2.4 Defence mechanisms

Question 1

What is an infection?

Answer 1

• An interaction between the pathogen and the body’s various defence mechanisms.
• Sometimes the pathogen overwhelms the defences and the individual dies
• Sometimes the body’s defence mechanisms overwhelm the pathogen and the individual recovers from the disease

Question 2

What is immunity?

Answer 2

Having overwhelmed the pathogen, the body’s defences seem to be better prepared for a second infection from the same pathogen and can kill it before it can cause any harm

Question 3

What is the immune system?

Answer 3

A system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells

Question 4

How can pathogens enter the body?

Answer 4

• The eye
• The respiratory system
• The skin
• The stomach
• The urinary tract and vagina
• Saliva

Question 5

How can pathogens enter the body through the eye?

Answer 5

• Tears and the conjunctiva and antibacterial enzymes

Question 6

How can pathogens enter the body through the respiratory system?

Answer 6

Muscles and cilia

Question 7

How can pathogens enter the body through the skin?

Answer 7

Sebum and sweat

Question 8

How can pathogens enter the body through the stomach?

Answer 8

Hydrochloric acid

Question 9

How can pathogens enter the body through the saliva?

Answer 9

Antibacterial enzymes

Question 10

What are pathogens?

Answer 10

Microorganisms that cause disease

Question 11

What impact do parasites have?

Answer 11

They have a close relationship with their host, and have a negative impact on the host

Question 12

What conditions are needed in the stomach to kill pathogens?

Answer 12

Acidic conditions in the stomach kill pathogens

Question 13

What is toxic to pathogens?

Answer 13

Antibacterial enzymes in tears and saliva are toxic to pathogens

Question 14

What is the urinary tract protected by?

Answer 14

The urinary tract is protected by the urine which flushes out microorganisms

Question 15

What does the vaginal tract contain?

Answer 15

The vaginal tract contains acid

Question 16

What is the respiratory system protected by?

Answer 16

The respiratory system is protected by goblet cells and mucus

Question 17

What are the two types of defence mechanisms?

Answer 17

• Non specific
• Specific

Question 18

How do you defend the body from invasion by foreign material?

Answer 18

To defend the body from invasion by foreign material, lymphocytes must be able to distinguish the body’s own cells and molecules (self) from those that are foreign (non-self).

Question 19

What happens if the body could not defend itself from invasion by foreign material?

Answer 19

If they could not do this, the lymphocytes would destroy the organisms own tissues

Question 20

What do each type of cells have on its surface?

Answer 20

Each type of cell, self or non-self, has specific molecules on its surface that identify it

Question 21

Why are proteins the most important of the specific molecules that identify it?

Answer 21

Because proteins have enormous variety and a high specific tertiary structure. It is this variety of specific 3D structure that distinguishes one cell from another

Question 22

What do the protein molecules allow the immune system to identify?

Answer 22

• Pathogens, for example the human immunodeficiency virus
• Non-self material such as cells from other organisms of the same species
• Toxins including those produced by certain pathogens like the bacterium that causes cholera
• Abnormal body cells such as cancer cells

Question 23

What are the implications for humans of protein molecules allowing the immune system to identify things?

Answer 23

• It has implications for humans who have had tissue or organ transplants
• The immune system recognises these as non-self even though they have come from individuals of the same species
• Therefore attempts to destroy the transplant

Question 24

How can you minimise the effect of tissue rejection?

Answer 24

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

Question 25

What are the types of non-specific defence mechanisms?

Answer 25

• Physical barrier e.g skin
• Phagocytosis

Question 26

What is a non specific defence mechanism?

Answer 26

The response is immediate and the same for all pathogens

Question 27

What is a specific defence mechanim?

Answer 27

The response is slower and specific to each pathogen

Question 28

What are the types of specific defence mechanisms?

Answer 28

• cell-mediated response e.g T lymphocytes
• Humoral Response e.g B lymphocytes

Question 29

How do lymphocytes recognise cells belonging to the body?

Answer 29

• There are around 10 million different lymphocytes present at any time, each capable of recognising a different chemical shape
• In the foetus, these lymphocytes are constantly colliding with other cells
• Infection in the foetus is rare because it is protected from the outside world by the mother and, in particular, the placenta
• Lymphocytes will therefore collide almost exclusively with the body’s own material (self)
• Some of the lymphocytes will have receptors that exactly fit those of the body’s own cells
• These lymphocytes either die or are suppressed
• The only remaining lymphocytes are those that might fit foreign material, and therefore only respond to foreign material
• In adults, lymphocytes produced in the bone marrow initially only encounter self-antigens
• Any lymphocytes that show an immune response to these self-antigens undergo programmed cell death before they can differentiate into mature lymphocytes
• No clones of these anti self lymphocytes will appear in the blood, leaving only those that might respond to non-self antigens

Question 30

What 2 forms do lymphocytes take?

Answer 30

• Cell mediated responses involving T lymphocytes
• Humoral responses involving B lymphocytes