Non-Specific Animal Defences 12.5

Question 1

Different animal defences

Answer 1

The primary response is non-specific and acts very quickly whereas the immune system is specific to certain pathogens and takes longer to act.

Question 2

How are pathogens kept out of the body?

Answer 2

• The skin covers the body and creates a barrier so pathogens cannot enter. It also has flora which are healthy microorganisms that will compete with the pathogens for space, it also has oily sebum that traps bacteria.
• The airways are lined with goblet cells and mucus membranes that release mucus and trap pathogens and bacteria so they cannot enter the lungs.
• Lysozymes in tears and urine and stomach prevent the pathogens getting in the body.
• We also have reflexes that eliminate pathogens like sneezing and coughing to release pathogens in the airway, or diarrhoea which eliminates them out of the digestive system.

Question 3

Wound repair

Answer 3

If you cut yourself, you’re now exposed to pathogens entering your body. Platelets will come into contact with your collagen fibres from the damaged skin and also the or the damaged blood vessel and they will adhere and secrete substances. These substances are thromboplastin which triggers a cascade of reactions to form a blood clot and also serotonin which makes the muscle wall contract to reduce blood flow near the wound, so you don’t lose a lot of blood. Your clot will then dry up to form a scab, your epithelial cells will start to grow under it along with your blood vessels. Collagen will grow to give tissue strength. Once the skin is the right thickness, the scab will fall off.

Question 4

Inflammatory response

Answer 4

This is the response to pathogens at the site of a wound. It is characterised by pain, redness, swelling etc.. Mast cells in connective tissue are activated if the tissue is damaged and they release cytokines and histamines. Sometimes if the infection is widespread it will cause a whole body rash.

Question 5

Histamines

Answer 5

This dilates the blood vessels so more blood flows through, it increases the heat and redness. The heat is so pathogens cannot reproduce and die. It also makes blood vessels more leaky so more tissue fluid is forced out of the blood vessels and this causes swelling or oedema and pain.

Question 6

Cytokines

Answer 6

These will attract white blood cells called phagocytes so that the pathogens can be destroyed by phagocytosis.

Question 7

Why do we get fevers?

Answer 7

Normally, the body is 37 degrees, however when a pathogen invades your body, cytokines will trigger your hypothalamus to increase your body temperature. This is to inhibit pathogen reproduction and denature them and also the immune system works faster at higher temperature.

Question 8

Phagocytes

Answer 8

These are specialised white blood cells that make up part of your immune system and can engulf and destroy pathogens. These include neutrophils and macrophages.

Question 9

Neutrophils

Answer 9

These make up 70% of white blood cells. They have a multilobed nucleus so they can squeeze through small places and engulf pathogens quickly.

Question 10

Macrophages

Answer 10

They have a round nucleus and make up 4% of white blood cells. They are involved in the specific and non-specific defence.

Question 11

Phagocytosis

Answer 11

Phagocytes will always build up at the site of an infection and attack the pathogens. If you have pus in a wound, these are dead neutrophils and pathogens.

• Pathogens will release chemicals that will attract phagocytes to it.
• The phagocyte will approach the pathogen and recognise that the pathogen is non-self by binding to its antigens
• The phagocyte will then engulf the pathogen and surround it by a vacuole and it will become a phagosome.
• Now there are lysosomes that combine with the phagosome to produce a phagolysosome.
• The pathogen will be broken down by hydrolytic enzymes in the lysosome and so will be destroyed.
• Neutrophils can do this in 10 minutes

Question 12

What happens in phagocytosis in a macrophage?

Answer 12

After the pathogen has been broken down, the pathogens antigens will combine with glycoproteins in the cytoplasm called MHC or major histocompatibility complex. The MHC complex will moves the antigens of the pathogen to the macrophages cell surface membrane and it will now become an antigen presenting cell or APC. These can stimulate other cells in the specific immune response.

Question 13

Helpful chemicals

Answer 13

Phagocytes that have engulfed pathogens will produce cytokines and these are important for increasing body temperature and also as cell signalling because they can send alarm signals to other phagocytes and attract them.
Opsonins are chemicals that bind to the pathogens and act as a tag so they are more easily recognised by phagocytes. The phagocytes will bind to common opsonins from their receptors and that will help to engulf the pathogen.