Unit 4 Mrs Goodall

8/8/2019 Unit 4 Mrs Goodall

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Unit 4

Topic 6 Forensic Science

Determining the time of death

y Not an easy task, especially if the body has been dead for over 48 hoursy Forensic scientists look for the changes that take place in the body after deathy These include:

o Body temperature dropso Muscles contract and they become rigid (Rigamortis)o The body tissues decay

Drop in body temperature

y Why does the body temperature drop after death?o Metabolic reactions stopo Heat energy is transferred from the surface of the body by radiation,

conduction and water evaporation

o The body temperature starts to fall straight after death but plateaus for awhile before falling gradually to room temperature

y Factors affecting the rate of coolingo Mode of death bleeding causes the drop to be much sharpero Clothingo Size of the body and the level of fato Environment

Muscle contraction

y When a person dies the muscle cells (Unlike other tissues like the brain) do notimmediately die

y This is because the have large stores of ATP and glycogen and can continue to respireanaerobically for a time

y As the muscle cells run out of ATP, the muscle fibres become permanentlycontracted

y Rigor mortis starts about 2-4 hours after death and needs between 6 and 8 hours totake full effect

y It begins in the muscles of the face and neck and then progresses down the bodyo What can affect how quickly rigor mortis sets in?o The amount of ATP stored in the muscles at the time of death


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o Different people have different levels of ATP depending on their genetics andtheir level of fitness

o The levle of ATP also depends on the level of activity before death E.g Rigor mortis usually sets in very quickly in drowning victims,

because they have used up all their muscle ATP struggling to stay

afloat

o The temperature of the person when they die and the temperature of thesurroundings also affect how quickly rogor mortis se ts in

y Rigor mortis is not permanent it usually passes between 36 and 48 hours afterdeath

y This is because enzymes released from the lysosomes break down the muscle tissueand so soften it

y Working backwards, it is possible to estimate the time of death by calculating whenthe ATP store was full

The state of decay

y As cells die the digestive enzymes start to break down the walls of the gut and thesurrounding cells.

y Lysosomes within the cells rupture and release enzymes which break down the cells.y The body is now an ideal habitat for decomposers.

Stages of succession in decay

Colonisers

y The first colonisers will be the anaerobic bacteria which are usually found in the gutbut now thrive in the lactic acid rich environment of the muscles after death

y As enzymes break down cells, the bacteria spready The next colonisers are flies

o Blowflies are extremely sensitive to the smell of dead organisms and canappear on a body within minutes of death

o The flies lay eggs in the dead body

o The maggots hatch and immediately being feeding on the tissues breakingthem down

o The maggots burrow deep into the flesh, eventually pupate, turn into flies anfthen mate and the whole cycle starts over again

o As the soft tissues of the body liquefy, flies can feed on this tooy Next come the beetles that will lay their eggs on the body so that their larvae can

feed on the fly maggots


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y Then parasytic wasps appear to lay their eggs in the fly and beetle larvaey Different species such as cheese flies and coffin flies appear on the bod yy As the body is digested it dries outy Eventually the body is too dry for the maggots and a number of beetle species with

strong mouthparts arrives which feed on the remains of the muscles and the

connective tissues

y These include:o Carcass beetles, ham beetles and hide bettles.

y At the very end, mites and moth larvae will feed on the hair until only dry bones areleft.

Why would a buried body decay more slowly than a body left in the open air?

y It is less available to decomposersy The temperature is lowery The warmer the body, the faster rate of decay as all the chemical reactions are

speeded up

y The greater the level of exposure to decomposers, the faster the rate of decay.Forensic Entomology

y This is the study of insect life as it relates to crimey The first recorded case of forensci entomolgy being used to solve a murder in the UK

was in 1935

y When a body is discovered, eggs, maggots and pupae are collected.They are grownto adults to aid thier identification and this evidence is used to help estimate howlong a body has been in the place it is found

y Each species has a different length life cycle which makes calculating the time ofdeath even more accurate.

y E.G.If a body found outside had no evidence of blowfly activity, the forensicscientists would know that the body had almost certainly been there for no more

than 24 hours.

