4.1.1 Disease and the Immune System Flashcards
What is a disease?
- a condition that impairs the normal functioning of an organism
What is a pathogen?
- a disease-causing organism
- can be bacteria, fungi, viruses and protoctista
What is a communicable disease
- a disease that can be spread between organisms
- aka infection disease
What causes tuberculosis and what does it affect?
- bacterium
- animals, typically animals and cattle
What causes bacterial meningitis and what does it affect?
- bacterium
- humans
What causes ring rot and what does it affect?
- bacterium
- potatoes, tomatoes
What causes HIV/AIDS and what does it affect?
- virus
- humans
What causes influenza and what does it affect?
- virus
- animals
What causes tobacco mosaic virus and what does it affect?
- virus
- plants
What causes black sigatoka and what does it affect?
- fungus
- banana plants
What causes ringworm and what does it affect?
- fungus
- cattle
What causes athlete’s foot and what does it affect?
- fungus
- humans
What causes potato/tomato late blight and what does it affect?
- protoctist
- potatoes and tomatoes
What causes malaria and what does it affect?
- protoctist
- animals
What is direct transmission?
- when a disease is transmitted directly from one organism to another
give examples of direct transmission
- direct physical contact
- droplet infection
- sexual intercourse
- transmission by spores
- faecal
What is indirect transmission?
- when a disease is transmitted from one organism to another via an intermediate
Give examples of indirect transmission
- intermediates such as
- air
- water
- food
- vector (another organism)
What three factors affect disease transmission?
- overcrowding: living condition increase transmission of many communicable diseases
e. g. TB is spread directly via droplet infection - climate:
e. g. potato/tomato late blight is common during wet summers because spores need water to spread
e. g. malaria because ideal for mosquito - humans, social factors:
e. g. healthcare and education - poor ventilation
- homelessness
Give examples of the primary non-specific defences to prevent pathogens entering an organism
- skin
- mucous membranes
- blood clotting
- inflammation
- wound repair
- expulsive reflexes
Explain how skin acts as a primary, non-specific defence
- physical barrier, blocking pathogens from entering the body
- acts as a chemical barrier by producing chemicals that are antimicrobial and can lower pH, inhibiting growth of pathogens
Explain how mucous membranes acts as a primary, non-specific defence
- these protect body openings that are exposed to environment such as mouth, nostrils, ears, anus etc
- goblet cells secrete mucous
- mucus lines the passages and traps any pathogens
- epithelium also has militated cells
- they move the mucus to the top of the trachea, where it enter the oesophagus
- it is swallowed and passes down the digestive system
- this is killed by stomach and pathogen’s enzyme denatured
Explain how blood clotting acts as a primary, non-specific defence
- a blood clot is a mesh of 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 are exposed to damaged blood vessels
Explain how inflammation acts as a primary, non-specific defence
- include swelling, pain, heat and redness
- can be triggered by tissue damage, as it releases molecules, increasing permeability of blood vessels, leaking fluid and causing swelling
- molecules also cause vasodilation, which increases blood flow
- makes area hot and brings white blood cells to the area to fight off any pathogens
Explain how wound repair acts as a primary, non-specific defence
- surface is repaired outer layer of skin dividing and migrating to the edges of the wound
- tissues below the wound then contract to being edges of the wound closer together
- repaired using collagen fibres
- scar formed when too many collagen fibres
Explain how expulsive reflexes acts as a primary, non-specific defence
- e.g. coughing and sneezing
- attempts to expel foreign objects, including pathogens
- occurs automatically
Describe physical defences plants have
- leaves and stems have a waxy cuticle, which provides a physical barrier against pathogen entry
- may also stop water collecting on the lead, reduces risk of infection that are transferred between plants in water
- plants are surrounded by cell wall
- forms a physical barrier against pathogens that makes it past the waxy cuticle
- plants produce a polysaccharide called callose
- callose gets deposited between plant cell walls and plasma membranes during times of stress
- callose deposition may make it harder for pathogens to enter cells
- callose deposiition at the plasmodesmata may limit the spread of viruses between cells
Describe chemical defences plants have
- antimicrobial chemicals that kill pathogens or inhibit their growth
e. g. saponins: destroy cell membranes of fungi and other pathogens
e. g. phytoalexins: inhibit growth of fungi - other chemicals are toxic to insects: reduces the amount of insect-feeding on plants,
reduces infection by plant viruses carried by insect vectors
What are antigens?
