Disease and the immune system Flashcards

Question

How does climate affect disease transmission?

Answer 1

2) Climate can also affect the spread of communicable diseases. Examples: • Potato/tomato late blight is especially common during wet summers because the spores need water to spread (see previous page). • Malaria is most common in tropical countries, which are humid and hot. This is because these are the ideal conditions for mosquitoes (the malaria vectors) to breed.

Answer 2

3) In humans, social factors can increase the transmission of communicable diseases. Example: The risk of HIV infection is high in places where there’s limited access to: • good healthcare — people are less likely to be diagnosed and treated for HIV, and the most effective anti-HIV drugs are less likely to be available, so the virus is more likely to be passed on to others. • good health education — to inform people about how HIV is transmitted and how it can be avoided, e.g. through safe-sex practices like using condoms.

Answer 3

enter an organism

Answer 4

``` skin mucous membranes blood clotting inflammation wound repair expulsive reflexes ```

Answer 5

Skin — this acts as a physical barrier, blocking pathogens from entering the body. It also acts as a chemical barrier by producing chemicals that are antimicrobial and can lower pH, inhibiting the growth of pathogens.

Answer 6

Mucous membranes — these protect body openings that are exposed to the environment (such as the mouth, nostrils, ears, genitals and anus). Some membranes secrete mucus — a sticky substance that traps pathogens and contains antimicrobial enzymes.

Answer 7

Blood clotting — a blood clot is a mesh of protein (fibrin) fibres. Blood clots plug wounds to prevent pathogen entry and blood loss. They’re formed by a series of chemical reactions that take place when platelets (fragments of cells in the blood) are exposed to damaged blood vessels.

Answer 8

Inflammation — the signs of inflammation include swelling, pain, heat and redness. It can be triggered by tissue damage — the damaged tissue releases molecules, which increase the permeability of the blood vessels, so they start to leak fluid into the surrounding area. This causes swelling and helps to isolate any pathogens that may have entered the damaged tissue. The molecules also cause vasodilation (widening of the blood vessels), which increases blood flow to the affected area. This makes the area hot and brings white blood cells to the area to fight off any pathogens that may be present.

Answer 9

Wound repair — the skin is able to repair itself in the event of injury and re-form a barrier against pathogen entry. The surface is repaired by the outer layer of skin cells dividing and migrating to the edges of the wound. The tissue below the wound then contracts to bring the edges of the wound closer together. It is repaired using collagen fibres — too many collagen fibres and you’ll end up with a scar.

Answer 10

Expulsive reflexes — e.g. coughing and sneezing. A sneeze happens when the mucous membranes in the nostrils are irritated by things such as dust or dirt. A cough stems from irritation in the respiratory tract. Both coughing and sneezing are an attempt to expel foreign objects, including pathogens, from the body. They happen automatically.

Answer 11

Physical and chemical defences

Answer 12

1) Most plant leaves and stems have a waxy cuticle, which provides a physical barrier against pathogen entry. It may also stop water collecting on the leaf, which could reduce the risk of infection by pathogens that are transferred between plants in water. 2) Plant cells themselves are surrounded by cell walls. These form a physical barrier against pathogens that make it past the waxy cuticle. 3) Plants produce a polysaccharide called callose. Callose gets deposited between plant cell walls and plasma membranes during times of stress, e.g. pathogen invasion. Callose deposition may make it harder for pathogens to enter cells. Callose deposition at the plasmodesmata (small channels in the cell walls) may limit the spread of viruses between cells.

Answer 13

1) Plants don’t just rely on physical defences. They also produce antimicrobial chemicals (including antibiotics) which kill pathogens or inhibit their growth. Examples: • Some plants produce chemicals called saponins. These are thought to destroy the cell membranes of fungi and other pathogens. • Plants also produce chemicals called phytoalexins, which inhibit the growth of fungi and other pathogens. 2) Other chemicals secreted by plants are toxic to insects — this reduces the amount of insect-feeding on plants and therefore reduces the risk of infection by plant viruses carried by insect vectors.

Answer 14

1) Antigens are molecules (usually proteins or polysaccharides) found on the surface of cells.

Answer 15

1) Antigens are molecules (usually proteins or polysaccharides) found on the surface of cells. 2) When a pathogen (like a bacterium) invades the body, the antigens on its cell surface are identified as foreign, which activates cells in the immune system. 3) The immune response involves specific and non-specific stages. The non-specific response happens in the same way for all microorganisms — whatever foreign antigens they have. The specific response is antigen-specific — it is aimed at specific pathogens. It involves white blood cells called T and B lymphocytes.

Answer 16

phagocytes engulf pathogens phagocytes activate T lymphocytes T lymphocytes activate B lymphocytes which divides into plasma cells plasma cells make more antibodies to a specific antigen

Answer 17

A phagocyte is a type of white blood cell that carries out phagocytosis (engulfment of pathogens). They’re found in the blood and in tissues and carry out a non-specific immune response. Here’s how they work:

Answer 18

1) A phagocyte recognises the antigens on a pathogen. 2) The cytoplasm of the phagocyte moves round the pathogen, engulfing it. This may be made easier by the presence of opsonins— molecules in the blood that attach to foreign antigens to aid phagocytosis. 3) The pathogen is now contained in a phagosome (a type of vesicle) in the cytoplasm of the phagocyte. 4) A lysosome (an organelle that contains digestive enzymes) fuses with the phagosome. The enzymes break down the pathogen. The phagocyte then presents the pathogen’s antigens. It sticks the antigens on its surface to activate other immune system cells. When a phagocyte does this it is acting as an antigen-presenting cell (APC).

Answer 19