Questions Pg 67 Q1-3

1. 1a. The body of a mammal cools after death because all metabolic

reactions in the body stop

b. The cooling rate is slower in the first hours after death because themuscles are still using up their reserves of ATP so there are still

reactions going on causing heat to be given off still.

c. External temperature will affect the rate of cooling as bodytemperature changes through conduction and radiation so if the


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temperature outside is cold, it will be transfered through the body.

Also if the body is outside but covered up, the rate of cooling will take

longer as the heat will radiate slower.

2. The temperature of a lizard or frog would not go down as they are coldblooded and so there is no need for the temperature to drop.

3. Rigor mortis is of limited used in determining the time of death because itonly lasts a few days at the most and after that the body l oosens.

Questions Pg 71,Q1-4

1. The first colonisers will be the anaerobic bacteria which are usually found inthe gut but now thrive in the lactic acid rich environment of the muscles after

death. As enzymes break down cells, the bacteria spread.The next colonisers

are flies.Blowflies are extremely sensitive to the smell of dead organisms and

can appear on a body within minutes of death The flies lay eggs in the dead

body The maggots hatch and immediately being feeding on the tissues

breaking them down The maggots burrow deep into the flesh, eventually

pupate, turn into flies anf then mate and the whole cycle starts over again As

the soft tissues of the body liquefy, flies can feed on this too Next come the

beetles that will lay their eggs on the body so that their larvae can feed on

the fly maggots Then parasytic wasps appear to lay their eggs in the fly and

beetle larvae Different species such as cheese flies and coffin flies appear on

the body As the body is digested it dries out Eventually the body is too dry for

the maggots and a number of beetle species with strong mouthparts arrives

which feed on the remains of the muscles and the connective tissuesThese

include:Carcass beetles, ham beetles and hide bettles.At the very end, mites

and moth larvae will feed on the hair until only dry bones are left.

2. Temperature affects decomposition rate as a warmer body experiences fastchemical reactions increasing the decay speed.Exposure also affects

decomposition rate as a more exposed body is more available to

decomposers than a covered body.

3. The process of succesion is helpful to forensic scienctists to determine thetime of death as each bug has a different life cycle and each bug occurs at a

different time period of decay helping to pin point an exact time of death. 4. Question 4

a. In the first few days after death, all 3 of the temperatures dropsignificantly.The bodies temperatures drop rapidly because there

are no longer any chemical reactions producing energy happening in

the body and so will not be able to maintain warmth. Also the air

temperature has dropped which will lead to a faster rate of decline.


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The temperature of the buried body never drops below 10 degrees

centigrade and never rises above 17 degreesC after 5 days.I believe

this is because the body is insulated by the soil and so the fluctuating

temperature above ground will not affect it as much.The exposed

body temperature, however, changes much more because it is in the

open air.So at night, the body will be cooled down by the colder

temperatures and winds wheras during the day, the sun will warm it

up.

b. The advantages of using pigs is that it is a lot more ethical than usinghumans.Plus the pigs are mammals, meaning they will decompose in

a similar way to humans.The disadvantage of using them is that pigs

are of course very different to humans in their physical appearance

and weight etc.So any results in experim ents should be used as just

rough guidelines instead of any solid measurements.

c. The advantages of using humans is that the results will be far moreaccurate and will therefore be a lot more useful.However despite the

very large up-side, the problem with using humans is that it is

frowned upon and is very unethical.

