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Forensic science module > Lecture 7: Bodily fluids > Flashcards

Lecture 7: Bodily fluids Flashcards

1
Q

Bodily fluids

A
  • Liquids ex/secreted by or present within the body at any given time
    -Excreted –> e.g. faeces,
    vomit, urine
    -Secreted –> e.g.
    blood/plasma, semen,
    saliva
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2
Q

Forensic applications

A
  • Within the human body
  • Transferred to victim/scene
  • Help forensic scientists determine:
    -How/When a victim died
    -Who the offender was
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3
Q

Forensic pathology

A
  • Cause, manner, and time since death
    -E.g. diatoms in the pleural
    liquid
    -E.g. stomach
    contents/vomit analysis
    -E.g. estimating time since
    death using vitreous
    humour
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4
Q

Fluids as evidence

A
  • ‘Every contact leaves a trace’
  • Direct vs indirect transfers
  • Often have to assume presence
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5
Q

Forensic value

A
  • Present at various crime scenes
  • Persistence overtime
  • Detection + identification= DNA analysis
    -Individualisation
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6
Q

Detection

A

> Many fluids and stains are invisible
Screening techniques at scene
-E.g. alternative light
sources (ALS)
-E.g. chemical agents
(luminol)
Locate fluids ‘in situ’ before collection

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7
Q

Forensic approach

A
  1. Presumptive tests: indicate potential source
  2. Confirmatory tests: conclusively identify type of biological material
  3. Downstream analysis: individualise (DNA)
    * Tests:
    -Vary by type of fluid
    -Non-destructive
    -Scene-based/lab based
    -Avoid contamination
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8
Q

Collection

A

> Scene, evidence, and/or persons
-Documentation
-Sensitive techniques-
swabs, tapes, cuttings
Comparison samples (controls)
Measures to avoid cross-contamination

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9
Q

Blood

A

> Most common bodily fluid encountered
-Murder, assault, burglary,
sexual offences, hit and run
Volume recovered varies- drop stain, pattern
Detectable after cleaning attempts
Various presumptive tests available

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10
Q

Uses of blood

A
  • Forensic reconstruction
    -Who was involved?
    -What happened?
    -When did it happen?
    -What evidence is needed
    from suspects?
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11
Q

Nature of blood

A

> Viscous- 3-4x thicker than water
55% plasma
-Water, antibodies,
proteins, enzymes,
hormones, amino acids,
glucose ….
-Inorganic substances=
drugs/alcohol
45% cellular material

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12
Q

Function of blood

A

> Erythrocytes
Leucocytes
Thrombocytes

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13
Q

Erythrocytes

A

> RBCs –> Red Blood Cells
Most common (44%)
Contain haemoglobin
-Iron containing protein
carriers O2 and CO2
-Gives blood its colour
Shape= flexibility for travel
Antigens on surface of RBCs
-Blood-type characteristics

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14
Q

Leucocytes

A

> WBCs –> White Blood Cells
4% blood volume
Contain nuclei= DNA
Protect against infectious disease + invaders
Five types of WBC
-Granulocytes (neutrophils,
eosinophils, basophils)
-Lymphocytes
-Monocytes

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15
Q

Thrombocytes

A

> Platelets
Cell fragments
Irregularly-shaped, colourless- produced in bone marrow
Sticky surface- forms clots –> stops bleeding
Fluidity of the blood
Active when circulatory system walls damaged

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16
Q

Blood types

A

> Classification of blood based on presence/absence of:
-antibodies (plasma)
-Inherited antigenic
substances (RBCs)
Blood type inherited from both parents
Two important systems:
-ABO
-RhD antigen

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17
Q

ABO systems

A

> Denotes presence of one, both, or neither A or B antigens on RBCs
Initially discovered by Landsteiner (1901)
Four main groups- A, B, O, AB
Phenotypes vary in different populations

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18
Q

Rhesus (Rh) system

A

> 2nd most important blood group system
50 defined blood group antigens incl. D, C, c, E and e
Initially discovered by Landsteiner and Weiner (1930’s) in monkeys
RhD antigen- important and most immunogenic
-Present (+), absent (-)
84% of Europeans RhD+ (ie A+, B+, O+, AB+)

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19
Q

AB(O)H secretors

A

> Person secrets antigens into bodily fluids
-Saliva, urine, tears, bile,
digestive fluids etc
80% of Caucasian population carry gene
Forensic importance:
-Blood group established
from other fluids
-Exclusion of non-secretor
-Useful history