``` Opsonins work in different ways. Some hide the negative charges on the membrane of the pathogen, making it easier for the negatively-charged phagocyte to get closer to the pathogen. ```

Answer 20

Neutrophils are a type of phagocyte. They’re the first white blood cells to respond to a pathogen inside the body. Neutrophils move towards a wound in response to signals from cytokines (proteins that act as messenger molecules). The cytokines are released by cells at the site of the wound.

Answer 21

1) A T lymphocyte is another type of white blood cell.

Answer 22

1) A T lymphocyte is another type of white blood cell.2) Their surface is covered with receptors. 3) The receptors bind to antigens presented by APCs. 4) Each T lymphocyte has a different receptor on its surface. 5) When the receptor on the surface of a T lymphocyte meets a complementary antigen, it binds to it — so each T lymphocyte will bind to a different antigen. 6) This activates the T lymphocyte — the process is called clonal selection. 7) The T lymphocyte then undergoes clonal expansion — it divides to produce clones of itself. Different types of T lymphocytes carry out different functions — see next page.

Answer 23

1) T helper cells 2) T killer cells 3) T regulatory cells

Answer 24

1) T helper cells — these release substances to activate B lymphocytes and T killer cells.

Answer 25

2) T killer cells — these attach to and kill cells that are infected with a virus.

Answer 26

3) T regulatory cells — these suppress the immune response from other white blood cells. This helps to stop immune system cells from mistakenly attacking the host’s body cells.

Answer 27

1) B lymphocytes are another type of white blood cell. 2) They’re covered with proteins called antibodies. 3) Antibodies bind to antigens to form an antigen-antibody complex. 4) Each B lymphocyte has a different shaped antibody on its surface. 5) When the antibody on the surface of a B lymphocyte meets a complementary shaped antigen, it binds to it — so each B lymphocyte will bind to a different antigen. 6) This, together with substances released from T helper cells, activates the B lymphocyte. This process is another example of clonal selection. 7) The activated B lymphocyte divides, by mitosis, into plasma cells and memory cells. This is another example of clonal expansion

Answer 28

1) Cell signalling is basically how cells communicate. 2) A cell may release (or present) a substance that binds to the receptors on another cell — this causes a response of some kind in the other cell. 3) Cell signalling is really important in the immune response because it helps to activate all the different types of white blood cells that are needed. 4) For example, T helper cells release interleukins (a type of cytokine) that bind to receptors on B lymphocytes. This activates the B lymphocytes — the T helper cells are signalling to the B lymphocytes that there’s a pathogen in the body.

