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Biology A-Level > The immune response, antibodies and WBC count (Chapter 11) > Flashcards

The immune response, antibodies and WBC count (Chapter 11) Flashcards

1
Q

Define immunity

A

The protection against disease provided by the body’s internal defence/immune system

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2
Q

What 3 things constitute the external defence system?

A

Skin, HCl in stomach, blood clotting

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3
Q

What is an antigen?

A

A substance foreign to the body which stimulates an immune response

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4
Q

Which cells recognise antigens?

A

WBCs

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5
Q

What are examples of antigens?

A

Glycoproteins on the surface of pathogens or their waste material

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6
Q

What is an antibody?

A

A glycoprotein (immunoglobulin) made by plasma cells derived from B-lymphocytes, secreted in response to an antigen

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7
Q

What is the immune response?

A

The complex series of responses of the body to the entry of a foreign antigen, involving the activity of lymphocytes and phagocytes

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8
Q

Define self substances

A

Substances produced by the body that the immune system does not recognise as foreign ∴ they do not stimulate an immune response

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9
Q

Define non-self substances

A

Any substance/cell that is recognised by the immune system as being foreign and will stimulate an immune response

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10
Q

Where do the cells of the immune system originate from?

A

The bone marrow

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11
Q

What are the two groups of WBCs?

A

Phagocytes and lymphocytes

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12
Q

What are the two groups of phagocytes?

A

Neutrophils and macrophages

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13
Q

Describe the characteristics of phagocytes

A
  • They are produced throughout life in the bone marrow and are stored there before being distributed around the body in the blood
  • They remove any dead cells and invasive microorganisms
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14
Q

Describe the characteristics of neutrophils

A
  • Smaller than macrophages

- Short-lived cells

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15
Q

Describe the characteristics of macrophages

A
  • Larger than neutrophils
  • Found in organs rather than blood e.g. liver/kidney
  • After they are made in the bone marrow, they travel in the blood as monocytes, which develop into macrophages in the organs
  • They are long-lived cells
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16
Q

What is the role of macrophages in the immune response?

A

They do not destroy pathogens completely but cut them up to display antigens that be recognised by lymphocytes

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17
Q

Describe the role of neutrophils in the immune response (5 stages)

A

1) Neutrophils move towards the pathogens, attracted by chemicals released e.g. histamine by the cells under attack and the pathogens, which may be clustered together and covered in antibodies
2) The ABs further stimulate the neutrophils to attack the pathogens bc the neutrophils have receptor proteins on their surfaces that recognise AB molecules and attach to them
3) When the neutrophil attaches to the pathogen, the neutrophil’s CSM engulfs the pathogen and traps it within a phagocytic vacuole (endocytosis/phagocytosis)
4) Lysosomes and the phagocytic vacuole fuse
5) Digestive enzymes are secreted into the phagocytic vacuole ∴ destroying the pathogen

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18
Q

What happens after the neutrophils kill and digest some pathogens?

A

The neutrophils die and often collect at the site of infection to form pus

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19
Q

Describe the characteristics of lymphocytes

A
  • Smaller than phagocytes

- They have a large nucleus that fills most of the cell

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20
Q

What are the two types of lymphocytes?

A

B and T cells

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21
Q

Where and when are lymphocytes produced

A

In the bone marrow before birth

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22
Q

What type of lymphocytes can carry out immune responses?

A

Mature lymphocytes

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23
Q

How are B and T cells specialised and what does this mean?

A

Each type of mature B and T cell is specialised to respond to one antigen ∴ they can overall respond to any type of antigen

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24
Q

What happens as B cells mature?

A
  • B cells remain in the bone marrow until they are mature and then spread throughout the body, concentrating in lymph nodes and the spleen
  • As each B cell matures, il gains the ability to make just one type of AB molecule - the genes that code for ABs are changed in a variety of ways to code for diff ABs
  • Each cell then divides to give a small no. of clones that can all make the same type of AB
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25
Q

What happens to ABs before an immune response?

A

They remain in the CSM - part of each AB forms a glycoprotein receptor, which can combine specifically with one type of antigen

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26
Q

Describe the response of a B cell to an antigen

A

1) Clonal selection - when the antigen enters the body for the first time, the B cells with receptors complementary to the antigen are stimulated to divide by mitosis
2) Clonal expansion - the small clone of cells divide repeatedly by mitosis so that a huge number of identical B cells are produced over a few weeks
3) Some of the activated B cells become plasma cells that produce AB molecules v quickly and secrete them into diff parts of the body e.g. blood and lymph
4) Other B cells become memory cells which remain circulating in the body for a long time

27
Q

How long do plasma cells live?

A

Not very long (several weeks) but the AB molecules that they have secreted stay in the blood for longer, but eventually decrease in concentration too

28
Q

Why is the primary response to the antigen slow?

A
  • At this start of the response, there are v few B cells that are specific to the antigen and it take time for them to be selected and cloned
  • It also takes time for the T helper cells to become activated
29
Q

Why is the secondary response to the antigen much faster?

A
  • There are now many memory cells which divide rapidly and differentiate/develop into plasma cells and more memory cells
  • ∴ many more ABs are produced and the pathogens can be destroyed and removed before any symptoms develop
  • clonal selection and expansion happens much faster
30
Q

How come some viral infections can infect repeatedly when we have memory cells?

A

There are many different and new strains of the viruses e.g. cold and flu each with different antigens ∴ there is only and always a primary response, during which time we often become ill

31
Q

What do memory cells form the basis of?

A

Immunological memory

32
Q

What do memory cells prevent us from doing?

A

Suffering from the certain diseases twice

33
Q

Where are T cells produced

A

In the bone marrow

34
Q

Where do T cells mature?