- antigens are molecules, usually proteins or polysaccharides, found on the surface of cells
What is the difference between non-specific and specific immune responses?
- non specific happens the same way for all microorganism
- specific is antigen specific, involving t and B lymphocytes
What are the four main stages in the immune response?
- phagocytes engulf pathogens
- phagocytes activate T lymphocytes
- T lymphocytes activates B lymphocytes, which divide into plasma cells
- Plasma cells make more antibodies to a specific antigen
Describe the first stage in the immune response
- a phagocyte recognises the antigens on a pathogen
- the cytoplasm of the phagocyte moves round the pathogen, engulfing it
- this may be made easier by the presence of opsonins, molecules that attach to foreign antigens to aid phagocytosis
- the pathogen is now contained in a phagosome, a type of vesicle in the cytoplasm of the phagocyte
- a lysosome fuses with the phagosome, and the enzymes break down the pathogen
- the phagosome then presents the pathogen’s antigens
- it sticks the antigens on its surface to active other immune system cells
- this is known as an antigen-presenting cell (APC)
What is a phagocyte?
- a phagocyte is a type of white blood cell that carries out phagocytosis (engulfment of pathogens)
- found in blood and in tissues and carry out a non-specific immune response
What are neutrophils?
- a type of phagocyte
- first white blood cells to respond to a pathogen inside the body
- neutrophils move towards a wound in response to signals from cytokines, which are released by cells at the site of the wound
Describe stage two of the immune response
- a T lymphocyte is another type of white blood cell
- surface is covered with receptors
- receptors bind to antigens presented by APCs
- each T lymphocyte has a a different receptor on its surface
- 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
- this activates the T lymphocyte, called clonal selection
- then the T lymphocyte undergoes clonal expansion
What are the different types of activated T lymphocytes (stage 2)?
- T helper cells: release substances to activate B lymphocytes and T killer cells
- T killer cells: attach to and kill cells that are infected with a virus
- T regulatory cells: suppress the immune response from other white blood cells
- some become memory cells
Describe the third stage of the immune response
- B lymphocytes are another type of blood cell
- they’re covered with proteins called antibodies
- antibodies bind to antigens to form an antigen-antibody complex
- each B lymphocyte has a different shaped antibody on its surface
- when the antibody on the surface meets a complementary shaped antigen, it binds to
- together with substances from T helper cells activates the B lymphocyte
- this is another example of clonal selection
- the activated B lymphocytes divides, by mitosis into plasma cells and memory cells
- this is called clonal expansion
What is cell signalling (stage 3)?
- how cells communicate
- a cell may release a substance that binds to the receptors on another cell
- really important in the immune response because it helps to activate all the different types of white blood cells needed
- e.g. t helper cells release interleukins (a type of cytokine_ that bind to receptors of B lymphocytes
- activates B lymphocytes
Describe stage four of the immune response
- plasma cells are clones of the B lymphocyte
- they secrete loads of antibody’s specific to the antigen into the blood
- this will from a lot of antigen-antibody complexes
Describe the structure of an antibody
- variable region: form the antigen binding sites
- the shape of the variable region is complementary to a particular antigen. differs between antibodies
-hinge region: allows flexibility when the antibody binds to the antigen
- constant regions: allow binding to the receptors on immune system cells. constant region is the same (same sequence of amino acids) in all antibody s
- disulphide bridges hold the polypeptide chains of the protein together
How do antibodies help clear infections
- agglutinating pathogens: each antibody has two binding sites, so an antibody can bind to two pathogens at the same time, making the clumped together
- phagocytes called agglutinins then bind to the antibodies and phagocytose a lot of pathogens all at once
- neutralising toxins: 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. the toxin-antibody complexes are also phagocytose
- preventing the pathogen binding to human cells: antibodies may block the cell surface receptors that the pathogens need to bind to the host cells. meaning the pathogen can’t attach to or infect host cells
Describe why the primary response is slow
- when a pathogen enters the body for the first time, the antigens on its surface activate the immune system. this is the primary response
- the primary response is slow because there aren’t many B lymphocytes that can make the antibody needed to bind to it
- eventually the body will produce enough to overcome the infection, but showing symptoms of disease
- after exposure, both B and T lymphocytes produce memory cells, which remain in the body for a long time
- Memory T lymphocytes remember the specific antigen and will recognise it
- Memory B lymphocytes remember the specific antibodies needed to bind to the antigen
- the person is now immune
Describe the secondary response
- if the same pathogen enters again, immune system will produce a quicker, stronger immune response
- known as secondary response
- 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 antigen
- secondary response often begins before any symptoms are shown
What is active immunity?
