Secondary non-specific defences 4.1.5

Question 1

What are secondary defences?

Answer 1

Used to combat pathogens that have entered the body.

Question 2

What are antigens

Answer 2

They are chemical markers presented on the outer membrane, which are recognised as foreign

Question 3

What are opsonins

Answer 3

They are chemicals that bind to pathogens and ‘tag’ them so they can be more easily recognised by phagocytes.

Question 4

What are phagocytes?

Answer 4

They are specialised cells in the blood and tissue fluid which engulf and digest pathogens

Question 5

What is the most common phagocyte?

Answer 5

Neutrophils

Question 6

Where are neutrophils made?

Answer 6

The bone marrow

Question 7

What do neutrophils contain?

Answer 7

• Many lysosomes (with many digestive enzymes)
• Lobed nucleus

Question 8

Where do dead neutrophils collect?

Answer 8

They collect in an area of infection, to form pus

Question 9

Describe neutrophils digest and engulf pathogens

Answer 9

• Neutrophil binds to the opsonin attached to the antigen of the pathogen
• The pathogen is engulfed by endocytosis forming a phagosome
• Lysosomes fuse to the phagosome and release lytic enzymes into it
• After digestion the harmless products can be absorbed into the cell

Question 10

What are macrophages?

Answer 10

• Round nucleus!

They are larger cells manufactured in the bone marrow, and play a role in initiating the specific responses to invading pathogens.
When the pathogen is destroyed in the macrophage, its antigens combine with glycoproteins in the cytoplasm, this takes the antigen to the cell surface membrane and is now an antigen presenting cell.
This stimulates the specific response

Question 11

What happens to the antigen presenting cell when it becomes initiated?

Answer 11

The APC moves around the body where it can come into contact with specific cells that can activate the full immune response (which are T lymphocytes and B lymphocytes)

Question 12

How do cells increase the chances that lymphocytes will recognise the antigens?

Answer 12

As there is only one B cell and T cell with the correct recognition site for each antigen - and therefore by presenting antigens on their cell membrane the chance of an antigen being recognised is increased.

Question 13

What is clonal selection?

Answer 13

The activation of T cells and B cells - which will eventually lead to a complex series of events that causes the production of an antibody that can combat the specific pathogen, and also create memory cells that will provide long term immunity.

Question 14

What is clonal selection (and the events following this) coordinated by?

Answer 14

The hormone-like chemicals cytokines, which stimulate the differentiation and activity of macrophages, T cells and B cells.

Question 15

Briefly describe what interferons are

Answer 15

They are a group of chemicals that are produced then cells are invaded by viruses

Question 16

What do interferons do?

Answer 16

• Diffuses from the cell where it is made into the surrounding cells
• Then binds to receptors in the surface membrane of uninfected cells
• This stimulates a pathway which makes the cells resistant to infection by viruses by stopping them reproducing
• This prevents the infection of more cells when the virus breaks out of the first cell

Question 17

What do phagocytes look like when they accumulate?

Answer 17

Pus

Question 18

Where do phagocytes originate from?

Answer 18

Bone marrow/foetal liver

Question 19

What is involved in phagocytosis?

Answer 19

2 groups of white blood cells, the neutrophils and macrophages, which are both known as phagocytes as they both ingest pathogens

Question 20

What is phagocytosis seen in association with?

Answer 20

Inflammation