Protein synthesis notes continued from paper copy in folder.

y Triplet codeo Three nucleotide bases (A codon) codes for one specific amino acid

y The code is degenerateo A given amino acid may be coded for by more than one codon

y It is non-overlappingo Each base is only part of one codon, and each codon codes for one amino

acid

y It is almost universalo The same sequences of bases code for the same amino acids in all organisms

Transcription

y STAGE 1o Firstly the enzyme helicase splits the hydrogen bonds between the bases in a

specific region of double stranded DNA in the nucleus.This causes the tw

strands to separate

y STAGE 2o RNA polymerase binds to a base sequence called the promoter region.This

determines which way the RNA polymerase faces and hence which region is

used as a template


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y DNA contains some regions that do not code for proteins.There a re known asintrons

y To produce functional proteins these introns need to be spliced out of the mrna,leaving only the regions that code for proteins called exons

y A molecule called a spliceosome removes the introns, producing mature mrna thatcontains only exons.Before splicing, mrna is known as pre-mrna

Post translational modifications

There are several ways in which the protein from the original gene may be modified

y The start codon methionine is often removed by enzymesy Functional groups may be addedy There may be structural changes to the polypeptide chain

DNA Profiling

Why might DNA be analysed?

y Crimes/ Evidencey Paternity testingy Genetic screening Cystic fibrosis in foetus y Linking animals/plants Evolutionary linksy Identification of a body Mutilation after natural disasters.

Often the quantity ofDNA obtained is not enough for analysis, so it must be multiplied

This is achieved with the polymerase chain reaction.

What does the PCR reaction mixture contain

y The sample ofDNAy An excess of two primersy DNA polymerasey Nucleotides

The target length ofDNA to be copied is selected using primers.

Primer = a single stranded length of 20 to 30 nucleotides which are artificially synthesised.

Its sequence complements the sequence at the end of the targetDNA.

2 Primers are used, 1 complementary to each strand.


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Process

y The mixture is heated to 95o C to separate the DNA strands (Breaking H bonds)y The mixture is colled to 55oC to allow the primers to join to their strandsy The mixture is then heated to 72C to allow fresh DNA strands to be synthesisedy The mixture is further heated to separate these strandsy The cycle take 2 minutes and is repeated

DNA Profiling

y Introns are the regions of the chromosomes which are used inDNA profilingy Within the introns there are micro -satellites and mini-satellitesy Mini-satellites = 20-50 base sequence repeated from 50 to several hundred timesy Micro-satellites = 2-4 bases repeated between 5 and 15 timesy The number of repeats of each satellite will vary between individuals as different

patterns may be inheritedy There are many different introns and a huge variation in the number of repeats so

the liklihood of any 2 individuals having the same pattern of DNA is extremely

remote, unless they are identical twins

y The more closely related 2 individuals are, the more similar are theirDNA patternsPreparing the DNA

y Strands ofDNA from a sample are chopped up into fragments using enzymes calledrestricted endonucleases

y These enzymes cut the DNA at particular points in the intron sequences called therecognition sites

y Using restriction enzymes that cut either side of mini and micro satellite units leavesthe repeated sequences intact, giving a mixture ofDNA fragments made up largely of

mini and micro satellite sequences

Gel Electrophoresis

y The DNA fragments are placed in wells in an agarose gel medium in a bufferingsolution (To maintain a constant PH), with known DNA fragments to aid

identification

y The gel contains a dye (E.g. ethidium bromide) which binds to the DNA fragments inthe gel.The dye will fluoresce when p laced under UV light .

y A dye is also added to the DNA samples.This moves through the gel slightly fasterthan the DNA so that the current can be turned off before all the samples run off the

end.


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y An electric current is passed through the gel and the DNA fragments move towardsthe positive anode because od the negative charge on the phosphate groups in the

DNA

y The fragments move at different rates depending on the their massy Once the electrophoresis is completem the plate is placed under UV light.The DNA

fluoresces and shows up clearly so it can be identified

y This method shows up large DNA fragments, containing a minimum of 50 base pairs( mini-satellites)

Southern blotting

y To identify specific sequences, southern blotting can be used.y An alkaline buffer solution is added to the gel after elctrophoresisy This separates the DNA strands so that the base sequences are exposed.y A nylon filter or nitrocellulose paper is placed over the gel and theD NA is transferred

to the filter.y Gene probes can then be used to identify specific base sequences on the filter.

