Module 4: Section 1 - Disease and the Immune System Flashcards
Define direct transmission and give several examples
Direct transmission is when a disease is transmitted directly from one organism to another. Examples include droplet infection (coughing or sneezing tiny droplets of mucus or saliva directly onto someone, sexy times or touching an infected organism
EXAMPLE: HIV can be transmitted through the sexytimes and athletes foot can be transmitted via touch
Define indirect transmission and give several examples
Indirect transmission is when a disease is transmitted from one organism to another through an intermediate. Intermediates include air, water, food or a vector
What three factors affect disease transmission?
Living conditions, climate and social factors
How do living conditions affect disease transmission and give an example?
Overcrowded living conditions increase the transmission of many communicable diseases.
E.g. TB is spread directly via droplet infection. It’s also spread indirectly because the bacteria can remain in the air for long periods of time and infect new people. The risk of TB infection is increased when lots of people live crowded together in a small space.
How does climate affect disease transmission and give an example?
Potato/tomato late blight is especially common during wet summers because the spores need water to spread.
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/
How can social factors increase the transmission of communicable diseases and give an 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. condoms
How does skin act as a primary, non-specific immune defense?
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.
How do mucous membranes act as a primary, non-specific immune defense?
Mucous membranes - these protect body openings that are exposed to the environment. Some membranes secrete mucus - a sticky substance that traps pathogens and contains antimicrobial enzymes.
How does blood clotting act as a primary, non-specific immune defense?
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.
How does inflammation act as a primary, non-specific immune defense?
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, 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.
How does wound repair act as a primary, non-specific immune defence?
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.
What three physical defences to plants have against pathogens and why are these defences effective?
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.
Plants don’t just rely on physical defenses. They also produce antimicrobial chemicals which kill pathogens or inhibit their growth. Give two 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.
Other chemicals secreted by plants are toxic to insects - what does this mean?
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.
Foreign antigens trigger an immune response. Summarise briefly the three steps involved.
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.
What are the four main stages in the immune response?
1) phagocytes engulf pathogens
2) phagocytes activate T lymphocytes
3) T lymphocytes activate B lymphocytes, which divide into plasma cells
4) plasma cells make more antibodies to a specific antigen
A phagocyte is a type of white blood cell that carries out phagocytosis. They’re found in the blood and in tissues and carry out a non-specific immune response. Give the 5 steps in how they work.
1) a phagocytes 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 fuses with the phagosome. The enzymes break down the pathogen
5) 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).
How do opsonins work?
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.
What are neutrophils and what do they do?
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.
The second stage in the immune response is: phagocytes activate T lymphocytes. Give the seven steps in which this happens.
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.