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20
Q

Forensic significance of blood

A

> RBCs:
-Identify blood group
antigens
-Peroxidase-like activity=
detection
WBCs:
-DNA analysis
Plasma:
-Serum (species testing)
-Drug/alcohol screening
-BPA

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21
Q

Blood pattern analysis (BPA)

A

> Blood exits in the body as a liquid
Exits differently depending on injury/action
Analysis of patterns- what happened? Order of events?
Violent crime- Often copious amounts of blood

22
Q
  1. Active bloodstain
A

> Blood travels by a force other than gravity
-Impact to body (weapon)-
spatter
-Projection (punctured
artery)- gushes or spurts
-Secondary object
(weapon)- cast off stains
Direction of travel on impact
-Tails
Angle of impact
-Round Vs elongated

23
Q
  1. Passive Bloodstain
A

Blood formed solely under influence of gravity
> Blood flows often extensive
> Drops and pods
> Angle of impact

24
Q
  1. Transfer Bloodstains
A

Blood deposit= direct contact with contaminated objects
> From weapon or person
> Disposing of evidence
> Indicate repeated contacts

25
Presumptive tests for blood
* Determine presence -Trace levels -Following clean up -Test unknown stains -At crime scene and in lab 1. Screening techniques 2. Catalytic tests
26
1. Screening techniques for blood
> ALS/chemiluminescence (non-visible) traces -E.g. Polilight, luminol, fluorescein, Bluestar > Informs use of additional presumptive tests > Rapid + non-destructive > ALS used to detect variety of fluids
27
2. Catalytic tests for blood
> Haemoglobin catalyses oxidation of reagents (e.g. H2O2) -Changes colour if +ive > Phenolphthalein (Kastle-Meyer tests) and leuchomalachile green (LMC)
28
Confirmatory tests for blood
> Absolutely identify unknown stain as blood > Microscopic assessment of RBCs and WBCs > Crytal tests- e.g. Teichman and Takayama > Spectroscopy highly reliable
29
Serological tests for blood
> Preciptin tests= identify human proteins > Further forensic analysis on blood type > Associate/exclude individuals
30
Saliva
> Common in burglary, assault, sexual offence cases -E.g. bite-marks -E.g. transferred to exhibits (balaclavas, cigarettes etc.) > Non-invasive control sample collection > Forensic analysis: -Identify the accused -Detect drugs/alcohol -Poisoning cases -Hormone levels -Species identification (animal bites)
31
Nature of saliva
> Digestive acid- breaks down food starches > Produced by 3 main glands (sublingual, submandibular, partoid) --> serous and mucus cells > Humans produce 1-1.5L/day > 99% water with pH of 6.8-7.0 -1% electrolytes, immunoglobulins, proteins, enzymes, nitrogenous products, WBCs …. >>including digestive enzyme: alpha amylase
32
Function of saliva
> Lubrication and cleansing of the mouth > Aids digestion: -Broken up food= bolus -Solubilise dry food -a-amylase= breaks down starch -Salivary lipase=fat digestion > Anti-microbial properties- e.g. lysozyme >Maintains oral hygiene
33
Forensic analysis of saliva
> Few well known and accepted presumptive tests -Enzymatic methods -ALS screening > No currently used confirmatory tests specific to saliva
34
Enzyme analysis of saliva
> Saliva ID based on presence of amylase enzyme -Phadebas, SALIgAE, RSID > Sample of stain added to soluble starch solution, iodine added as regent > Not specific for human saliva > High false +ive rate
35
Semen
> Evidence in sexual offence cases -Person (clothing, swabs, combings, hair, blood) -Scene (e.g. used condoms, bedding, furniture) > Speed important- medical exam of victim -Detectable up to 31 hr (mouth), 44 hr (anus), 10 days (vagina), 19 days (cervix) > Aim: identify/exclude a suspect
36
Nature of semen
> Complex fluid and cellular mixture produced by male reproductive glands 1. Cellular mixture= spermatozoa -Reproductive cells carry genetic material for sexual reproduction 2. Complex fluid= seminal fluid -Protective, nutrient rich environment for sperm cell post-ejaculation > 15-30% from the prostate: proteins incl. acid phosphase, prostate-specific antigens & albumin > 5% from epididymis & testis: sperm rich fluid > 60-75% from seminal vesicles: hormones, proteins (coagulants, fructose, glands)
37
Function of semen
> Sexual reproduction in humans/animals > Contributes half of genetic information to offspring > Average ejaculate 2-6ml -100-150 million sperm cells/ml > Alkaline pH 7.2-7.6
38
Forensic analysis of semen
