6.3 defence against infectious diseases Flashcards
skin and mucous membranes are _____ and serve as the _____ line of defence
surface barriers, first
how does skin serve as primary defence against disease-causing pathogens? (4)
- protects external structures
- epidermis is made out of dead skin cells -> form an impermeable layer
- sebaceous glands secrete chemicals and enzymes -> inhibit microbial growth
- secrets lactic acid and fatty acids -> lower pH
how do mucuous membranes serve as primary defence against disease-causing pathogens? (4)
- protects internal structures e.g. trachea, oesophagus
- consists of a thin region of living cells -> release fluids to wash away pathogens
- secretes lysozomes -> destroy cell walls of pathogens
- epithelial cells secrete mucous -> traps pathogens -> mucous containing pathogens are swept away for disposal by cilia
how does blood clotting protect the body?
- prevents blood loss
- prevents entry of pathogens into the bloodstream
outline how blood clots are formed when there is a cut (5)
- coagulation cascade occurs -> stimulated by clotting factors released by damaged cells and platelets
- clotting factors cause platelets to become sticky -> adhere to damaged region -> form a solid plug
- clotting factors trigger the conversion of prothrombin -> thrombin
- thrombin catalyses the conversion of soluble fibrinogen -> insoluble fibrin
- fibrin strands form a mesh around platelet plug -> traps blood cells -> form a temporary clot
what is the formation of a blood clot in the coronary arteries?
coronary thrombosis
how do blood clots form in coronary arteries? (7)
- when vessels are damaged -> cholesterol deposited
- atheromas develop in arteries which can calcify over time -> reducing the diameter of the lumen
- restricted blood flow -> incr. pressure -> damage of arterial wall
- damaged region is repaired w fibrous tissue -> significantly reduces elasticity of vessel wall
- smooth lining progressively degraded -> atherosclerotic plaques form
- if plaque ruptures -> blood clotting triggered, forming a thrombus -> restricts blood flow
- if the thrombus is dislodged it can cause blockage in smaller arterioles
why are blood clots dangerous?
occlusion of a coronary artery by a blood clot may cause a heart attack
what are the two key properties of the innate immune system?
- non-specific
- non-adaptive
how do phagocytes give rise to non-specific immunity? (6)
- phagocytic leukocytes move into body tissue in response to infection
- damaged tissues release chemicals -> draw white blood cells to the site of infection
- pathogens are engulfed by pseudopodia which surrounds the pathogen and then fuses -> forms an internal vesicle
- lysosome fuses with vesicle -> pathogen digested
- antigens presented on the surface of phagocyte -> stimulate third line of defence
what are two characteristics of the adaptive immune system?
- specific, targets a response specific to pathogen
- immunological memory, responds rapidly to re-exposure of pathogen
how are antibodies produced? (4)
- when phagocytic leukocytes engulf a pathogen -> some present antigens on e surface (dendritic cell)
- these cells migrate to the lymph node -> activate specific helper T lymphocytes
- helper T cells release cytokines, activating particular B cell to be capable of producing antibodies specific to antigen
- activated B cell divides and differentiates -> form plasma cells -> produce high amounts of antibodies
how do B cells contribute to long lasting immunity?
a small proportion of activated B cell will develop into memory cells
what are antigens? (short defin.)
a substance that the body recognises as foreign and that will elicit an immune response
what are antibodies? (short defin.)
a protein produced by B lymphocytes that is specific to a given antigen
what do antibodies do to help the immune system? (5)
- target specific antigen on pathogen -> enhances capacity of immune system to recognise + destroy pathogen
- neutralises pathogens -> bind to antigens present on pathogens -> prevent them from infecting host cells
- one antibody can bind to two pathogens -> large scale agglutination can occur
- precipitates dissolved antigens like toxins + foreign molecules
- activate the complement system -> increases rate of phagocytosis of the pathogens
how do antibiotics function? (short ans)
they kill or inhibit the growth of microbes by targeting prokaryotic metabolism
why are antibiotics ineffective in killing viruses? (short ans)
viruses do not possess metabolism and instead take over the machinery of infected host cells
name 2 cell parts antibiotics target
- components of cell walls
- 70s ribosomes
how does penicillin function as an antibiotic? (2)
- are competitive inhibitors of an enzyme needed to form the cell walls of many types of bacteria
- cell walls are needed to maintain structural stability of the cell membrane -> damage to cell membrane -> bacteria death
how does streptomycin function as an antibiotic? (3)
- binds to 16s rRNA found in 70s ribosomes in prokaryotes
- binding to ribosomes interfere w binding of tRNA to ribosomes -> resulting in errors in e translation process in protein synthesis
- affects entire metabolic process -> death of bacteria
why are some bacteria resistant to antibiotics? (4)
- bacteria may evolve with genes that confer resistance to antibiotics
- eg. beta lactamase gene -> produces beta lactamase which breaks down beta lactam group of antibiotics
- resistant strains of bacteria proliferate very quickly after initial mutation
- resistant strains can pass resistance genes to susceptible strains by bacterial conjugation
why are there increasing antibiotic-resistant bacterial strains? (2)
over-prescription, misuse
how was penicillin discovered? (short ans)
- a plate containing S. aureus was contaiminated with penicillium mold culture
- a halo was found around the mold -> showing that bacterial were killed by the extracellular secretions of the mold
how did the florey and chain experiment show that penicillin can be medically applied?
- florey tested penicillin on infected mice
- eight were injected with streptococcus bacteria
- four were injected with penicillin
- untreated mice died of bacterial infection while the treated mice survived
- demonstrated antibiotic potential as it killed bacterial and not human cells
what are the effects of HIV? (5)
- HIV specifically targets the helper T lymphocytes which regulate the adaptive immune system
- following infection, virus undergoes a period of latency -> allows infected T lym to reproduce
- virus becomes active + begins to spread -> destroying T lym
- depletion of functional T lym -> antibodies cannot be produced -> immune system is weakened -> cannot effectively mount immune response against opportunistic infections
- body becomes susceptible to opportunistic infections -> death if body cannot defend itself
how is HIV transmitted? (short ans)
- unprotected sex
- blood transfusion
