6.3 Defence against infectious diseases Flashcards
how does the skin act as a barrier to infection
the skin and mucous membrane from a primary defence against pathogens that cause infectious disease
microbes commonly live outside the human body but some are specialised inside the human body
the outer most layer of the skin is tough and a barrier as well as being a protection against chemical and physical damage
sebaceous glands which are assosciated with hair follicles secrete sebum, a chemical which maintains skin moisture adn slightly lowers the pH of skin inhibiting the growth of bacteria and fungi
mucous membranes are thinner and softer types of skin found in e.g. the nasal passage and airway and vagina
the mucus is a sticky solution of glycoproteins which acts a physical barrier and traps harmful particles to be swallowed or expelled- also has antiseptic properties due to the presence of teh anti- bacterial enzyme lysozyme
e..g in the airway the cilia will waft the mucus (released by goblet cells) to the airway where it is swalled and teh acidic stomach breaks it down
how are cuts sealed
clotting - needs to be strictly controlled as can lead to blockages in blood vessels
the blood changes from a liquid to a semi-solid this seals the wound and prevents loss of blood and blood pressure and prevents entry of pathogens
blood clotting involves many reactions each of which produces a catalyst for the next reaction.
platelets release clotting factors, platelets aggragate at the site of a clot, the cascade of reactions caused by clotting factors cause teh enzyme thrombin to be produced which converts teh soluble protein fibrinogen into the insoluble one fibrin whic h forms a mesh that traps more platelets and blood cells
blood clot - thrombus
what are the causes and consequences of coronary thrombosis
blood clots form in the coronary arteries which branch off from the aorta close to the semilunar valve - carry nutrients to cardiac muscles
if it becomes blocked by a clot part of the heart is deprieved of oxygen and nutrients so not enough atp is produced by aerobic respiration. Contractions become irregular and uncoordinated.
—> heart makes fibrillations (quivering movements) and blood is not effectively pumped –> can be fatal
atherosclerosis can cause occulsion in coronary arteries. where atheromas developes in the endothelium, the endothelium becomes damaged and roughened, especially the artery wall is hardened by deposition of calcium salts
- this increase the risk of coronoary thrombosis
increase risk of cornary thrombosis
- coronary occlusion
- damage to the capillary epithelium
- hardening of arteries
- rupture of athermoa
- smoking
- high blood cholesterol
- diabetes
- obesity
- lack of exercise
what do phagocytes do
ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to diseases
they squeeze out through pores in teh walls of capillaries and move to the site of infection
they then engulf pathogens by endocytosis and digest tehm with enzymes in the lysosomes
when there is a big wound many pathogens are attracted so pus is formed
how and why are antibodies produced?
production of antibodies by lymphocytes in response to particular pathogens gives specific immunity
any chemical that stimulates a specific immunity response is an antigen - antibodies bind to the antigen which is on the pathogen
antibodies are each produced by one type of lymphocytes
we therefore are forced to have small numbers of lymphocyte for each disease to make sure we have enough types of antibodies covered BUT antigens on the pathogen stimulate cell division of the specific lymphocyte required
a large clone of the lymphocyte called plasma cells are produced within a few days and these secrete large enough quantities of teh antibody to control the pathogen and clear the infection
what are antibodies? what do they do
large proteins that have two functional regions - a hypervariable region that binds to a specific antigen adn another region that helps the body to fight the pathogen by
- making a pathogen more recognisable to phagocyte
- preventing viruses from docking to host cells so they cannot enter teh cells
what and why are memory cells
antibodies are only present for a a few weeks/months and the plasma cells are gradually lost after the infection is overcome
but some of the lymphocytes produced during the infection are not active plasma cells but become memory cells - long lived
they remain inactive unless the same pathogens reenters the body when they become active and divide to produce plasma cells faster, sooner and in greater quantity
effects of HIV on the immune system and methods of transmission
the production of antibodies includes the helper T-cells which teh HIV virus destroys - loss of capacity to produce antibodies progressively
in early stages teh immune system makes antibodies against HIV - HIV postive blood has these
HIV is a retrovirus - genes made of RNA and uses reverse transciptase to make DNA copies of its genes when it enters a host cells – can use antiretroviral drugs
HIV postive patients eventually are attacked by oppertunistic pathogens which cannot be fought off by the weakened bacteria
a collection of diseases existing together are called a syndrome so when teh syndrome of diseases due to HIV is present you are said to have aquired immune deficiency syndrome (AIDS)
spread by
- sexual intercourse during whichj abrasion to the mucous membrane of the penis in the vagina can cause minor bleeding
- transfusion of infected blood or blood products such as Factor 8
- sharing of hypodermic needles by intravenous drug users
4.
how do antibiotics work and how were they discovered
block processes that occur in prokaryotic cells but not eukaryotic cells
inhibits teh growth of microorganisms
target bacterial dna replication, transcription, translation, ribosome function, cell wall formation
many antibacterial antibiotics were discovered in saphotrophic fungi which compete with saphotrophic bacteria for the dead organic matter on which they both feed by secreting antibacterial antibiotics to inhibt the growth of their competitors
it is produced by some strains of the penicillium fungus but only when nutrients are scare and competition is harmful
who tested penicillin and how
florey and chain tested penicillin on bacterial infections on mice
florey and chain investigated teh use of chemical substance to control bacterial infections so they took alexander felmings work in 1928 = penicilin
- method for growing fungus penicillium in a lquid culture that stimulates it to secrete pencillin
- methods for producing reasonably pure penicilin
worked on agar plates but needed to test on humans, first mice, 8 mice deliberately infected with steptococcus to casue pneumonia, 4 given penicillin which survived
chose 43 year old who had an accute life threatening bacterial infection, was given penicillin for 4 days, improved, them relapsed due to lack of enough penicillin and died
larger quantites produced and 5 more patients tested all cured of infections.
pharmaceutical companies then began producing penicllin in larger quantites so allow for extensive testing
examples of drugs that caused problems
thalidomide - found to relieve mornings sickness, had not considered side effects on fetus and over 10 000 babies born with birth deformities
TGN1412 given to 6 volunteers, supposedly to treat autoimmune diesaes and leukemia, led to multiple organ failure, recovered by may be long term consequence
how do viruses and antibiotics relate
viruses do not have a metabolism so can be treated using antibiotics
they use the chemical processes of a host cell instead so cannot target these processes as teh host cell would be damaged
use of antibiotics in infective and contributes to the antibiotic resistance
antiviral drugs target viruses but these are few and far between
describe causes and consequences of antibiotic resistance
some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains of bacteria have multiple resistance
if a bacteria is resistance to one antibiotic not a problem but multiple resistance e.g. staphylococcus aureus is - more than 300 000 cases world wide
- doctors prescribe only if serious
- patients complete course of antibiotics
- hospital staff maintain high level of hygiene to eliminate infections spreading
- farmers not using antibiotics in animal feed
- pharamceutical companies creating new antibiotics