1. Presumptive tests > ALS- but not all semen fluoresces > Tests for seminal acid phosphate (SAP) most common -If present, AP will react with alpha-naphthyl phosphate > Detect PSA (prostate specific antigens) e.g. p30 -Present in seminal plasma= antibody-antigen reactions 2. Confirmatory tests > Microscopic ID of sperm cells -Treated with stain to visualise heads -Christmas tree stain: >>Nuclear Fast Red- nuclei >>Picroindigocarmine- tails > RS-ID semen strip test -Sensitive & specific -Seminal vesicle-specific antigen- semenogelin -Pre-ejaculation fluid also
39
Vaginal fluid
> Not as common at crime scenes as blood, semen, saliva > Important role in sexual assault cases > Very few tests as fluid is not well defined -Composition varies due to menstrual cycle -Variable hormone levels
40
Nature and function of vaginal fluid
> Vaginal secretions = mucus or fluid produced from cervical & vaginal glands > Average production- 6g/day > Protects from microbial/bacterial infections > Proteins incl. lysozyme, acid phosphase, amylase > Shed blood cells, urea, epithelial cells…
41
Presumptive tests for vaginal fluid
> No presumptive/confirmatory test routinely used > Detect glycogenated epithelial cells with periodic Acid-Schiff (PAS) reagent -Stains cytoplasm magenta -Reliability? Destructive? -Rogers et al (2020) > Lactic/citric acid ratio- VF or semen?
42
Menstrual fluid
> Need to distinguish between peripheral & menstrual blood > Importance of context within the case- trauma? Natural bleeding? > Challenging distinction to make- new techniques developing (2017+) > SERATEC-PMB- detect haemoglobin and d-dimer > Quick, easy to use, preserves DNA > Forensic validation- assess effectiveness: 1. specific and sensitive (3ul) 2. Different treatment time based on age of sample 3. No false +ves or -ves (ages, mixtures) 4. Post-mortem +ve samples 5. DNA extracted- sample buffer and sample well 6. Successfully applied to case work samples
43
Urine
> Useful in (sexual) assault, harassment, drug, mischief, abuse cases > Difficult to detect -Low sensitivity of available tests -False positive results > Less viscous than other fluids- dispersal, dilution > Odour not localised
44
Nature and function of urine
> Liquid by-product of the metabolism > Expels nitrogen rich by-products: urea, uric acis, creatinine > Average production: 1.4L/day > 91-96% water -Inorganic salts & organic compounds (e.g. proteins, hormones, metabolites) -solids (e.g. urea)
45
Forensic tests for urine
> Diluted urine- limited ALS detection > Urea: activity of the enzyme urease -Breaks down urea, releases ammonia + CO2 -Detect ammonia via Nessler's or DMAC reagent > Creatinine: high concentrations -Jaffe test= creatinine reacts with picric in alkaline medium > Limited efficiency with dried stains..
46
RSID urine test
> Tamm-Horsfall (THP) most abundant protein- 50-100mg/day excreted > Specific to urine but concentration varies -Test= assay uses THP- specific antibodies -In-situ sampling increases test sensitivity -Blood presence inhibits urine detection -Not human specific
47
Sweat
> Less common bodily fluid found at crime scenes > Useful evidence in range of forensic cases > DNA evidence- extracted from hats, clothing, bedding etc,
48
Nature and function of sweat
> Fluids secreted by sweat glands in skin > Means of thermoregulation > Sweat rates up to 2-4L/hr or 10-14L/day > Mostly water with dissolved mineral traces -Lactic acid -Urea, creatinine -NA, K, Ca, Mg
49
Forensic tests for sweat
> Most difficult of bodily fluids to identify 1. SEM-EDX: chlorine peak basis of comparison 2. G-81 monoclonal antibody (sweat-specific) ELISA analysis 3. Metabolite biometrics: single-analyte enzymatic assays distinguish persons > Additional forensic intelligence- drug use, alcohol consumption
50
Forensic value of bodily fluids
> Fluids important for context of case- source > Downstream DNA analysis- enables robust identification > Fast, efficient, inexpensive- saves time, money, effort > Allows sorting of evidence by relevance > Body fluids analysis a major component of crime scene and lab processing
51
Proteomics
> Protein analysis= advances within bodily fluid testing > Proteome: proteins coded in genetic makeup of individual (genome) -Study of all proteins in a cell (structure, modifications, interactions etc.) > May yield detailed profile of an unknown individual

Forensic science module (14 decks)

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