6.3/11.1 Flashcards
describe the body’s primary defence mechanism
the skin and mucous membranes form a primary defence mechanism against pathogens that cause infectious disease
skin
- outermost layer is tough and provides a physical barrier against the entry of pathogens and physical/chemical damage
- sebaceous glands are associated with hair follicles and secrete sebum, which maintains skin moisture and slightly lowering skin pH, which inhibits the growth of bacteria and fungi
mucous membranes
thinner and softer type of skin found in airways and reproductive organs
- the mucus secreted is a sticky solution of glycoproteins and traps pathogens, which are either swallowed or expelled, acting as a physical barrier
- also has antiseptic properties due to the presence of the anti-bacterial enzyme lysozyme
how are cuts in the skin sealed?
- platelets aggregate at the site forming a temporary plug
- they release clotting factors that trigger off the cascade of reactions involved in the clotting process
- this cascade results in the production of thrombin, an enzyme, which converts the soluble protein fibrinogen into the insoluble fibrin
- the resulting clot is initially a gel but if exposed to the air dries to form a hard scab
Use of phagocytes in defence
- ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to diseases
- they engulf of pathogens by endocytosis and digest them with lysosomes (enzymes)
Use of antibody production in defence
Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity
define an antigen
any chemical that stimulates an immune response
define a specific immune response
- the production of one type of antibodies specific to a particular pathogen’s antigens by lymphocytes
describe the steps of antibody production
- antigens on the pathogen stimulate cell division of the small group of lymphocytes that produce the appropriate antibody
- plasma cells (large clones of lymphocytes) are produced within a few days and secrete large quantities of the antibody
describe the role of antibodies
antibodies are large proteins that have two functional regions: a hyper variable region that binds to a specific antigen and another that helps the body fight the pathogen by
- making it more recognisable to phagocytes
- preventing viruses from docking to and entering host cells
some of the lymphocytes produced during an infection are not active plasma cells but instead become
memory cells
immunity to a disease involves
either having antibodies against the pathogens or memory cells that allow rapid production of the antibody
describe the function of antibiotics
block processes that occur in prokaryotic cells but not eukaryotic cells. For example, bacterial DNA replication, transcription, translation, ribosome function and cell wall formation.
what is the issue with widespread antibiotic use?
some strains of bacteria have evolved with genes which confer resistance to antibiotics and some strains have multiple resistance
why can viral diseases not be treated using antibiotics?
Being non-living, they rely on the host cell’s enzymes for ATP synthesis and other metabolic pathways. These processes cannot be targeted by drugs as the host cell would also be damaged.
medical name for a blood clot
thrombus
coronary thrombosis is
the formation of blood clots in the coronary arteries - this can be a fatal condition.
give 4 things that increase the risk of coronary thrombosis
coronary occlusion, damage to the capillary epithelium, hardening of the arteries, rupture of an atheroma
Effects of HIV on the immune system and modes of transmission
Production of antibodies by the immune system is a complex process and includes different types of lymphocyte, including helper T-cells. The human immunodeficiency virus (HIV) invades and destroys helper T-cells. The consequence is a progressive loss of the capacity to produce antibodies.
In the early stages of infection, the immune system makes antibodies against HIV. If these can be detected in a person’s body, they are said to be HIV-positive.
HIV is a retrovirus that has genes made of RNA and uses reverse transcriptase to make DNA copies of its genes once it has entered a host cell. The rate at which helper T-cells are destroyed by HIV varies considerably and can be slowed down by using anti-retroviral drugs. In most HIV-positive patients antibody production eventually becomes so ineffective that a group of opportunistic infections strike, which would be easily fought off by a healthy immune system.
A collection of several diseases or conditions existing together is called a syndrome. When the syndrome of conditions due to HIV is present, the person is said to have acquired immune deficiency syndrome (AIDS).
AIDS spreads by HIV infection. The virus only survives outside the body for a short time and infection normally only occurs if there is blood to blood contact between infected and uninfected people. There are various ways in which this can occur:
- sexual intercourse, during which abrasions to the mucous membranes of the penis and vagina can cause minor bleeding
- transfusion of infected blood, or blood products such as Factor VIII
- sharing of hypodermic needles by intravenous drug users.
Florey and Chain experiments
Florey and Chain tested penicillin on infected mice
Eight mice were injected with hemolytic streptococci and four of these mice were subsequently injected with doses of penicillin
The untreated mice died of bacterial infection while those treated with penicillin all survived – demonstrating its antibiotic potential
every organism has —– ——– on the surface of their cells
unique molecules
antigens on the surface of red blood cells
stimulate antibody production in a person with a different blood group
describe the presence and absence of antigens on the surface of blood cells from different blood groups
- all three alleles involve a basic antigen sequence called antigen H
A: this is modified by the addition of molecule N-acetylgalactosamine
B: additional molecule is galactose
AB: both types of antigen
O: neither surface glycoprotein
what happens if a recipient is given a transfusion involving the wrong type of blood?
an immune response occurs. antibodies are produced, agglutination (clumping) occurs, followed by hemolysis where red blood cells are destroyed and blood may coagulate in vessels
describe an immune response
- macrophage ingests pathogen and displays antigens on it
- helper T cell specific to the antigen is activated by the macrophage
- B cell specific to the antigen is activated by proteins from the helper T cell
- B cell divides repeatedly to produce antibody-secreting plasma cells
- B cell also divides to produce memory cells
- antibodies produced by the clone of plasma cells are specific to antigens on the pathogen and help destroy it
how does activation of helper T cells work?
they have an antibody-like receptor protein in their plasma membranes, which can bind to antigens displayed by macrophages
how does the structure of plasma cells relate to their function?
