4.1.1 The immune system

Question 1

What are the two main types of defence mechanisms in the body?

Answer 1

Non-specific defences and specific defences.

Question 2

What are non-specific defences?

Answer 2

Fast-acting mechanisms that respond the same way to all pathogens.

Question 3

What are specific defences?

Answer 3

Slower mechanisms that produce a targeted response to each pathogen.
They also provide long-term immunity.

Question 4

List 5 primary non-specific defence mechanism.

Answer 4

Skin
Mucuous membranes
Expulsive forces
Blood clotting & wound repair
Inflammation

Question 5

How does the skin act as a physical and chemical barrier?

Answer 5

Physical - physical barrier to block pathogens fron entering
Chemical - produces sebum, an anitimicrobial substance that lower pH to inhibit growth of pathogens.

Question 6

Where are mucous membranes found and what do they do?

Answer 6

They line the ears, nose, throat, and digestive tract
They trap pathogens using mucus and destroy them with lysozymes.

Question 7

What are expulsive reflexes and how do they defend the body?

Answer 7

Coughing or sneezing
Expel pathogens from the gas exchange system

Question 8

How does blood clotting help prevent infection?

Answer 8

It seals wounds quickly to block pathogen entry.

Question 9

What happens after a blood clot forms?

Answer 9

It dries into a scab, under which epidermal cells divide, blood vessels regrow, and collagen strengthens the new tissue.
The scab then breaks off and the wound is healed.

Question 10

How does inflammation prevent pathogen spread?

Answer 10

Blood vessel dilate (widen) increasing blood flow to that area, making it hotter.
Bloos vessels also become more permeable so they start to leak tissue fluid, causing swelling and isolating any pathogens.

Question 11

What is an antigen?

Answer 11

Unique molecule (usually proteins) that can be found on the surface of cells.

Question 12

How does the immune system use antigens?

Answer 12

To distinguish self from non-self and target foreign cells for destruction.

Question 13

What 4 things can antigens help the immune system identify?

Answer 13

• Pathogens
• Abnormal body cells
• Toxins
• Cells from other organsism of the same species

Question 14

What are phagocytes, generally?

Answer 14

White blood cells that engulf and destroy pathogens as part of the non-specific immune response.
Can also act as Anigen presenting cells (APC)

Question 15

Where are phagocytes found and produced?

Answer 15

Found in the blood and tissues of many organisms.
Produced in bone marrow

Question 16

What are the two main types of phagocytes?

Answer 16

Neutrophils and Macrophages

Question 17

What about the structure of neutrophils and macropahages make them identifiable in blood smears?

Answer 17

Neutrophils - Multi-lobed nucleus, smaller and have granules in cytoplasm
Macrophages - kidney shaped/crescent moon nucleus and larger

Question 18

What is the role of neutrophils?

Answer 18

Rapidly engulf and destroy pathogens at the site of infections.

Question 19

What is the role of macrophages?

Answer 19

Engulf and digest pathogens
Also present the pathogen’s antigens on its cell surface to activate other cells in the immune system.

Question 20

Describe the process of phagocytosis.
(7 steps)

Answer 20

1. The pathogen releases chemicals that attract a phagocyte.
2. The phagocyte recognises the pathogen’s antigens as non-self, so phagocyte binds to the pathogen
3. The phagocyte then engulfs the pathogen
4. The pathogen is now contain wihtin a vesicle, known as a ‘phagosome’.
5. A lysosome, with hydrolytic enzymes called lysozymes, fuses with the phagosome to form a phagolysosome.
6. Lysozymes digest and destroys the pathogen.
7. The phagocyte presents the pathogen’s antigens on its surface to activate other cells in immune system -
   the phagocyte is reffered to as an APC.

Question 21

What are cytokines?

Answer 21

Cell-signalling chemicals released by phagocytes after engulfing a pathogen.

Question 22

What do cytokines do? (2 roles)

Answer 22

1. Attract other phagocytes to the site of infection.
2. Increase body temperature to inhibit pathogens and speed up the specific immune response.

Question 23

What are opsonins?

Answer 23

Chemicals (e.g. antibodies) that bind to pathogens to make them easier to recognise and engulf by phagocytes.

Question 24

What type of white blood cells are involved in specific immunity?

Answer 24

Lymphocytes - T and B cells

Question 25

Where do **T lymphocytes** mature and what do they respond to?

Answer 25

Mature in the **thymus gland**. Involved in **cellular response** - they respond to antigens presented on body cells.

Question 26

Where do **B lymphocytes** mature and what is their role?

Answer 26

Mature in **bone marrow**. Involved in **humoral response** - produce antibodies found in body fluid (or humors).

Question 27

What are the 4 types of T cell?

Answer 27

1. T helper cells 2. T killer cells 3. T regulatory cells 4. T memory cells

Question 28

What do **T helper** cells do?