Answer 29

1) Plasma cells are clones of the B lymphocyte (they’re identical to the B lymphocyte). 2) They secrete loads of the antibody, specific to the antigen, into the blood. 3) These antibodies will bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes.

Answer 30

DRAWING ON OTHER FLASHCARD!!!! • Antibodies are glycoproteins made of four polypeptide chains — two heavy chains and two light chains. Each chain has a variable region and a constant region. • The variable regions of the antibody form the antigen binding sites. The shape of the variable region is complementary to a particular antigen. The variable regions differ between antibodies. • The hinge region allows flexibility when the antibody binds to the antigen. • The constant regions allow binding to receptors on immune system cells, e.g. phagocytes. The constant region is the same (i.e. it has the same sequence of amino acids) in all antibodies. • Disulfide bridges (a type of bond) hold the polypeptide chains of the protein together.

Answer 31

1) Agglutinating pathogens 2) Neutralising toxins 3) Preventing the pathogen binding to human cells

Answer 32

1) Agglutinating pathogens — each antibody has two binding sites, so an antibody can bind to two pathogens at the same time — the pathogens become clumpedtogether. Phagocytes then bind to the antibodies and phagocytose a lot of pathogens all at once. Antibodies that behave in this way are known as agglutinins.

Answer 33

2) Neutralising toxins — like antigens, toxins have different shapes. Antibodies called anti-toxins can bind to the toxins produced by pathogens. This prevents the toxins from affecting human cells, so the toxins are neutralised (inactivated). The toxin-antibody complexes are also phagocytosed.

Answer 34

3) Preventing the pathogen binding to human cells — when antibodies bind to the antigens on pathogens, they may block the cell surface receptors that the pathogens need to bind to the host cells. This means the pathogen can’t attach to or infect the host cells.

Answer 35

1) When a pathogen enters the body for the first time, the antigens on its surface activate the immune system. This is called the primary response. 2) The primary response is slow because there aren’t many B lymphocytes that can make the antibody needed to bind to it. 3) Eventually the body will produce enough of the right antibody to overcome the infection. Meanwhile the infected person will show symptoms of the disease. 4) After being exposed to an antigen, both T and B lymphocytes produce memory cells. These memory cells remain in the body for a long time. 5) Memory T lymphocytes remember the specific antigen and will recognise it a second time round. Memory B lymphocytes record the specific antibodies needed to bind to the antigen. 6) The person is now immune — their immune system has the ability to respond quickly to a second infection.

Answer 36

1) If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response — the secondary response. 2) Clonal selection happens faster. Memory B lymphocytes are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T lymphocytes are activated and divide into the correct type of. T lymphocytes to kill the cell carrying the antigen. 3) The secondary response often gets rid of the pathogen before you begin to show any symptoms.

Answer 37

Primary Secondary Pathogen 1st time 2nd speed of response slow fast cells activated B + T lymphocytes Memory cells symptoms yes no

Answer 38

1) As the name suggests, a blood smear is a sample of blood smeared over a microscope slide. 2) Stains are added to the sample to make the different cells easy to see 3) When looking at a blood smear you’re likely to see red blood cells, white blood cells and platelets (tiny fragments of cells involved in blood clotting). Some types of white blood cells have granules in their cytoplasm (so they look grainy) and other types don’t.

Answer 39

red blood cells don’t have a nucleus. neutrophil. Its nucleus looks like three interconnected blobs the nucleus is ‘multi-lobed’. The cytoplasm of a neutrophil is grainy. lymphocyte. It’s much smaller than the neutrophil. The nucleus takes up most of the cell and there’s very little cytoplasm to be seen (it’s not grainy either). You can’t tell whether this is a T lymphocyte or a B lymphocyte under a light microscope. This is a monocyte. It’s the biggest white blood cell and a type of phagocyte.it has a kidney-bean shaped nucleus and a non-grainy cytoplasm.

Answer 40

active or passive

Answer 41

ACTIVE IMMUNITY This is the type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen.

Answer 42

There are two different types of active immunity

Answer 43

Natural and artificial vaccination

Answer 44

1) Natural — this is when you become immune after catching a disease. E.g. if you have measles as a child, you shouldn’t be able to catch it again in later life.

