Chapter 11.1

Question 1

what are Phagocytes

Answer 1

are white blood cells that are produced continuously in the bone marrow

Question 2

where are phagocytes stored

Answer 2

in the bone marrow before being distributed around the body in the blood

Question 3

function of phagocytes

Answer 3

• They are responsible for removing dead cells and invasive microorganisms
• They carry out what is known as a non-specific immune response

Question 4

There are two main types of phagocyte

Answer 4

• Neutrophils
• Macrophages
• As both are phagocytes, both carry out phagocytosis (the process of recognising and engulfing a pathogen) but the process is slightly different for each type of phagocyte

Question 5

Neutrophils

Answer 5

• Neutrophils travel throughout the body and often leave the blood by squeezing through capillary walls to ‘patrol’ the body tissues
• During an infection, they are released in large numbers from their stores
• However, they are short-lived cells

Question 6

The stages of phagocytosis, as carried out by a neutrophil

Answer 6

Question 7

Neutrophils mode of action

Answer 7

• Chemicals released by pathogens, as well as chemicals released by the body cells under attack (eg. histamine), attract neutrophils to the site where the pathogens are located (this response to chemical stimuli is known as chemotaxis)
• Neutrophils move towards pathogens (which may be covered in antibodies)
• The antibodies are another trigger to stimulate neutrophils to attack the pathogens (neutrophils have receptor proteins on their surfaces that recognise antibody molecules and attach to them)
• Once attached to a pathogen, the cell surface membrane of a neutrophil extends out and around the pathogen, engulfing it and trapping the pathogen within a phagocytic vacuole
• This part of the process is known as endocytosis
• The neutrophil then secretes digestive enzymes into the vacuole (the enzymes are released from lysosomes which fuse with the phagocytic vacuole)
• These digestive enzymes destroy the pathogen
• After killing and digesting the pathogens, the neutrophils die
• Pus is a sign of dead neutrophils

Question 8

Macrophages

Answer 8

• Macrophages are larger than neutrophils and are long-lived cells
• Rather than remaining in the blood, they move into organs including the lungs, liver, spleen, kidney and lymph nodes
• After being produced in the bone marrow, macrophages travel in the blood as monocytes, which then develop into macrophages once they leave the blood to settle in the various organs listed above

Question 9

Mode of action: Macrophages

Answer 9

• Macrophages play a very important role in initiating an immune response
• Although they still carry out phagocytosis in a similar way to neutrophils, they do not destroy pathogens completely
• They cut the pathogens up so that they can display the antigens of the pathogens on their surface (through a structure called the major histocompatibility complex)
• These displayed antigens (the cell is now called an antigen-presenting cell) can then be recognised by lymphocytes (another type of white blood cell)

Question 10

Lymphocytes

Answer 10

are another type of white blood cell

• They play an important part in the specific immune response
• They are smaller than phagocytes
• They have a large nucleus that fills most of the cell
• They are produced in the bone marrow before birth

Question 11

There are two types of lymphocytes (with different modes of action). The two types of lymphocytes are:

Answer 11

-B-lymphocytes (B cells)

T–lymphocytes (T cells)

Question 12

B-lymphocytes (B cells)

Answer 12

remain in the bone marrow until they are mature and then spread through the body, concentrating in lymph nodes and the spleen

• Millions of types of B-lymphocyte cells are produced within us because as they mature the genes coding for antibodies are changed to code for different antibodies
• Once mature, each type of B-lymphocyte cell can make one type of antibody molecule
• At this stage, the antibody molecules do not leave the B-lymphocyte cell but remain in the cell surface membrane
• Part of each antibody molecule forms a glycoprotein receptor that can combine specifically with one type of antigen

Question 13

If that antigen enters the body

Answer 13

-B-lymphocyte cells with the correct cell surface receptors will be able to recognise it and then divide by mitosis (clonal selection)