- the cytoplasm contains an extensive network of rough endoplasmic reticulum (rER), which manufactures, modifies, and transports proteins (antibodies).
- The range of genes expressed is lower than a typical cell as the cell produces a lot of the same protein
define clonal selection
the generation of large numbers of plasma cells that produce one specific antibody type
give and explain 4 ways in which antibodies aid the destruction of pathogens
- opsonisation- make the pathogen more recognisable to phagocytes so they are more readily engulfed. also, once bound, they can link the pathogen to phagocytes
- neutralisation of viruses and bacteria: antibodies prevent viruses from docking to / entering host cells
- neutralisation of toxins- bind to the toxins produced by pathogens, preventing them from affecting susceptible cells
- activation of complement- antibodies activate a complement cascade which leads to the formation of a membrane attack complex that forms a pore in the membrane of the pathogen allowing water and ions to enter the cell and causing lysis
- agglutination of pathogens, preventing cell entry and aiding ingestion by pathogens
what is the complement system?
a collection of proteins which ultimately lead to the perforation of the membranes of pathogens
what does immunity depend upon?
the persistence of memory cells
describe how vaccines lead to immunity
they contain antigens that trigger immunity by causing a primary immune response but do not cause the disease
if the actual pathogen enters the body, it will be destroyed by the antibodies in a secondary immune response
what was the first infectious disease of humans to have been eradicated by vaccination?
smallpox
give 3 reasons why the smallpox eradication campaign was successful
- only humans can catch and transmit smallpox. there is no reservoir where the disease could be maintained and re-emerged
- symptoms of infection emerge quickly and are readily visible allowing teams to ‘ring vaccinate’ all of the people who might have come into contact with the afflicted person
- immunity is long-lasting
pathogens can either be
species-specific or able to cross species barriers
define a zoonosis
a pathogen which can cross a species barrier
these are a growing health concern
when and how are histamines released?
- by mast cells (immune cells found in connective tissue) secrete histamine in response to infection
- by basophils which circulate in the blood
state the effect of histamine on blood vessels
causes the dilation of the small blood vessels in the infected area causing the vessels to become leaky. This increases the flow of fluid containing immune components to the infected area and allows for some of the immune components to leave the blood vessel resulting in both specific and non-specific responses.
Sensitization: Initial exposure to allergen and
Allergic Reaction: Secondary exposure to same allergen
- when a specific B cell first encounters the allergen, it differentiates into plasma cells and makes large quantities of antibody (IgE)
- the IgE antibodies attach to mast cells, effectively ‘priming’ them towards the allergen
- upon re-exposure to the allergen, the IgE-primed mast cells release large amounts of histamine which causes inflammation
symptoms of an allergic reaction
nose: itching, fluid build-up, sneezing, mucus secretion and inflammation
allergic rashes and dangerous swelling (anaphylaxis)
define monoclonal antibodies
highly specific, purified antibodies that are produced by a clone of cells derived from a single cell. they recognise only one antigen
what is the use of monoclonal antibodies?
the treatment and diagnosis of diseases; eg the test for malaria or the creation of antibodies for injection into rabies victims
define a hybridoma cell
the cells formed by fusion of antibody-producing plasma B cells and myeloma (tumour) cells, which produce monoclonal antibodies
describe how hybridoma cells are created
- antigen recognised by the antibody is injected into a mouse or other mammal
- the mouse’s immune system makes plasma B cells that are capable of producing the desired antibody
- plasma cells are removed from the spleen of the mouse and fused with cancer cells called myeloma cells
describe how pregnancy tests work with a diagram
kits use monoclonal antibodies to detect hCG, which is produced during pregnancy by the developing embryo and the placenta. the urine of pregnant women contains detectable levels of hCG
- free monoclonal antibodies specific to hCG are conjugated to an enzyme that changes the colour of a dye
- a second set of monoclonal antibodies specific to hCG are immobilised to the dye substrate
- if hCG is present in urine, it will interact with both sets of monoclonal antibody (forming an antibody ‘sandwich’)
- when both sets of antibody are bound to hCG, the enzyme is brought into physical proximity with the dye, changing its colour
- a third set of monoclonal antibodies will bind any unattached enzyme-linked antibodies, functioning as a control