Gene probes

y Gene probes are short DNA sequences that are complementary to the specificsequences whice are being sought

y The probe is labeleld either radioactively or with a fluorescent moleculey Large amounts of the gene probes are added to the filter and bind with

complementary DNA strands.They can then be identified by X-Ray or under UV light

y Gene probes are used for picking out micro satellites regions (

Short tandem repeats)

Which are now widely used in DNA identification

y Statistically the chances of 2 people matching on 1 or more of these sites is so smallthat it is counted as reliable evidence in court


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o Small pox viruso Adenoviruso Bacteriophage (Viruses that infect bacteria)

y RNA viruses contain RNA which uses the enzyme reverse transcriptase to makeDNAmolecules

y The DNA is used as a template for new viral proteins and ultimately a new RNAgenome

y Examples of RNA viruses:o HIVo Tobacco Mosaic Virus

Virus life cycles

y Viruses reproduce only within the cells of the bodyy They attack their host cells in several different ways:7y E.g.Bacteriophages inject their genome into the host bacterial cell but the bulk of

the viral material remains on the outside of the bacterium

y Viruses that infect animal cells have diffrent methods of entering the cello Endocytosis With or without the envelope and the host cell digests the

capsid releasing the viral genetic material

o The envelope fuses with the host cell surface releasing the rest of the virusinside the membrane

y Plant viruses get into plant cells typically using a vector (an insect) to pierce thecellulose cell wall.

Lysogenic pathway

y Many viruses are non virulent when they first enter the host celly They insert their DNA inot the host DNA so it is replicated every time the host cell

divides.This inserted DNA is called a provirus

y Mrna is not produced from the viral DNA because the viral genes cause theproduction of a repressor protein which makes it impossible to transcribe the rest of

the genetic material

y This period is called lysogeny.The virus is part of the reproducing host ce lls but isdormant

Lytic Pathway

y Under certain conditions e.g. when the host cell is damaged, viruses in the lysogenicstate are activated


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y The amount of repressor protein decreases and the viruses enterthe lytic pathwayand become virulent.

y The viral genetic material is replicated independantly of the hostDNA after enteringthe host cell

y Mature viruses are made and the host cell bursts releasing large numbers of the newvirus particles to invade other cells

y The virus is virulentRetrovirus life cycles

y Retroviruses e.g.HIV have a more complex life cycley Their genetic material is viral RNAy This can not be used as Mrna.It is translated into DNA by reverse trnascriptase in the

cytoplasm of the cell.

y The viral DNA passes into the nucleus of the host cell where it is Inserted into thehost DNA

y Host transcriptase enzymes make viral mrna and the new viral particles leave the cellby exocytosis

y The host cell functions as a virus making factory whilst the new viruses move on toinfect more cells.

Viruses and disease

y Viruses cause disease in animals, plants and bacteriay They cause the symptoms of disease by:

o The lysis of the host cell

o Causing the host cell to release their own lysosomes and digest themselvesfrom the inside out

o Production of toxins that inhibit cell metabolism y Viral infections are often specific to particular tissuesy E.g. adenovirus which causes colds, affects the respiratory tract but does not cause

damage to brain cells

y The specificity is caused by cell markers on the surface of host cells.Each type of cellhas its own recognition markers and different viruses can only bind to particular

markers

y The presence or absence of these markers can make groups of organisms vulnerableto attack by viruses.

BACTERIA!

y Bacteria are prokaryotic organisms and the most common form of life on earth.y Some bacteria are pathogens but the majority are not harmful and may even be

beneficial to living organisms.


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The structure of bacteria

y All bacteria have a cell wally The contents of bacterial cells are usually hypertonic to the medium around them.

This means that water moves into the cells by osmosis

y The cell wall prevents the cell from bursting, maintians the shape, gives support andprotection

y The cell surface membrane is similar in structure and function to eukaryotic cellsy Bacteria have no mitochondriay The respiratory enzymes are located on the cell membrane.y In some bacteria the cell membrane shows infoldings called mesosomes.The

function of these is still debated.

y Some have a capsule around their cells walls.This may be formed by starch, gelatin,protein or glycolipid.

y It protects the bacteria from phagocy tosis by white blood cells. y The capsule also covers the cell markers on the cell membrane which identify the cell.