Question 14

-During a primary immune response, B-lymphocytes

Answer 14

divide repeatedly by mitosis (clonal expansion) and differentiate into two main types of cell:

• Plasma cells
• Memory cells

Question 15

The maturation of B-lymphocytes

Answer 15

Question 16

T-lymphocytes

Answer 16

• Immature T-lymphocytes leave the bone marrow to mature in the thymus
• Mature T-lymphocytes have specific cell surface receptors called T cell receptors
• These receptors have a similar structure to antibodies and are each specific to one antigen

Question 17

T-lymphocytes are activated when they

Answer 17

encounter (and bind to) their specific antigen that is being presented by one of the host’s cells (host cells being the human’s own cells)

-This antigen-presenting host cell might be a macrophage or a body cell that has been invaded by a pathogen and is displaying the antigen on its cell surface membrane

Question 18

These activated T-lymphocytes (those that have receptors specific to the antigen) divide

Answer 18

by mitosis to increase in number (similar to the clonal selection and clonal expansion of B-lymphocytes) and differentiate into two main types of T cell:

• Helper T cells
• Killer T cells

Question 19

Neutrophils in the blood increase in number during

Answer 19

bacterial infections and when tissues become inflamed and die

Question 20

Lymphocytes in the blood increase in number during

Answer 20

viral infections and tuberculosis

Question 21

Blood tests are regularly carried out by doctors to help them diagnose

Answer 21

diseases and assess the success of treatments

-The numbers of different types of white blood cells in the blood can provide information about what type of infection someone might have, the severity of the infection, or whether the treatment that has been prescribed is working

Question 22

The two groups of stem cells in the bone marrow are:

Answer 22

• Myeloid stem cells – differentiate to form red blood cells, neutrophils, monocytes and platelets
• Lymphoid stem cells – differentiate to form lymphocytes (both B-lymphocytes and T-lymphocytes)
• These stem cells divide in a rapid but controlled way, producing very large numbers of differentiated white blood cells that carry out specific functions within an immune response

Question 23

Leukaemia

Answer 23

• Leukaemias are cancers of these bone marrow stem cells
• When someone has leukaemia, these stem cells divide rapidly but uncontrollably, producing large numbers of cells that do not differentiate properly (known as malignant cells) and therefore do not function appropriately
• The malignant cells also fill the bone marrow and disrupt the production of normal blood cells (including red blood cells and platelets). They then enter the blood and the lymphatic system

Question 24

There are two types of leukaemia, each having a slightly different effect:

Answer 24

• Myeloid leukaemias
• Lymphoblastic leukaemias

Question 25

Myeloid leukaemias

Answer 25

neutrophil-producing stem cells divide rapidly and uncontrollably (number of immature neutrophil cells increases)

Question 26

Lymphoblastic leukaemias are

Answer 26

– lymphocyte-producing stem cells divide rapidly and uncontrollably (number of immature lymphocyte cells increases)

Question 27

Myeloid and lymphoblastic leukaemias can take two forms:

Answer 27

• Acute form – acute leukaemias develop rapidly, have severe effects and must be treated as soon as a diagnosis is made
• Chronic form – chronic leukaemias develop slowly (some take many years) and changes in blood cell counts are monitored over time so that treatment can be given when it has the highest chance of curing the disease

Question 28

immature white blood cells disrupt the balance of components in the blood: in what way

Answer 28

• The number of red blood cells or platelets decreases, resulting in anaemia and an increased risk of excessive bleeding
• The number of mature neutrophils and lymphocytes decreases, resulting in immunosuppression (increased susceptibility to infections)

Question 29

antigens

Answer 29

• Every cell in the human body has markers that identify it
• Microorganisms (both pathogenic and non-pathogenic), such as bacteria and viruses, also have their own unique markers
• they allow cell-to-cell recognition
• Antigens are found on cell surface membranes, bacterial cell walls, or the surfaces of viruses
• Some glycolipids and glycoproteins on the outer surface of cell surface membranes act as antigens

