12.5 - Non Specfic Animal Defences Against Pathogens

Question 1

What is the first line of defence ?

Answer 1

Prevents the entry of pathogens and is compromised of :
- skin
- mucous membranes
- expulsive reflexes
- chemical secretions

Question 2

How does the skin act as a barrier ?

Answer 2

• possesses an outer layer of dry, hardened cells filled with keratin
• keratin is a tough fibrous protein
• these layer of cells act as a physical barrier to pathogens
• there are secretions of sebum that contain fatty acids which have antimicrobial properties
• evaporation of sweat from the skin leaves behind a salt residue
• lack of moisture , low pH and high salinity creates an inhospitable environment for the growth of microorganisms

Question 3

How do mucous membranes act as a barrier ?

Answer 3

• mucous membranes line the gut, airways and reproductive system
• contains epithelial cells and mucus-secreting cells eg. Goblet cells
• mucus contains lots of glycoproteins with long carbohydrate chains —> these chains make mucus sticky
• viruses, bacteria , pollen and dust float about in the air that we breathe in
• mucus In the airways can trap these particles
• the particles are then moved towards the back of the throat by cilia

Question 4

How do expulsive reflexes act as a barrier ?

Answer 4

• when a pathogen irritates the lining of an airway it can trigger an expulsive reflex eg. A cough or sneeze
• both a cough and sneeze result in a sudden expulsion of air
• this expelled air contains secretions from the respiratory tract along with the foreign particles that have entered

Question 5

How do chemical secretions act as a barrier ?

Answer 5

• lysozymes are antimicrobial enzymes that breakdown the cell wall of bacteria
• they are found in body fluids eg. Blood,tears,sweat and breast milk
• Hydrochloric acid is produced by the cops that line the stomach
• the acid creates a low pH inside the stomach which helps to kill any bacteria that has been ingested alongside food
• the cells of the gut secret mucus to prevent being damaged by HCl

Question 6

What are commensalism microorganisms?

Answer 6

• on average 1kg of a humans weight is made up of the bacteria on or inside their body
• Candida albicans and E.coli are examples of bacteria commonly found on and in humans
• these microorganisms grow on the skin , in the mouth and intestines however they do not cause disease
• their growth is limited by the defence mechanisms
• ousting these microorganisms can have a major benefit for humans
• they compete with pathogenic microorganisms and prevent them from invading host tissue
• antibiotics often kill friendly gut bacteria which can allow for opportunistic pathogens to grow

Question 7

What happens when blood clots ?

Answer 7

• if you cut your self the skin is breached and pathogens can enter the body
• blood clots rapidly to seal the wound
• when platelets come into contact with collagen in skin or the wall of the damaged blood vessel they adhere and begin secreting several substances

Question 8

What is thromboplastin ?

Answer 8

an enzyme that triggers a cascade of reactions resulting in the formation of a blood clot

Question 9

What is serotonin ?

Answer 9

which makes the smooth muscle in the walls of the blood vessels contract so they narrow and reduce the supply of blood to the area

Question 10

What happens when the clot dries out ?

Answer 10

• clot dries = forming a hard,tough scab that keeps pathogens out
• epidermal cells below the scab start to grow , sealing the wound permanently while damaged blood vessels regrow
• collagen fibres are deposited to give the new tissue strength
• once the new epidermis reaches normal thickness the scab sloughs off and the wound is healed

Question 11

What is inflammation ?

Answer 11

The surrounding area of a wound can sometimes become swollen , warm and painful to touch this is described as inflammation

Question 12

What is inflammation characterised by ?

Answer 12

Pain
Heat
Redness
Swelling of tissue

Question 13

What does inflammation occur via ?

Answer 13

• a chemical signalling molecule which cause the migration of phagocytes into the tissue and increased blood flow
• it is a local response to infection and tissue damage

Question 14

What are mast cells ?

Answer 14

• are activated in damaged tissue by secreting the cell signalling molecule histamine

Question 15

What does histamine stimulate ?

Answer 15

• vasodilation increases blood flow through capillaries
• “leaky” capillaries allow fluid to enter the tissue and Create swelling
• a portion of the plasma proteins leave the blood
• phagocytes leave the blood and enter the tissue to engulf foreign particles
• cells release cytokines that trigger an immune response to the infected area

Question 16

What part do cytokines play in this process ?

Answer 16

• cytokines are cell signalling compounds that stimulate inflammation and an immune response
• they are small proteins
• interleukins are a group call of cytokines
• interleukin 1 and interleukin 6 promote inflammation
• IL-1 targets the brain , causing drowsiness and fever

Question 17

Explain the wound repair process

Answer 17

• underneath the scab there are stem cells that divide by mitosis to heal the wound

1. New blood vessels form
2. Collagen is produced
3. Granulation tissue forms to fill the wound
4. Stem cells move over the new tissue and divide to produce epithelial cells
5. Contractile cells cause wound contraction
6. Unwanted cells die

Question 18

What is the second line of defence ?

Answer 18

Adaptations to prevent them frowning or to destroy them

Question 19

What is the normal body temperature ?

Answer 19

37°

Question 20

What is the temp maintained by ?

Answer 20

The hypothalamus in the brain

Question 21

What occurs when a pathogen invades your body , how do the cytokines act accordingly?

Answer 21

Cytokines stimulate your hypothalamus to reset the thermostat and your temperature goes up

Question 22

In relevance to the prior question , how is this a useful adaptation ?

Answer 22

• most pathogens reproduce best at or below 37°C —> higher temperatures inhibit pathogen reproduction
• the specific immune system works faster at high temperatures

Question 23

What are phagocytes ?

Answer 23

Specialised white cells that engulf and destroy pathogens

Question 24

What are the two main types of phagocytes ?

Answer 24

Neutrophils & macrophages

Question 25

What does pus contain ?

Answer 25

Dead neutrophils and pathogens

Question 26

What are the stages of phagocytosis ?

Answer 26

1. Pathogens produce chemicals that attract phagocytes
2. Phagocytes recognise non-human proteins on the pathogen , this is a response not to a specific type of pathogen but simply a cell or organism that is non self
3. The phagocyte engulfs the pathogen and enclosed 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

Question 27

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

Answer 27

10 minutes

Question 28

What occurs when a macrophage has digested a pathogen ?

Answer 28

• combines with antigens from the pathogen surface membrane with special glycoproteins in the cytoplasm called the MAJOR HISTOCOMPATIBILITY COMPLEX ( MHC)
• the MHC complex moves these pathogen antigens to the macrophages own surface membrane becoming an antigen presenting cell (APC)
• these antigens now stimulate other cells involved in the specific immune system response

Question 29

What are opsonins ?

Answer 29

• chemicals that bind to pathogens and tag them so they can be more easily recognised by phagocytes
• phagocytes have receptors on their cell membranes that bind to common opsonins and the phagocyte then engulfs the pathogen

Question 30

What type of opsonins have the strongest effect ?

Answer 30

Immunoglobulin G ( IgG)

Immunoglobulin M ( IgM)