrete mucus, traps microorganisms, contains lysozymes (destroy bacterial & fungal cell walls)
• Lysozymes in tears and urine, acid in stomach, prevents pathogens entering the body.

Question 2

How does blood clotting and wound repair work initially?

Answer 2

• Blood clot seals an opening in the skin that would otherwise allow pathogens in
• Platelets come into contact with collagen of skin, or wall of damaged blood vessels, they adhere and secrete substances:

Question 3

State the roles of thromboplastin and serotonin in blood clotting and wound repair.

Answer 3

Thromboplastin: enzyme triggering reactions that form a blood clot

Serotonin: makes smooth muscles in blood vessels contract, reducing blood supply to the area

Question 4

Describe the process of blood clotting and wound repair (detail).

Answer 4

1. Clot dries, forming hard outer shell of scab, keeping pathogens out
2. Epidermal cells below start to grow, sealing wound permanently, whilst damaged blood vessels regrow
3. Collagen fibres deposited to give new tissue strength.
4. Scab is removed once epidermis reaches normal thickness

Question 5

What is the inflammatory response?

Answer 5

• Localised response to pathogens resulting in inflammation (biological response of vascular tissue)
• Mast cells (cell filled with basophil granules) activated in damaged tissue – releases histamines and cytokines

Question 6

What is the role of:

Histamines

Cytokines

Answer 6

Histamines: causes vasodilation, causing localised heat and redness. Raised temperature helps prevent pathogenic reproduction

Histamines also make blood vessels leak more forcing blood plasma out (tissue fluid). The swelling caused by tissue fluid is called oedema, causes pain too

Cytokines: attract white blood cells phagocytes) to the site. They dispose pathogens by phagocytosis

Question 7

What is the purpose of fevers?

Answer 7

• Normal body temperature, 37⁰C, maintained by hypothalamus in brain, when pathogens invade, hypothalamus signals an increase in temperature
• This adaptation is because, pathogens reproduce best at 37^oC or lower, therefore higher temperature’s inhibits reproduction
• Specific immune system is faster at higher temperatures

Question 8

What are phagocytes and their types?

Answer 8

Phagocytes – specialised white cells, they engulf and destroy pathogens.

Two types: neutrophils (multi lobed nucleus), macrophages (circular nucleus)

• Phagocytes build up at site of infection to attack pathogens, pus in a spot, cut or wound consists of dead neutrophils and pathogens.

Question 9

State the process of phagocytosis.

Answer 9

1. Pathogens produce chemicals attracting phagocytes
2. Phagocytes recognise non-human proteins on pathogen (as foreign) and binds to it. Not a specific response to a pathogen, just a general response to cells that are non-self.
3. Phagocyte engulfs pathogen in a vacuole called phagosome (endocytosis)
4. Phagosome combines with lysosome to form phagolysosome
5. Lytic enzymes in phagolysosome digest and destroy pathogen.
6. Neutrophils take 10 minutes to engulf and destroy bacterium, macrophages take longer as, antigens from pathogen surface membrane with combines with special glycoprotein MHC (major histocompatibility complex).
7. MHC complex moves pathogen’s antigens to macrophage’s cell surface membrane, becoming an APC (antigen presenting cell)
8. The antigens on the surface stimulate other cells involved in specific immune response

Question 10

What do phagocytes that engulf pathogens do?

Answer 10

• Phagocytes that engulf pathogens produce cytokines – act as cell signalling molecules, informing other molecules the body is under attack, stimulating them to move to site of infection. They also increase body temperature and stimulate specific response

Question 11

What are the roles of opsonins?

Answer 11

• Opsonins – chemicals that bind to pathogens and tag them, this makes them more recognisable to phagocytes,
• Phagocytes have opsonin receptors, phagocyte then engulfs the pathogen.
• There are many opsonin types – antibodies such as immunoglobulin G (IgG) and immunoglobulin M (IgM) have greatest effect.

Question 12

Describe the cascade of reactions leading to a blood clot.

Answer 12

Platelets release thromboplastin

Thromboplastic and Ca²⁺ catalyse the reaction converting prothrombin to thrombin

Thrombin catalyses the conversion of fibrinogen to fibrin to form a clot