A

In the thymus

35
Q

What is the thymus?

A

A gland that lies in the chest just beneath the sternum

36
Q

What do mature T cells have?

A

T cell receptors - cell surface receptors which are each specific to one antigen and have a similar structure to that of ABs

37
Q

When/how are T cells activated?

A

When they encounter the antigen on another cell of the host e.g. a macrophage that has engulfed the pathogen and is exposing the pathogen’s surface molecules OR a body cell invaded by a pathogen, displaying the antigen on its CSM as a ‘help’ signal

38
Q

What is antigen presentation?

A

The display of the pathogen’s antigens on a body cell or phagocyte that is affected by the pathogen

39
Q

What happens when T cells are activated?

A

Clonal selection and clonal expansion take place - those T cells with receptors complementary to the antigen respond by dividing by mitosis to increase to no. of cells

40
Q

What are the two main types of T cell?

A

1) helper T cells

2) killer (cytotoxic) T cells

41
Q

What happens when helper T cells are activated?

A

1) They release hormone-like cytokines that stimulate appropriate B cells to divide and develop into plasma cells (and memory cells) which secrete ABs
2) Some secrete cytokines that stimulate macrophages to carry out phagocytosis more vigorously
3) Some stimulate killer T cells to divide by mitosis and to differentiate by producing vacuoles full of toxins

42
Q

What is the role of killer T cells?

A

1) They search the body for cells that have become invaded by pathogens and are displaying foreign antigens from the pathogens on their CSM
2) They recognise the antigens, attach themselves to the surface of infected cells and secrete toxic substances e.g. hydrogen peroxide into the infected cell through the CSM, killing the body cells and pathogens inside

43
Q

What also happens during a T cell response?

A

Memory helper and killer T cells are produced, which remain in the body and become active v quickly during the secondary response to the antigen

44
Q

Summarise the structure of antibodies

A
  • Globular proteins with a quaternary structure

- They form the group of plasma proteins called immunoglobulins

45
Q

Describe in detail the structure of antibodies

A
  • Consists of 4 polypeptide chains: 2 long/heavy chains and 2 short/light chains
  • Disulfide bonds hold the chains together
  • Each molecule has 2 identical antigen-binding sites, which are formed by both the light and heavy chains
  • The antigen-binding sites form the variable region, which is different on each type of AB molecule
  • The region which is universal to all AB molecules is the constant region
  • The hinge region gives the flexibility for the AB molecule to bind around the antigen
46
Q

What is the antibody-antigen complex similar to?

A

The enzyme-substrate complex

47
Q

What are 6 ways that ABs work to protect the body?

A

1) ABs combine with viruses and bacterial toxins, preventing them from entering or damaging cells
2) ABs attach to flagella of bacteria, making them less active and easier for phagocytes to engulf
3) ABs with multiple antigen-binding sites cause agglutination of bacteria, reducing the chances of spread throughout the body
4) Some ABs ‘punch’ holes in the cell walls of bacteria, causing them to burst (lysis) when they absorb water by osmosis
5) ABs coat bacteria, making it easier for phagocytes to ingest them
6) ABs (antitoxins) combine with toxins, neutralising them and making them harmless

48
Q

How are phagocytes able to use ABs as labels to identify antigens and destroy them?

A

Phagocytes have receptors proteins for the heavy polypeptide chains of ABs

49
Q

What are the 4 key characteristics of the immune system?

A

1) It can distinguish self from non-self
2) It can be specific
3) It is diverse - can recognise millions of different antigens
4) It has immunological memory

50
Q

Why might plasma cells have extensive ER and ribosomes?

A

To make and secrete many proteins as antibodies

51
Q

What do the results of blood tests normally include?

A

The no. of RBCs, WBCs and platelets

52
Q

What are platelets?

A

Small cell fragments which release substances that stimulate blood clotting

53
Q

How are the results for specific WBCs e.g. neutrophils/lymphocytes given?

A

As absolute numbers or as a % of WBC count

54
Q

When does the number of neutrophils in the blood increase?

A

During bacterial infections and whenever tissues become inflamed and die

55
Q

When does the number of lymphocytes in the blood increase?

A

During viral infections and TB

56
Q

When does the number of (helper) T cells decrease and why?

A

HIV invades helper T cells and causes their destruction, ∴ if the number of T cells is low, the disease has progressed more and treatment is less successful

57
Q

What do all WBCs in the blood originate from?

A

Stem cells in the bone marrow

58
Q

What are the two groups of bone marrow stem cells and what do each of them give rise to?

A

1) myeloid stem cells give rise to phagocytes

2) lymphoid stem cells give rise to lymphocytes

59
Q

What are leukaemias?

A

Cancers of the stem cells

60
Q

What happens in a person with leukaemia?

A
  • The cells divide uncontrollably to give many cells which do not differentiate properly (are immature) and disrupt the production of normal blood cells incl RBCs and platelets, ∴ the body does not have enough of these
  • These malignant cells fill up the body, disrupting the normal balance of components in the blood
  • This causes anaemia and increases the risk of excessive bleeding
  • Also, the no. of mature neutrophils and lymphocytes decrease, ∴ the people affected become immunosuppressed (more susceptible to infections)
61
Q

What are the two types of leukaemia?

A

Acute and chronic

62
Q

What happens in acute leukaemias?

A
  • Develop very quickly
  • Have severe effects
  • Need to be treated immediately after they are diagnosed
63
Q

What happens in chronic leukaemias?

A
  • May take years to develop
  • Changes in blood cell count are usually monitored over time so that treatment is given when it is most likely to cure the disease
64
Q

How are blood tests used with leukaemias?

A

1) To help diagnose them
2) Monitor their progress
3) Assess the effectiveness of treatments

Biology A-Level (44 decks)

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