Defence mechanisms

Question 1

What is an infection?

Answer 1

An interaction between the pathogen + the body’s various defence mechanisms

Question 2

What is immunity?

Answer 2

The body is protected from a disease - the pathogen is killed before it can cause any harm

Question 3

Name the two types of specific responses?

Answer 3

• Cell-mediated response (by T lymphocytes)

* Humoral responses (by B lymphocytes)

Question 4

How do specific responses occur?

Answer 4

• Response is slower

* Specific to each pathogen

Question 5

What would happen if lymphocytes couldn’t distinguish the own body cells from those that are foreign?

Answer 5

The lymphocytes would destroy the organism’s own tissues

Question 6

What do all cells have on their surface to identify cells + pathogens?

Answer 6

Protein molecules that have a highly specific (3D) tertiary structure

Question 7

What do the specific proteins on the surface of cells allow the immune system to identify?

Answer 7

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

Question 8

How do you minimise the effect of tissue rejection?

Answer 8

• Donor tissues for transplant are normally matched as closely as possible to those of the recipient - best matches often come from relatives that are genetically close
• Immunosuppressant drugs are often administered to reduce the level of the immune response that still occurs

Question 9

Specific lymphocytes are produced in response to an infection. True or false?

Answer 9

False. Specific lymphocytes are not produced in response to an infection but they already exist.

Question 10

How do non specific responses occur?

Answer 10

Response is immediate + same goes for all pathogens

Question 11

Give examples of non specific responses

Answer 11

• Phagocytosis by phagocytes

* Physical barrier e.g skin

Question 12

How many lymphocytes are there approx. present at any time?

Answer 12

10 million

Question 13

What are lymphocytes constantly doing in the fetus?

Answer 13

The lymphocytes are constantly colliding with other cells - will collide almost exclusively with body’s own material

Question 14

Why is infection in the fetus rare?

Answer 14

As it is protected from the outside world by the mother (in particular the placenta)

Question 15

What two things can happen to lymphocytes that fit exactly with the body’s own cells?

Answer 15

They will either die or be suppressed

Question 16

What do the remaining lymphocytes do (the lymphocytes that don’t fit with the body’s own cells)?

Answer 16

The only remaining lymphocytes are those that might fit foreign material + therefore only respond to foreign material

Question 17

Where are lymphocytes in adults found?

Answer 17

Lymphocytes in adults are found in the bone marrow (initially only encounter self-antigens)

Question 18

What happens to any lymphocytes that show an immune response to self-antigens?

Answer 18

These lymphocytes undergo programmed cell death (apoptosis) before they can differentiate into mature lymphocytes

Question 19

Will clones of anti-self lymphocytes appear in the blood?

Answer 19

No - this leaves only those that might respond to non-self antigens

Question 20

Name barriers to infection + why they are useful

Answer 20

• Skin - pathogens find it difficult to penetrate
• Hydrochloric acid - denatures the enzymes or proteins of most pathogens that enter the stomach
• Epithelial mucus - epithelial layers inside the body produce mucus that pathogens stick to + become immobilised