This make it easier for the bacterium to be pathogenic as it is not identified by the

hosts immune system.

y The capsule is also presentto help it survive dry

conditions.

y Some bacteria have one toseveral hundred thead like

protein projections called

pili (Or fimbriae)y They are used for

attachment to a host cell

and sexual reproduction.

y They can make bacteriaprone to viral infection as

bacteriophages can use the pili as an entry point to the cell.

y Some bacteria can move themselves by flagella.Thye are made from a a manystranded helix of the platein flagellin.

y The genetic material is a single length of circular DNA free in the cytoplasm y Some bacteria conatain plasmids which code for a particular bacterial phenotype e.g.

production of toxins


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Bacterial Cell Walls

y The bacterial cell wall consists of a layer of peptidoglycano Peptidoglycan is made up of many parallel polysaccharide chains with short

peptide cross linkages, creating a large net like structure

o There are two types of cell wall that are identified by gram stainingo Before the bacteria are stained they are colourless

y Gram positive bacterao The cell walls of gram-positive bacteria e.g.MRSA have a thick layer of

peptidoglycan

o The peptidoglycan contains chemicals such as teichnoic acid within their netlike structure

o The crystal violet in the stains bind to the teichoic acid and resistsdecolouring in the rest of the process, leaving the positive blue/purple colour

y Gram negative bacteriao The cell walls of gram negative bacteria have a thinner layer of peptidoglycan

with no teichoic acid between the membrane layers

o The outher membrane like layer is made up of lipopolysaccharides. o Any crystal violet which does not bind is readily de colourised and replaced

with red safranine in the gram stain, so the cells appear red.

Classifying Bacteria

y Bacteria can be classified according to shape:o Sphericalo Rod shapedo Twistedo Comma Shaped

y They can also be grouped by respiratory requirmentso Obligate aerobes need oxygen for respirationo Faculative anerobes use oxygen if available but can cope without (Most

pathogens)

o Obligate anaerobes can only respire without oxygenBacteria Reproduction

y Bacteria can reproduce in two main ways, the most common is asexual reproductionby binary fission

y When the bacteria reaches a certain size, enzymes break open the circularDNAletting the strands unwind and replicate

y New cross walls are laid down between the two new daughter cells.Mesosomesappear to play a role in this .


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y New cell membrane and cell wall material extends inwards, creating a septum whichdivide the daughter cells in two, each containing a circular chromosome attached to

the cell membrane

y Plasmids divide at the same time and asre often present in the daughter cellsy The time between cell divisions is called the generation time.y Bacteria can reproduce in an alternative way to asexual reproduction by thew

transfer of genes between bacteria (not always of the same species)

y There are three ways genetic material can be passed from one bacterium;o TRANSFORMATION A short piece ofDNA is released by a donor and

actively taken up by a recipient where it replaces a similar piece ofDNA

o TRANSDUCTION A small amount ofDNA is transferred from 1 bacterium toanother by a bacteriophage.They are incorporated into the host DNA

o CONJUGATION Genetic material is transferred by direct contact.The donorcell is analogous to a male cell and produces a sex pilus (a cytoplasmic bridge)

between the 2 cells through whichD

NA is transferred to the recipient cell.

The male cell contains the fertility factor which is a plasmid that codes for the

sex pilus

Questions page 89

1. Bacteria usually use asexual reproduction because it only requires one cell, andso is therefore safer and more convenient.It is also very quick and reliable

2. Bacteria sometimes use a form of sexual reproduction because it allows genesto be transferred into another cell and so therefore add to the genepool of the

bacteria.This also makes it harder for use to fight against bacterial disease.

3. It shows that genetic material can be taken up by bacteria in sufficient quantity4. When the dead bacteria werwe attacked by enzymes that destroyed

carbohydrates and proteints it had no effect on FFSI NEEDTHE ANSWERS

Bacteria as Decomposers

Bacteria in the carbon cycle

y Organic compunds pasas to the decomposers when producers die, excrete,decompose.

Infection by pathogens

How do bacteria make people unwell?

y Endotoxins


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o Lipopolysaccharides which are part of the outer layer of gram-negativebacteria

o Rarely fatal, cause symptoms usch as diarrhoea, fever, vomiting eg.g E-coli,salmonella.

y Exotoxinso Soluble proteins produced as the bacter ia metabolise and reproduceo Many different types that have differrent effects e.g. damage cell

membranes, inhibitors, poison cells

o Most dangerous and fatal bacteria diseases .Spreading disease

Ways in which disease is spread

y Airborne Inhalationo Coughing and sneezing and talking expel droplets that can contain pathogens

if you have an infection

o Part of the water in the droplets evaporates leaving tiny droplets containingthe pathogen which remain suspended in the air

o When the droplets gain entrnace to a new respiratory tract they can initiatean infection. E.g.Flu, TB, Measles

y Toucho Very common in spreading disease in children and sexual disease.E.g.

Impertigo

y Food Ingestiono Transmitted through contaminated foodo Greatest risk through raw and uncooked foodo Only a small quantity required to cause diseaseo E.g.Most forms of diarrhoea, hepatitis

y Vectorso A living organism that transmits infection from one host to another.Many

insects are vectors.E.g.Malaria

y Inanimate objects Fomiteso These are objects that carry pathogens from one host to another.E.g.

hospital towels, make up.E.g.MRSA

y Inoculationo Pathogen enters through a break in the skino Transmission maybe through contaminated surgical equipment or shared

needles.

o E.g.HIV, Rabies, Hepatitis


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Natural Defences

y The body has several non-specific defences1. Epithelial defences (Skin)

A physical barrier toughened by keratin. Produces sebum which contains chemical that inhibit the growth ofmicroorganisms. Natural skin flora prevents disease by competing for position on the

skin and produces chemicals that inhibit the growth of

microorganisms

Natural skin flora is not affected by sebum (but can be affected bywashing too often with antibacterial soap)

Surfaces of the internal tubes and ducts are more vulnerable as theyare thin and not toughened by keratin.

Cilia carry mucas, germs and dust particles up to the gullet where theyare swallowed and pass out of the body in the faeces.

The mucas contains lysozymes (Also found in tears) Lysozymes (Enzymes able to destroy bacterial cell walls) are very

effective against gram positive bacteria.

They break down the cross linkages in the peptidoglycans in the cellwall.

Phagocytic white cells are found on the epitithelial surfaces. If the skin is cut, pathogens can then enter the bloodstream directly. Some biting insects can penetrate the skin themselves. The bodies first response to a break in the skin is to seal the wound

through a clotting mechanism.

The digestive system helps to defend the body against pathogensbecause some polypeptides produced in the salivary glads destroy

bacteria and others slow down growth.The hydrochloric acid in the

stomach destroys the majority of bacteria ingested.The gut flora also

competes successfully for nutrients and produces anti -micorbial

compunds.The stomach helps protect against disease and illness by

vomiting.It can be cuased by toxins, bad smells, tumours, pregnancy

and infection of the gut.


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Non-Specific Responses to Infection

y When pathogens enter the body the are recognised and destroyed or inactivated.y This response is a results of a number of different systmes in he body that depend on

cell recognition.

