Defence mechanisms

Question 1

What is an infection?

Answer 1

An infection is an interaction between the pathogen and the body’s various defence mechanisms

Question 2

Millions of people die from infectious diseases but many also survive

For both of these scenarios, for an infected person, what happens inside the body involving the pathogen and the defence mechanisms?

Answer 2

When an individual dies from an infection, the pathogen has overwhelmed the defences which has caused the individual to pass

When the individual gets infected then recovers, this involves the defence mechanisms overwhelming the pathogen and the individual recovering from the disease

Question 3

When an individual’s defence mechanisms overcome the pathogen what does this result in?

Answer 3

When the body’s defence mechanisms overwhelm the pathogen, they become better prepared for a second infection from the same pathogen and can kill it before it can cause harm. This is known as immunity

Question 4

Why do some people get infected and seem unaffected by the infection?

Answer 4

This is caused by immunity. When an individual’s body mechanisms have become better prepared to kill a pathogen. Hence, when the person is infected by the same pathogen again it is prepared to quickly fight the infection.

Question 5

What type of person is rarely affected by an infection?

What type of people are more likely to be affected by infections?

Answer 5

A fit, healthy adult will rarely die to an infection

Those in ill health, the young and the elderly are usually more vulnerable to infections

Question 6

What are the two types of defence mechanisms?

Answer 6

There are specific and non specific defence mechanisms

Question 7

What are examples of specific defence mechanisms?

Answer 7

The cell mediated response, involving T lymphocytes

The humoral responses involving B lymphocytes

Question 8

What are examples of non specific defence mechanisms?

Answer 8

Phagocytosis

Physical barriers like your skin

Question 9

What must lymphocytes be able to do in order to defend the body?

Answer 9

Lymphocytes must be able to distinguish the body’s own cells and molecules (self cells) from those that are foreign (none - self cells)

Question 10

If lymphocytes could not distinguish between self and non - self cells, what would happen?

Answer 10

Lymphocytes would damage the organism’s own tissues

Question 11

What does each cell type have on it surface to identify it, whether non - self or self cells?

Answer 11

Non - self or self cells have antigen on their surface to allow you to identify it

Question 12

What are antigens? What is their function?

Answer 12

Antigens are macromolecules, often proteins, unique to each cell and pathogen. They signal to the immune system whether a cell is “foreign” or “self”.

Question 13

Why are the proteins (antigens) most important?

Answer 13

The proteins are important because proteins have enormous variety and a highly specific tertiary structure. This variety of 3D structures distinguish one cell from another

Question 14

What are four things these antigens allow your immune system to identify?

Answer 14

1) Pathogens (human immunodeficiency virus)

2) Non - self material (cells from other organisms of the same species)

3) Toxins (bacterium that causes cholera)

4) Abnormal body cells (cancer cells)

Question 15

Explain why tissue or organ transplants can be rejected by the recipient’s body?

Answer 15

When someone has had a tissue or organ transplant, the immune system recognises these as non - self even though they have come from individuals of the same species. this results in the immune system attempting to destroy the transplant.

Question 16

Describe two ways in which the risk of rejection can be minimise?

Answer 16

To minimise the effect of tissue rejection, donor tissues for transplant are normally matches as closely as possible to those of the recipient. In addition, immunosuppressant drugs are often administered to reduce the level of immune response that still occurs

Question 17

What happens to a lymphocyte when it has complementary proteins (antibodies) to a pathogen within the body?

Answer 17

When an infection occurs, the type of lymphocyte that has the complementary proteins to those of the pathogen is stimulated to divide to build up its numbers to a level where is can effectively destroy it.

This is known as clonal selection

Question 18

How do lymphocytes recognise cells belonging to the body, when individuals are in the stage of early development?

Answer 18

During early development, lymphocytes are exposed to the body’s own cells. Any lymphocyte that responds to the body’s own antigens is either destroyed or suppressed

Question 19

What is clonal deletion and what does it allow?

Answer 19

Clonal deletion is a process in the immune system that removes T and B lymphocytes that attack the body’s own cells.

This ensures remaining lymphocytes are tolerant to self antigen and do not attack the body’s own tissues

Question 20

What occurs if clonal deletion does not occur properly?

Answer 20

If clonal deletion does not occur properly, lymphocytes which attack self - cells are produced, causing the symptoms of autoimmune diseases