- when your immune system makes its own antibodies after being stimulated by an antigen
What are the two different types of active immunity?
- natural: when you become immune after catching a disease
- artificial; when you become immune after vaccination
What is passive immunity?
- the type of immunity from being given antibodies made by a different organism
- immune system doesn’t produce antibodies of its own
What are the two types of passive immunity?
- natural: when a baby becomes immune due to the antibodies received from mother through placenta and breast milk
- artificial: when you become immune after being injected with antibodies from someone else
which type of immunity require exposure to antigen?
- active
which type of immunity takes a while to develop?
- active
which type of immunity has long-term protection?
- active
Which type of immunity produces memory cells?
- active
What is an autoimmune disease?
- when an organism’s immune system isn’t able to recognise self-antigens
- immune system treats the self-antigens as foreign antigens and launches an immune response on its own tissues
give examples of autoimmune diseases
- lupus: immune system attacking cells in the connective tissues. damages tissues and causes painful inflammation. affects skin, joints, organs
- rheumatoid arthritisL caused by the immune system attacking joints.
How do vaccines control disease and prevent epidemics?-
- vaccines avoid you suffering symptoms from the disease as the B lymphocytes usually have to divide to deal with pathogen
- vaccines contain antigens that cause your body to produce memory cells against a particular pathogen, without cause disease. you become immune without symptoms
- disease becomes rare if most people in a community are vaccinated. herd immunity. prevents epidemics
- vaccines always contain antigens that may be free, or attached to a dead or attenuated pathogen
- booster vaccines may be given later on to make sure memory cells are produced
Is vaccination the same as immunisation?
- no
- vaccination is the administration of antigens into the body
- immunisation is the process by which you develop immunity
- vaccination causes immunisation
Give examples of routine vaccines
- MMR
- meningitis C
Why do vaccination programmes change?
- flu vaccine changes every year because antigens on the influenza virus change regularly, forming new strains
- memory cells produced from vaccination with one strain will not recognise other strain with different antigens
- the are immunologically distinct
- a different vaccine has to be made every year
- labs such as WHO and CDC collect samples of different strains to test for effectiveness
- new vaccines developed and choose most effective
- governments choose
what are antibiotics and why are they useful?
- antibiotics are chemicals that kill or inhibit the growth of bacteria
- used by humans to treat bacterial infections
- useful because they can target bacterial cells without damaging human body cells
Describe antibiotic resistance and why it is a problem
- there is genetic mutation in a population of bacteria
- genetic mutations make some bacteria naturally resistant to an antibiotic
- the bacterium is more adapted for survival and so it lives longer and reproduces
- this leads to the allele for antibiotic resistance being passed onto offspring
- antibiotic resistance spreads and becomes more common over time
- a problem because you can’t get rid of them with antibiotics
- increased use of antibiotics means antibiotic resistance is increasing
- superbugs are becoming more common meaning we are less able to treat potentially life threatening bacteria infection
Give examples of antibiotic-resistant bacteria
- MRSA (meticillin resistant staphylococcus aureus): causes serious wound infections and is resistant to several antibiotics, including meticillin
- clostridium difficile: infects digestive system. c. difficile produces a toxin, causes fever diarrhoea and cramps
Descrive sources of medicine
- natural compounds: plants, animals and microorganisms
- only a small population of organism have been investigated so far, so perhaps many more antibiotics
- we need to protect sources of drugs by maintaining biodiversity, or it could die before studied
- using new technique to look at already studied organisms
What is the future of medicine?
- personalised medicine:
- genes determine how body responds to drugs. different people respond different, making it more effective for some than others.
- personalised medicine is tailored to an individual’s DNA. doctors may be able to predict how you will respond to different drugs and prescribe most effective
- hope more effective drugs
synthetic biology:
- using technology to design and make artificial proteins, cells and microorganisms
- e.g. engineering bacteria to destroy cancer cells