Cell Recognition

y On the outer surface of the cell memb rave are many proteins eg.Glycoproteins.y These can be varied and appear to p[lay a role in cell recognition and possibly in cell

adhesion.

y They act as antigens.o An antigen is a substance that stimulates the production of an antibody when

pathogens enter the body (Specific immune responce)

y The body should only produce antiboddies in response to non self antigens.Inflammation

y Common non-specific way the body responds to infectiony Occurs when infection is localised E.g. when bacteria colonises a cut.y Mast cells (Specialised cells in the connective tissue below the skin) and white blood

cells release histamines

y Histamines cause the blood vessels in the local area to dilate causing heat andredness

y The raised temperature reduces the effectiveness of pathogen reproduction.y The dilation makes the capilliary cells leaky.y The fluid including plasma, wbc and antibodies is forced ou t of the capilliaries

causeing oedema and pain.

y The WBC and antibodies disable and destroy the pathogen.y A common symptom of widespread infection is a rash, which is inflammation or

tissue damage that particularly affects the skin, causin red spots or pa tches.

Fever

y When a pathogen infects the body the hypothalmus resets to a higher temperature.y This helps the body combat infection in two ways

o Many pathogens reproduce effectively at 37oC. A higher temperature willreduce the effectiveness of pathogens to reproduce and so they cause less

damage

o The specific response system is more effecvtive at a higher temperature. 4 y In a bacterial infection the temperature rises steadily and remains high until

treatment is succcessful


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y A viral infection causes the temp erature to spike, shooting up high every time theviruses burst out of a cell and dropping back down to normals afterwards.

y Fevers can be beneficial but if they get too high they can be fataly If body temperature taises above 40 enzymes can denature and permanent tissue

damage can be caused

y Sweating is associated with fevers as a response to the high temeperature and chillsas the high temperature drops.

y If the fluid and electrolytes losr in t he sweat ar not replaced, dangerous dehydrationand death can result

Phagocytosis

y Phagocytosis involves white blodd cells called phagocytesy Phagotcyte describes a white blood cell which engulfs and digests pathogens and

any other foreign material in the blood and tissues.

y There are tow main types of phagocytes:o Neutorphils Granulocytes ( Have granules that can be stained in the

cytoplasm) Most abundant type ofWBC

o Macrophage Agranulocytes (Do not have granules)y They accumulate at the site of infection to attack the pathogeny They can often be seen as pus.

Interferons

y Effective only against virusesy C

ells produce interferon chemicals when invaded by viruses.

y They are proteins that inhibit viral replication within the cells.y They bind to the receptors on the surface membrane of ininfected cells, stimulatin a

pathway which makes cells resistant to infection by preventing virus reproduction.

Antibodies

y An antibody is a protein which is relased into the circulation to bind to a specificantigen on a praticular pathogen which will then lead to its destruction.

y Each plasma cell secretes antibodies which are identical to the immunogloblin of theoriginal parent b-cell

y Plasma cells only live for a few days b ut can produce 200 antibodies per second.y Plasma cells have extensive endoplasmic reticulum and many ribosomes which are

adaptations for their role in producing large quantities of protein antibodies.

Antibodies play a role in the defence of the body in a range of ways:

y The ability of most pathogen to invade the host cells is rduced whrn theyarecombined with antibodies.


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y When antigens on the pathogens are bound to antibodies, the microorganismsagglutinate (clump together) and this prevents their spread t hroughout the body.

y The antigen-antibody complex is readily engulfed and digested by phagocytes.y The antigen-antibody complex may stimulate other reactions wthin the body.E.g.

release of histamines by the invaded cells causing inflammation.

Cell mediated response

y T-Killer cells kill cells of the body that have been in fected with a virus.y When a body cell is infecred with a virus, the antigens are bound to a MHC and the

cell becomes an APC

o T-killer cells in the blood have complementary receptor proteins on thesurface

o T-Killer cells bind to antigen/MHC complex on the body cell o T-Killer cells undergo rapid cell division to produce clones which can all bind

to infected body cellso T-Killers cells release enzymes creating pores in the membrane of infected

cells

o Pores creates free movement of water and ions, leading to swlling and lysiso Any pathogens are labelled with antibodies prouced by B effector cells and

then destroyed

o Some T-Killer cells becomes T-Killer memory cells.They remain in the bloodready to respon to the same antigen.

Why do we feel ill?

y The specific immune response takes days or even weeks to become active against aspecific pathogen

y We get symptoms of disease, when the pathogen is reproducing freely inside thebody, before the immune system becomes fully operational isnside in the body

against the pathogen.

Gaining knowledge competition bacterial antibiotics and Hosptial acquired disease

1. Asepsis is the absence of infectious organisms, and aseptic techniques are aimed atminimising infection.

2. Ignaz semmelweis substancially reduced the number of childbed fever byencouraging doctors to wash their hands between deliveries and examinations.

Jospeh Lister faught infection using pure phenol as an antiseptic.Fleming discovered

penicillin accidently and Florey and Chain developed it for mass production.

3. Differene between antiseptic and disinfectant is that disinfectants are chemicalsused to destroy bacteria in the environment, whereas antispetics are used directly

on people.


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4. Antibiotics reduced the number of deaths from infectious disease by being able totreat patients already suffering a bacterial infection.

5. The principle of selctive toxicity is that the drugs interfere with the metabolism orfunction of the pathogen with minmal damge to the human host

6. The difference between bacteriostatic and bacteriocidal is that bacteriostatic willcom[;etely inhibit the growth of the microorganism wheras bacteriocidal will destroy

almost all of the pathogens present.Bacteriostatic antibiotics are usually used to

treat normal everyday infections because, combined with the immune system it will

ensure the pathogen will be completely destroyed.Bacte riocidal antibiotics will be

used when the immune system has been supressed.

7. Broad spectrum antibiotics destroy a wide range of harmful bacteria pathogens,neutral and good bacteria alike. A narrow spectrum antibiotic targets one or two

specific bacteria.

8. Pathogens are completely destroyed if they are sensitive if increased dose andtreatment more succesful pathogen is moderatly sensitive. Antibiotics do not affect

pathogen which means they wuill be resistant.

9. Only a few microorganisms are resistant .When non-resistant are killed, theresistant strain multiply and create a resistant infection.

10.The spread of superbugs is accelerated by widespread use of antibiotics, increasingtheir resistance.

11.Superbugs are usually found in hospitals because many people are ill and antibioticsare widely used.

12.MRSA is found in hospitals, it stands for methicillin resistant staphilococcus aureus.Itis a healthcare acquired infection. A mutation arose to cause the bacteria to be able

to produce a penicillinase that breaks down the methicillin13.C difficile is an anerobic bacteirum that is found in small numbers in the large

intestine. Not affected by many antibiotics.

14.The symptoms or MRSA are:y septicaemia (blood poisoning),y septic shock (widespread infection of the blood that leads to a fall in blood pressure and

organ failure),

y septic arthritis (severe joint problems),y osteomyelitis (bone marrow infection),y abscesses deep within the body,y

meningitis,y pneumonia, ory endocarditis (infection of the heart lining).The symptoms ofC.Dificile:

y mild to severe diarrhoea

y blood-stained stools

y fever


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y cramps in the abdomen

15.Antibiotics should be used sparingly because overuse can cause bacteria to become resistantmuch more quickly.Course of antibiotics should always be completed. Limit the typres of

antibiotics used.

16.Hygiene measures :a. Wash hands with alcohol based gels between patients for MRSAb. Chlroine based disinfectant needs to be used to avoid trhw spread ofC.Dificilec. Long ties, wristwatches and long-sleeved shirts are banned .These can carry bacteria

from 1 patient to another

d. Thorough cleaning of hospital wards, toilets and equipments such as bedpans canalso control the spread of disease.

e. Isolate infected patients.Spread can be controlled in this way.17.Patients may be screened for MRSA and other infections.They can be treated immeiatel.

Hospital adivse people not to visit if they are unwell . Visitors are encourages to wash their

hands and use the alcohol gels provided.

18.30% decrease in the incidence ofMRSA. Yes hygiene measures havebeen effective.C dificliecases have laso decreased.

Immunity

4 types Natural active and passive

Artificial active and passive.

HIV and Tuberculosis

Unit 4 Mrs Goodall

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Transcript of Unit 4 Mrs Goodall