Question 30

Antigens produced by the organism’s own body cells (those that the immune system does not recognise as foreign antigens)

Answer 30

are known as self antigens

-Self antigens do not stimulate an immune response

Question 31

Antigens not produced by the organism’s own body cells (those that the immune system recognises as being foreign eg. the antigens found on pathogenic bacteria and viruses or if a person receives a different blood type during a transfusion) are known as

Answer 31

• non-self antigens
• Non-self antigens stimulate an immune response

Question 32

During an immune response, B-lymphocytes form two types of cell:

Answer 32

plasma cells and memory cells

Question 33

Memory cells form the basis of

Answer 33

immunological memory – the cells can last for many years and often a lifetime

Question 34

There are two types of immune response:

Answer 34

• Primary immune response (responding to a newly encountered antigen)
• Secondary immune response (responding to a previously encountered antigen)

Question 35

Primary immune response

Answer 35

• When an antigen enters the body for the first time, the small numbers of B-lymphocytes with receptors complementary to that antigen are stimulated to divide by mitosis
• As these clones divide repeatedly by mitosis (the clonal expansion stage) the result is large numbers of identical B-lymphocytes being produced over a few weeks
• Some of these B-lymphocytes become plasma cells that secrete lots of antibody molecules (specific to the antigen) into the blood, lymph or linings of the lungs and the gut
• These plasma cells are short-lived (their numbers drop off after several weeks) but the antibodies they have secreted stay in the blood for a longer time
• The other B-lymphocytes become memory cells that remain circulating in the blood for a long time
• This response to a newly encountered pathogen is relatively slow

Question 36

clonal selection

Answer 36

When an antigen enters the body for the first time, the small numbers of B-lymphocytes with receptors complementary to that antigen are stimulated to divide by mitosis

Question 37

Secondary immune response

Answer 37

• If the same antigen is found in the body a second time, the memory cells recognise the antigen, divide very quickly and differentiate into plasma cells (to produce antibodies) and more memory cells
• This response is very quick, meaning that the infection can be destroyed and removed before the pathogen population increases too much and symptoms of the disease develop
• This response to a previously encountered pathogen is, relative to the primary immune response, extremely fast

Question 38

T-lymphocytes also play a part in the secondary immune response

Answer 38

They differentiate into memory cells, producing two main types:

• Memory helper T cells
• Memory killer T cells
• Just like the memory cells formed from B-lymphocytes, these memory T cells remain in the body for a long time
• If the same antigen is found in the body a second time, these memory T cells become active very quickly

Question 39

The effect of Myasthenia gravis at a neuromuscular junction

Answer 39

Question 40

autoimmune diseases:

Answer 40

• Autoimmune disease occur because the body’s immune system attacks one or more self antigens (antigens that are produced by human body cells)
• During the maturation of T cells, many of the T cells are destroyed because they have incorrect T cell receptors that are complementary to self-antigens (these T cell surface receptors should only be complementary to non-self antigens)
• However, some of these incorrect T cells evade destruction and become activated to stimulate an immune response against these self-antigens (ie. against the body itself)
• This starts an attack (usually involving antibodies and killer T cells) against the body
• In some autoimmune diseases, this attack is localised and directed against one organ (eg. Type 1 diabetes). In others, it is directed against the whole body (eg. lupus)

Question 41

Myasthenia gravis (MG)

Answer 41

• That targets the neuromuscular junctions between motor neurones (nerve cells) and skeletal muscle cells
• That causes the immune system to block receptor proteins at the neuromuscular junction (antibodies are produced, which then bind to these receptor proteins, blocking the transmission of impulses from motor neurons)
• Where muscles fibres absorb the receptor-antibody complexes and destroy them
• That results in non-functioning receptors which results in muscle cells receiving no stimulation and can lead to muscle tissue starting to break down

Question 42

Myasthenia gravis (MG) meaning

Answer 42

grave (serious) muscle weakness, is an autoimmune disease: