bodily fluids: Flashcards
bodily fluids:
excreted- dispelled as waste from the body: faeces, vomit, urine.
secreted- transferred from one area of the body to another: sweat, blood/plasma, semen, saliva.
bodily fluids help determine how/when a victim died and who the offender was.
forensic pathology:
cause, manner and time since death.
eg- diatoms in the pleural liquid (liquid barrier around the lungs), stomach contents/vomit analysis, estimating time since death using vitreous humour (liquid in eye).
detection:
many fluids and stains are invisible. screening techniques can be used- alternative light sources (ALS), chemical agents (luminol, test for presence of blood). locate fluids in situ before collection.
forensic approach:
- presumptive test- indicate potential source.
- confirmatory tests- conclusively identify type of biological material.
- downstream analyses- individualise (DNA).
tests: vary by type of fluid, non destructive, scene based/lab based and avoid contamination.
blood:
most common bodily fluid encountered. volume recovered varies- drop, stain, pattern. detectable after cleaning attempts.
various presumptive tests available.
bloods nature:
viscous- 3-4x thicker than water.
55% plasma- water, antibodies, proteins, enzymes, hormones, amino acids, glucose and inorganic substances- drugs/alcohol.
45% cellular material.
blood function- erythrocytes:
RBCs, most common (44%).
contains haemoglobin (iron containing protein carries o2 and co2).
blood its colour. its shape allows it to be flexible for travel (no nucleus).
antigens on surface of RBCs which gives blood type characteristics.
blood function: leucocytes
WBCs. <1% blood volume. contain nuclei (DNA).
protect against infectious disease and invaders.
5 types of WBCs- granulocytes (neutrophils, eosinophils, basophils), lymphocytes, monocytes.
blood function- thrombocytes:
platelets and cell fragments. irregularly shaped, colourless- produced in bone marrow.
sticky surface which form clots to stop bleeding.
fluidity of the blood.
active when circulatory system walls damaged.
blood types:
classification of blood based on presence/absence of antibodies (plasma) and inherited antigenic substances (RBCs).
blood type inherited from both parents.
2 important systems- ABO and RhD.
ABO system:
denotes presence of 1, both, or neither A or B antigens on RBCs.
initially discovered by Landsteiner (1901).
4 main groups- A, B, O, AB.
phenotypes vary in different populations.
rhesus (Rh) system:
2nd most important blood group system.
50 defined blood groups including D, C, c, E.
initially discovered in monkeys by landsteiner and weiner (1930s).
RdH antigen- important and most immunogenic (+ present) (-absent).
84% of europeans RhD+ (A+, B+, O+, AB+)
AB(O)H secretors:
person secretes antigens into bodily fluids- saliva, urine, tears, bile, digestive fluids.
80% of caucasian population carry gene.
forensic importance- blood group established from other fluids, exclusion of non secretor, useful historically.
bloods forensic significance:
RBCs- identify blood group antigens, peroxidase like activity= detection.
WBCs- DNA analysis.
plasma- serum (species testing), drug/alcohol screening, BPA.
blood pattern analysis (BPA):
blood exits the body as a liquid.
exits differently depending on injury/action- flow, drip, spray, spurt, gush, ooze.
analysis of patterns- what happened/order of events.
- active bloodstains
blood travels by force other than gravity. impact to the body (weapon)- spatter. projection (punctures artery)- gushes or spurts. secondary object (weapon)- cast of stains.
direction of travel on impact- tails.
angle of impact- round/elongated.
- passive bloodstains
blood formed solely under influence of gravity.
blood flows often extensive- body position, has the body been moved post mortem
droops and pools= time since bloodshed- estimate drying time. angle of impact.
- transfer bloodstains
blood deposit= direct contact with contaminated objects.
from weapon or person (hand/footprints), disposing of evidence (wiping a weapon on clothing), indicate repeated contacts.
presumptive tests:
determine presence of trace levels, following clean up, tests unknown stains at crime scene and in lab.
presumptive tests: screening techniques
ALS/chemiluminescence (non visible traces)- polilight, luminol, flourescin, bluestar.
informs use of additional presumptive tests, rapid and non detsructive.
ALS used to detect variety of fluids.
luminol- relies on haemoglobin reacting to peroxidase through interaction with hydrogen peroxide in the luminol- most effective
presumptive tests- catalytic tests:
haemoglobin catalyses oxidation of reagents (h2o2)- changes colour if positive.
phenolpthalein (kastle meyer test- blood+ ethanol+ KM reagent+ hydrogen peroxide= pink) and leucgomalachite green (LMG).
will detect tiny amounts of blood but potential for false positives (things with iron in).
confirmatory tests:
absolutely identify unknown stain as blood. microscopic assessment of RBCs and WBCs.
crystal tests- teichman and takayama- formation of hematin/hemochromogen= crystals.
spectroscopy highly reliable- haemoglobin derivatives (soret absorbance band).
serological tests:
precipitin test= identify human proteins- does haemoglobin in blood react with anti human haemoglobin, repeat tests using antiserums for other species.
further forensic analysis on blood type- reaction of antisera with blood antigens.
associate/exclude individuals.
saliva:
non invasive control sample collection.
forensic analysis- identify the accused, detect drugs/alcohol, poisoning cases, hormone levels, species identification- animal bites