Answer 28

* Have receptors on their cell surface that bind to **complementary antigens** on APC. * They produce **interleukins** - which stimulate B cells or phagocytes * Can also form T memory or T killer cells.

Question 29

What do **T killer** cells do?

Answer 29

Kill abnormal or foreign cells by producing **perforin** - Makes **holes** in cell surface membrane = freely permeable and causes cell death.

Question 30

What is the function of **T regulator** cells?

Answer 30

**Suppress** the immune system after infection to prevent **autoimmune** responses.

Question 31

What do T memory cells do?

Answer 31

Provide **long-term immunity** against specific pathogens. Rapid repsonse if body is re-infected with same pathogen.

Question 32

What are the stages of the cellular response or T lymphocyte response?

Answer 32

1. **Clonal selection** - T cells, with complementary receptors to the antigens on the APC, bind to the antigens - this activates the T cell. 2. **Clonal expansion** - Once it is activated, the T cell divides by mitosis to produce genetically identical clones

Question 33

What can cloned T cells become or do?

Answer 33

* Develop into memory cells - provide long-term immunity * Develop into T killer cells - destroy infected cells * Release interleukins to stimulate phagocytosis * Release interleukins to stimulate B lymphocytes and produce antibodies.

Question 34

What is the humoral response?

Answer 34

A **specific** defence mechanism involving B cells that produce **antibodies** found in body fluids (humors) to destroy pathogens.

Question 35

Name the key cells involved in the humoral response.

Answer 35

* B cells * Plasma cells * Memory cells * T helper cells

Question 36

What is the role of plasma cells?

Answer 36

Type of B cell that can produce and secrete antibodies against a specfic antigen They have a short life span

Question 37

What is the role of memory cells?

Answer 37

Type of B cell that provide long-term immunity against specific pathogens. Longer life span than plasma cells Can rapidly divide into plasma cells

Question 38

What are the stages of the humoral response?

Answer 38

1. B cell ,with complementary antibody, binds to antigen 2. B cell engulfs pathogen and presents its antigen 3. T helper cell activates B cell (**clonal selection**) 4. B cell divides (**clonal expansion**) 5. Plasma cells produce antibodies 6. Memory cells provide long-term immunity

Question 39

Describe the **primary** immune response.

Answer 39

* **First exposure** to pathogen * **Slower antibody production** (longer lag phase) - very few B cells that are specific to pathogen's antigens * Time between pathogen exposure & antibody production = **4-7 days**. * Symptoms are usually **experienced** - it takes time for B cells to divide into plasma cells to produce correct antibody. * **Memory cells** are formed

Question 40

Describe the **secondary** immune response.

Answer 40

* **Faster, stronger** response due to **memory cells** * **Rapid antibody production** (shorter lag phase) - memory cells **recognise** pathogen's antigens & quickly divide into plasma cells. * Time between pathogen exposure & antibody production = **1-3 days**. * Pathogen destroyed **before symptoms** occur

Question 41

What is an **autoimmune disease**?

Answer 41

An autoimmune disease occurs when the immune system **attacks the body’s own cells**, failing to recognise 'self' antigens. Causes breakdown of healthy tissues

Question 42

Name three autoimmune diseases and what they affect.

Answer 42

1. Type 1 diabtes - immune system attacks **insulin-secreting** cells of the pancreas (beta cells) = lack of insulin 2. Lupus - immune system attacks cells in **connective tisssue** = inflammation 3. **Arthritis** - immune system attacks cells in the **joints** = pain and inflammation.

Question 43

What is the overall structure of an antibody?

Answer 43

Y-shaped glycoproteins Four polypeptide chains: 2 heavy chains & 2 light chains Polypeptide chains connected via disulfide bridges Constant region, Variable region and hinge region.

Question 44

Draw out the stucture of an antibody.

Answer 44

4 chains constant, variable and hinge regions labelled disulfide bridges labelled heavy chain and light chain labelled

Question 45

What does the constant region of an antibody do?

Answer 45

It is the same for all antibodies Binds to receptors on immune cells such as B cells.

Question 46

What is the function of the variable region in an antibody?

Answer 46

Different for each antibody - its shape is complementary to a specific antigen. This part binds with the antigen.

Question 47

Why is the hinge region of an antibody important?

Answer 47

Gives flexibilty so the antibody can bind to multiple antigens at once.

Question 48

What is formed when an antibody binds to an antigen?

Answer 48

An antigen-antibody complex.

Question 49

What are the three ways in which antibodies work to destroy pathogens?

Answer 49

* **Agglutination** - involves clumping pathogens together for easier phagocytosis * **Neutralising toxins** - antibodies bind to toxins to inactivate them. * **Opsonisation** - binding to pathogens, marking them for destruction by phagocytes. * Prevent pathogens from binding to host cells by **blocking** the pathogen's cell surface membrane.