4.1 - Communicable diseases Flashcards
Malaria
- Cause by protoctists: Plasmodium vivid
- Carried by vector - female Anopheles mosquito
- Can also be transmitted by: blood transfusions and across the placenta
Life cycle
- Person with malaria - has gametes of P. vivax in blood
- Person bitten by female Anopheles mosquito and gametes in blood go into its stomach
- Gametes fuse and zygotes of P.vivax develop in stomach
- These develop into infective stages and migrate to salivary glands of mosquito
- Mosquito bites uninfected person and injects in some of its saliva containing infective P.vivax
- Infective stages of P.vivax enter new host’s liver and divide (by mitosis
- These enter the blood to feed on haemoglobin in red blood cells and
make more gametes in the process
HIV - human immunodeficiency virus/ AIDS - acquired immune deficiency disease
- HIV causes AIDS
- HIV positive = inactive version of virus present (no symptoms of AIDS) -
can go unknown for a long time (during which time it can be transmitted) - Active version of virus destroys T helper cells
- Lowers ability to destroy pathogens
- Increased likelihood of contracting (AIDS related) diseases e.g. pneumonia
Phagocytosis (non-specific immune response)
- Phagocytes - engulf and digest pathogens
- receptor on phagocyte’s cell surface membrane binds to antigen on pathogen’s cell surface membrane
- pathogen engulfed by endocytosis
- this produces a phagosome (phagocytic vesicle)
- lysosomes fuse with phagosome, releasing enzymes (lysins) into it
- the pathogen is digested into amino acids and fatty acids etc
- products are absorbed into cytoplasm by diffusion
Structure and function of antibodies
4 polypeptide chains held together by disulphide bonds. Y shaped molecule
Constant region = For binding to phagocytes
Variable region - complementary in shape to antigen = Binds to antigens
More than one variable region = Allows attachment to more than one antigen (hence attaching to more than one pathogen - agglutination)
Hinge region = Allows flexibility for the branches of the Y shaped molecule to move closer/further apart to bind to more than one antigen
The roles of antibodies
- antibodies bind to antigens on pathogen
- neutralisation of pathogens
- antibodies cover binding sites on pathogen
- which prevents their entry to host cell
- agglutination of pathogens
- multiple variable regions allows antibodies to clump/bind together many pathogens
- clump too large to enter host cell and increases likelihood of being consumed by (named)
phagocyte
Immune response – T lymphocytes (cellular response)
- Macrophages engulf and digest pathogens incorporate pathogen’s antigens into their own cell
surface membrane - they are now antigen presenting cells - This helps to select the right specific T lymphocytes with receptors complementary in shape to the antigens - clonal selection
- Once the correct T lymphocytes are selected, they can carry divide by mitosis in clonal expansion
- T helper cells release cytokines with specific shapes which bind to complementary receptors on the cell surface membrane of B lymphyocytes, stimulating them to divide by mitosis and
differentiate. They also stimulate macrophages to carry out more phagocytosis - T killer cells kill infected host cells by secreting protease enzymes into them
- T memory cells stay in the blood in case there is a secondary infection by the same pathogen. They allow a faster secondary response because they recognise the antigen and can make clones and differentiate to form new T cells more quickly than in the primary response
The changes and roles of B Lymphocytes in an immune response (humoral response)
- Specific B lymphocytes with receptors complementary in shape to the antigens on the invading pathogen are selected - clonal selection
- Cytokines released by T helper cells stimulate the B lymphocytes to divide by mitosis in clonal
expansion and then to differentiate into plasma cells and B memory cells. - Plasma cells which produce and secrete antibodies which are complementary in shape to the
antigen. These can cause the agglutination or neutralisation of the pathogens. - B memory cells stay in the blood in case there is a secondary infection by the same pathogen. They allow a faster secondary response because they recognise the antigen and can make clones and change to form new plasma cells and so antibodies are made more quickly than in the primary response
Examples of cell signalling in the immune response
- Pathogens antigens communicate to body cells that they are foreign
- Infected with foreign antigens on surface communicate to lymphocytes to be selected in clonal
selection and to T killer cells that they need to be killed - Macrophages engulf and digest pathogens and incorporate the pathogen’s antigens on their cell surface membrane - communicates to T lymphocytes to be selected in clonal selection
- T helper cells release cytokines - bind to receptors on B cells and stimulate them divide by mitosis and differentiate
Primary and secondary immune response
Primary response - first infection:
- there is a time delay to trigger immune response after first infection
- no B memory cells - slow antibody production and few produced
Secondary response:
- has a shorter delay before response. The response is much quicker.
- B memory cells specific to the antigen of the pathogen have remained in the blood after being
produced in the primary response. They can clone and differentiate to make plasma cells which make more antibodies much more quickly. They give immunity to a disease.
Groups of people who should be immunised
- Elderly/young children
- Weak immune systems/young children have had little time to build up natural immunity to
many diseases - People with HIV/AIDs
- Weak immune systems so can’t produce many antibodies themselves
- Pregnant women
- Foetus has undeveloped immune system
- Health workers
- More likely to be at risk of getting a disease
- People with chronic disease like TB or autoimmune disease
- Already in poor health and their bodies may be unable to withstand further disease
Why some people choose not to get immunised
- too busy/can’t be bothered to go to the doctors
- media scare stories
- concerned about side effects
- allergic to vaccine
- fear of needles
- religious reasons
- cost of vaccine is too expensive
Why governments want people to be vaccinated aside from the direct health benefits
- prevention of disease can save days lost at work by many people -which could harm the
economy - it costs less to immunise many people than it would to treat them
- the health service may not be able to cope if large numbers of people became infected
Why are the elderly (and others) encouraged to get a vaccine for the influenza virus every year
- vaccine is changed every year
- as there are different strains of the virus each year as it has mutated from the previous year
- new strains have different antigens
- the old antibodies from the previous year aren’t complementary to the new antigen and the new vaccination will encourage the new antibodies to be made
How governments go about vaccinating people to control a disease
Herd vaccination
- vaccinate all people at risk
- stops infection spreading
Ring vaccination
- requires people to report victims
- vaccinate all people living with or near victim
- contains spread within ring
Why it has not been possible to produce an effective vaccine for malaria
- there are different strains of the protoctist each year as it has mutated from the previous year
- new strains have different antigens
- more than one stage in its life cycle and different stages have different antigens and would require different vaccines
- the Plasmodium is concealed in liver cells and RBCs so it is only exposed to the immune system
for a short period of time
