12.5 Non-specific Animal Defences Against Pathogens

Question 1

Examples of non-specific defences animals have as a barrier to pathogen entry

Answer 1

• the skin: prevents the entry of pathogens, the skin always produces sebum that inhibits the growth of pathogens
• mucous membranes: secrete sticky mucus. This traps microorganisms and contains lysozymes, which destroy bacterial and fungal cell walls. Mucus also contains phagocytes, which remove remaining pathogens
• lysozymes in tears and urine and the acid in the stomach also helps to prevent pathogens getting into our bodies
• we also have expulsive reflexes, coughs and sneezes eject pathogen mucus from the gas exchange system

Question 2

Blood clotting

Answer 2

A blood clot is a mesh of protein fibres that plug wounds to prevent pathogen entry and blood loss.
They’re formed by a series of chemical reactions that take place when platelets are exposed to damaged blood vessels.

Blood clot dries to form a scab and once wound is healed scab will fall off

Question 3

What is the inflammatory response?

Answer 3

• localised response to pathogens resulting in inflammation at the site of the wound
• inflammation causes redness, heat, pain and swelling of tissue
• Mast cells are activated in damaged tissue and release chemicals called histamines and cytokines
• histamines make the blood vessels dilate, causing localised heat and redness. The raised temperature helps prevent pathogens reproducing
• histamines make blood vessels leaky so blood plasma is forced out, forming tissue fluid. Tissue fluid causes swelling (oedema) and pain
• cytokines attract phagocytes to the site which dispose of pathogens by phagocytosis

Question 4

What are examples of non-specific defences that get rid of pathogens inside the body?

Answer 4

• fevers (cytokines stimulate hypothalamus to increase body temp, which inhibits pathogen reproduction (as pathogens reproduce best at 37°C) and specific immune system works faster at high temps)
• phagocytosis (phagocytes engulf and destroy pathogens)

Question 5

What are the stages of phagocytosis?

Answer 5

Phagocytes are specialised white blood cells that engulf and destroy pathogens.
There are two main type of phagocytes- neutrophils and macrophages
Phagocytes build up at the site of infection and attack pathogens.
Pus consists of dead neutrophils and pathogens.

Stages of phagocytosis (non-specific immune response):

1) Pathogens produce chemicals that attract phagocytes
2) phagocytes recognise non-self proteins on the pathogen
3) the phagocyte engulfs the pathogen and encloses it in a vacuole called a phagosome
4) the phagosome combines with a lysosome to form a phagolysosome
5) enzymes from the lysosome digest and destroy the pathogen

When a macrophage has digested a pathogen it combines with antigens from the pathogen surface membrane with glycoproteins in the cytoplasm to form the MHC (major histocompatibility complex). The MHC complex moves moves the pathogen antigens to the macrophages surface membrane, becoming an APC. These antigens now stimulated other cells involves in the specific immune system response

Question 6

Function of cytokines

Answer 6

Phagocytes that have engulfed a pathogen produce chemicals called cytokines.
Cytokines act as cell-signalling molecules informing other phagocytes that the body is under attack.

Question 7

Function of opsonins

Answer 7

Chemicals that bind to pathogens and ‘tag’ them so they are easily recognised by phagocytes
E.g. antibodies such as immunoglobulin G (IgG) and immunoglobulin M (IgM)