Answer 45

2) Artificial — this is when you become immune after you’ve been given a vaccination containing a harmless dose of antigen

Answer 46

This is the type of immunity you get from being given antibodies made by a different organism — your immune system doesn’t produce any antibodies of its own.

Answer 47

Again, there are two types:

Answer 48

Natural | Artificial antibodies

Answer 49

1) Natural — this is when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk.

Answer 50

2) Artificial — this is when you become immune after being injected with antibodies from someone else. E.g. If you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from blood donations.

Answer 51

Active immunity Passive immunity Requires exposure to antigen No exposure to antigen It takes a while for protection to develop Protection is immediate Protection is long-term Protection is short-term Memory cells are produced Memory cells aren’t produced

Answer 52

Abnormal immune response

Answer 53

1) Sometimes, an organism’s immune system isn’t able to recognise self-antigens — the antigens present on the organism’s own cells. 2) When this happens, the immune system treats the self-antigens as foreign antigens and launches an immune response against the organism’s own tissues. 3) A disease resulting from this abnormal immune response is known as an autoimmune disease. 4) Autoimmune diseases are usually chronic (long-term). They can often be treated, but not cured.

Answer 54

lupus | rheumatoid arthritis

Answer 55

• Lupus — caused by the immune system attacking cells in the connective tissues. This damages the tissues and causes painful inflammation (see page 100). Lupus can affect the skin and joints, as well as organs such as the heart and lungs.

Answer 56

• Rheumatoid arthritis — caused by the immune system attacking cells in the joints. Again this causes pain and inflammation.

Answer 57

1) While your B lymphocytes are busy dividing to build up their numbers to deal with a pathogen (i.e. the primary response), you suffer from the disease. Vaccination can help avoid this. 2) Vaccines contain antigens that cause your body to produce memory cells against a particular pathogen, without the pathogen causing disease. This means you become immune without getting any symptoms. 3) If most people in a community are vaccinated, the disease becomes extremely rare. This means that even people who haven’t been vaccinated are unlikely to get the disease, because there’s no one to catch it from. This is called herd immunity. It helps to prevent epidemics — mass outbreaks of disease. 4) Vaccines always contain antigens — these may be free or attached to a dead or attenuated (weakened) pathogen. 5) Sometimes booster vaccines are given later on (e.g. after several years) to make sure memory cells are produced. 6) Vaccination is not the same as immunisation. Vaccination is the administration of antigens (in a vaccine) into the body. Immunisation is the process by which you develop immunity. Vaccination causes immunisation.

Answer 58

MMR | Meningitis C vaccine

Answer 59

• the MMR — protects against measles, mumps and rubella. The MMR is usually given to children as an injection at around a year old, and again before they start school. It contains attenuated measles, mumps and rubella viruses.

Answer 60

the Meningitis C vaccine — protects against the bacteria that cause Meningitis C. It is first given as an injection to babies at 3 months. Boosters are then given to 1-year-olds and teenagers.

Answer 61

The influenza (flu) vaccine changes every year. That’s because the antigens on the surface of the influenza virus change regularly, forming new strains of the virus. 2) Memory cells produced from vaccination with one strain of the flu will not recognise other strains with different antigens. The strains are immunologically distinct. 3) Every year there are different strains of the influenza virus circulating in the population, so a different vaccine has to be made. 4) Laboratories collect samples of these different strains, and organisations, such as the WHO (World Health Organisation) and CDC (Centre for Disease Control), test the effectiveness of different influenza vaccines against them. 5) New vaccines are developed and one is chosen every year that is the most effective against the recently circulating influenza viruses. virus 6) Governments and health authorities then implement a programme of vaccination using the most suitable vaccine. Sometimes people are given a vaccine that protects them from a strain causing an epidemic in another country — this helps to stop the strain spreading globally.

