Defence mechanism

Question 1

How does infection occur?

Answer 1

An interaction between pathogen and the body’s defence mechanism.

Question 2

What is immunity?

Answer 2

When one is exposed from an infection but recovered from it and the body’s defenses become better prepared for the second infection which therefore can kill the pathogen before it causes any harm.

Question 3

What are the 2 types of defences?

Answer 3

• General and immediate defences e.g. skin forming barriers for the entry of pathogens and phagocytosis.
• The other defence is more specific, less rapid but longer lasting. These responses involve a type of white blood cell called a lymphocyte and there are 2 forms of lymphocyte.

Question 4

What are the 2 types of lymphocyte?

Answer 4

• Cell-mediated responses involve T-lymphocytes.

- Humoral responses involve B-lymphocytes.

Question 5

What must the lymphocytes need to be able to do before defend the body from invasions by foreign material?

Answer 5

Able to recognise the body’s own cells and molecules (self-cells) and those that are foreign (non-self).
They do this so the lymphocytes do not destroy the body’s own tissues.

Question 6

How are cells differentiated between self and non-self cells?

Answer 6

• They have specific molecules on their surface.
• These molecules can be a variety of types, the proteins have a highly specific tertiary structure and the variety of 3-D structures which allows the cells to be distinguished.

Question 7

What sort of cells do the proteins allow the immune system to detect?

Answer 7

• Pathogens e.g. HIV
• Non-self materials e.g. cells from other organisms of the same species
• Toxins that might be produced by certain pathogens e.g. bacterium that causes cholera
• Abnormal body cells e.g. cancer cells

Question 8

What’s the first stage or an immune response but why can it cause a problem for people that had tissue or organ transplants?

Answer 8

The first stage is to recognise all the non-self cells.
But if someone had a transplant, it would be recognised as non-self therefore it would try and destroy the implant.

To minimise the effect of tissue rejection, donor tissues for transplant are normally from close relatives so the matches are best genetically matched.
Immunosuppressant drugs can be given to reduce the level of the immune response.

Question 9

Do lymphocytes get produced due to an infection?

Answer 9

No, the specific lymphocytes already exist - 10 million different types.
Because there are so many different types, there’s a probability that the invaded pathogen would be complementary to one of the lymphocyte.

Question 10

Describe the defence mechanism.

Answer 10

Defence mechanism
- Non-specific *Response is immediate but the same to all pathogens e.g. physical barriers, phagocytosis
-Specific *Response is slower but specific to each pathogen. e.g. cell-mediated response from
T-lymphocyte or humoral response from B-lymphocyte.

Question 11

How do lymphocytes recognise cells belonging to the body?

Answer 11

• There are about 10 million different lymphocytes and each is capable of recognising the different chemical shape.
• In the fetus, lymphocytes are constantly colliding with other cells so they’ll collide with the body’s own cells.
• Some lymphocytes will have receptors that fit exactly with those self-cells, so those lymphocytes either die or suppressed.
• The only remaining lymphocytes are the ones that might fit with foreign materials, therefore, it only responds to them.
• In adults, lymphocytes are produced in the bone marrow and only encounter self-antigens. So any lymphocytes that show an immune response to these self-antigens will go through apoptosis (cell death) before they are differentiated into mature lymphocytes. No clones of those anti-self lymphocytes will appear in the blood so it leaves those that will only respond to non-self antigens.