Immunity 4.8

Question 1

What is the purpose of the first lines of defence?

Answer 1

The physical barriers that are designed to keep harmful micro-organisms from entering the body.

Question 2

How is the skin a first line of defence?

Answer 2

Usually prevents invading microorganisms unless it is physically disrupted.

Question 3

How are mucus and cilia the first line of defence?

Answer 3

The respiratory tract has upper airway filters. Invading organisms get trapped in the mucus and the cilia on the epithelial cells transports them away from the lung.

Question 4

How are mucous membranes the first line of defence?

Answer 4

Many mucous membranes are bathed in secretions that have antimicrobial properties.

Question 5

How are digestive system barriers the first line of defence?

Answer 5

They include the acid pH of the stomach and the antibacterial activity of the pancreatic enzymes, bile, and intestinal secretions. Peristalsis and the normal loss of epithelial cells remove microorganisms. If peristalsis is slowed, e.g. due to drugs, removal is delayed and prolongs some infections. Normal bowel flora can inhibit pathogens; alteration of this flora with antibiotics can allow pathogenic microorganisms to grow.

Question 6

How are reproductive system barriers the first line of defence?

Answer 6

It includes the length of the urethra in men, the acid pH of the vagina in women, and the concentrated solution of the urine being formed in the kidney. The kidney also produces and excretes large amounts of mucus which binds to certain bacteria making it easier to get rid of them from the body.

Question 7

How is vitamin C a first line of defence?

Answer 7

A deficiency of vitamin C can lead to weakened connective tissue - this makes it easier for microbes to enter the body and wounds take a lot longer to heal and therefore more open to infection.

Question 8

What is phagocytosis?

Answer 8

Phagocytes or macrophages are self-motile and move around the body through the connective tissue, the blood vessels and over the surfaces of body cavities. They can change shape and engulf foreign bodies, such as bacteria that may have entered the body. The phagocytes are attracted to the sites of infection but this is a non-specific localised response.

Question 9

What is inflammation?

Answer 9

Localised defense mechanism. The four main symptoms are; pain, redness, heat and swelling.

Question 10

What is the purpose of inflammation?

Answer 10

1: Destroy the cause of infection
2: Limit the effects on the body by confining the infection to a small area
3: Replace or repair damaged tissue.

Question 11

What are the steps of the inflammatory response?

Answer 11

1: Increased diameter and permeability of blood vessels in the infected area resulting in increased blood flow to the tissues. This allows defence cells to reach the tissues faster. Blood clots also form if blood vessels have been damaged.
2: Phagocytes are attracted to the invading microbes and start to engulf them. After a few days an abscess forms - this is full of pus - consisting of dead phagocytes, damaged tissue and various body fluids.
3: New cells are formed to replace damaged tissue.

Question 12

What is the immune system responsible for?

Answer 12

It enables us to:
- Recognise our own tissues
- recognise foreign antigens
- produce an immune response to destroy foreign material that enters the body.
Immunity is the ability to resist disease.

Question 13

What does the immune response rely on?

Answer 13

The fact that all of our cells carry markers called antigens on the cell membranes.

Question 14

What are antibodies made of?

Answer 14

They are large proteins that have a globular form and are made from four polypeptide chains. Each molecule has two binding sites that are able to bind to a specific antigen.

Question 15

What happens when antibodies bind to antigens?

Answer 15

They can:
- neutralise the antigen
- inhibit the antigen
- destroy the antigen

Question 16

How do antibodies slow down microorganisms?

Answer 16

If antigens are bound to a microorganism the antibodies can cross-link the microorganisms. This slows them down and makes it easier for macrophages to engulf them and destroy them.

Question 17

What are anti-toxins?

Answer 17

They are a specific type of antibody that bind to toxins produced by bacteria. This neutralises the effect of the toxin and makes the toxin harmless.

Question 18

What does the immune system rely on?

Answer 18

A number of different types of white blood cell. These are formed in the bone marrow.

Question 19

What are lymphocytes?

Answer 19

White blood cells that are small, round and have a round nucleus. Formed from a human stem cell.

Question 20

What are macrophages?

Answer 20

White blood cells that are large, mostly with a multi-lobed nucleus. Formed from a human stem cell.

Question 21

Where do the white blood cells accumulate?

Answer 21

Once passed into the circulation, many accumulate in the lymph glands and the spleen - in these organs body fluids can be filtered and invading microorganisms killed.

Question 22

What are B lymphocytes?

Answer 22

The cells that produce antibodies that can bind to and destroy antigens - this is called the humoral response

Question 23

Where are B lymphocytes matured?

Answer 23

They are matured and activated in the bone marrow.

Question 24

How do B lymphocytes grow?

Answer 24

In B lymphocytes the antibody is bound to the cell membrane - once they have been activated by T helper lymphocytes they multiply in number and then grow and differentiate to form plasma cells that can secrete antibody.

Question 25

What are T lymphocytes?

Answer 25

They are responsible for a type of immune response in which cells kill and destroy invading microbes directly - this is called cell-mediated immune response.

Question 26

Where are T lymphocytes matured?

Answer 26

They are matured and activated in the thymus gland - this gland is only present in mammals until the offspring have stopped being breast-fed i.e. they have been weaned.

Question 27

What are T helper lymphocytes?

Answer 27

They recognise foreign antigens on the surface of macrophages.

Question 28

What are T killer lymphocytes?

Answer 28

The cells that actively destroy other cells.

Question 29

What are T suppressor lymphocytes?

Answer 29

They turn off the immune response once a pathogen had been destroyed.

Question 30

What are T memory lymphocytes?

Answer 30

They remain in the circulation and are activated if they recognise the foreign antigen at another time.