Answer 62

1) Antibiotics are chemicals that kill or inhibit the growth of bacteria. 2) They’re used by humans as drugs to treat bacterial infections. They’re useful because they can usually target bacterial cells without damaging human body cells. 3) Penicillin was the first antibiotic to be isolated (by Alexander Fleming, in 1928). 4) Antibiotic use became widespread from the mid-twentieth century — partly thanks to the successful treatment of soldiers with penicillin in the Second World War. 5) For the past few decades, we’ve been able to deal with bacterial infections pretty easily using antibiotics. As a result of this, the death rate from infectious bacterial disease has fallen dramatically. 6) Despite their usefulness, there are risks to using antibiotics. For example, they can cause side effects and even severe allergic reactions in some people. Perhaps the biggest risk though, is from antibiotic resistance...

Answer 63

1) There is genetic variation in a population of bacteria. Genetic mutations make some bacteria naturally resistant to an antibiotic. 2) For the bacterium, this ability to resist an antibiotic is a big advantage. It’s better able to survive, even in a host who’s being treated with antibiotics to get rid of the infection, and so it lives for longer and reproduces many more times. 3) This leads to the allele for antibiotic resistance being passed on to lots of offspring. It’s an example of natural selection — see page 127. This is how antibiotic resistance spreads and becomes more common in a population of bacteria over time. 4) This is a problem for people who become infected with these bacteria, because you can’t easily get rid of them with antibiotics. 5) Increased use of antibiotics means that antibiotic resistance is increasing. Superbugs’ that are resistant to most known antibiotics are becoming more common. This means we are less able to treat some potentially life-threatening bacterial infections.

Answer 64

MRSA | Clostridium difficile

Answer 65

• MRSA (meticillin-resistant Staphylococcus aureus) causes serious wound infections and is resistant to several antibiotics, including meticillin (which used to be called methicillin).

Answer 66

• Clostridium difficile infects the digestive system, usually causing problems in people who have already been treated with antibiotics. It is thought that the harmless bacteria that are normally present in the digestive system are killed by the antibiotics, which C. difficile is resistant to. This allows C. difficile to flourish. C. difficile produces a toxin, which causes severe diarrhoea, fever and cramps

Answer 67

Developing new antibiotics and modifying existing ones are two ways of overcoming the current problem of antibiotic resistance. This isn’t easy though. To reduce the likelihood of antibiotic resistance developing in the first place, doctors are being encouraged to reduce their use of antibiotics, e.g. not to prescribe them for minor infections and not to prescribe them to prevent infections (except in patients with already weak immune systems, e.g. the elderly or people with HIV). Patients are advised to take all of the antibiotics they’re prescribed to make sure the infection is fully cleared and all the bacteria have been killed (which reduces the likelihood of a population of antibiotic-resistant bacteria developing).

Answer 68

1) Many medicinal drugs are manufactured using natural compounds found in plants, animals or microorganisms. E.g. penicillin is obtained from a fungus, some cancer drugs are made using soil bacteria, and daffodils are now grown to produce a drug used to treat Alzheimer’s disease. 2) Only a small proportion of organisms have been investigated so far, so it’s possible that plants or microorganisms exist that contain compounds that could be used to treat currently incurable diseases, such as AIDS. Others may produce new antibiotics. 3) Possible sources of drugs need to be protected by maintaining the biodiversity (the variety of different species) on Earth. If we don’t protect them, some species could die out before we get a chance to study them. 4) Even organisms that have already been studied could still prove to be useful sources of medicines as new techniques are developed for identifying, purifying and testing compounds.

Answer 69

1) Your genes determine how your body responds to certain drugs. Different people respond to the same drug in different ways — which makes certain drugs more effective for some people than others. This is where personalised medicines come in. 2) Personalised medicines are medicines that are tailored to an individual’s DNA. The theory is that if doctors have your genetic information, they can use it to predict how you will respond to different drugs and only prescribe the ones that will be most effective for you. 3) Scientists hope that by studying the relationship between someone’s genetic make-up and their responsiveness to drugs, can be produced in the future.

Answer 70

1) Synthetic biology involves using technology to design and make things like artificial proteins, cells and even microorganisms. 2) It has applications in lots of different areas, including medicine. For example, scientists are looking at engineering bacteria to destroy cancer cells, while leaving healthy body cells intact.

Disease and the immune system Flashcards

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