body fluids Flashcards
do body fluids fall under biological or physical forensic evidence
biological
define bodily fluids
liquids ex/secreted by or present within the body at any given time
what is the difference between excreted and secreted
excreted = dispelled as waste from the body e.g. faeces, vomit, urine
secreted = transferred from one area of the body to another e.g. semen, sweat, saliva
name the 5 bodily fluids that are most important in forensics
blood
saliva
urine
faeces
semen
where are diatoms found and what can they tell us
found in the pleural liquid (liquid barrier around the lungs) and they can diagnose death by drowning
what can stomach contents/ vomit analysis tell us forensically
time of last meal, or if any poison has been ingested
what type of crime will leave behind more bodily fluids
violent
Give an example of direct and indirect transfers of the bodily fluid blood
direct - blood from victim to weapon during stabbing
indirect - blood splattering onto the nearby wall
why is it hard to detect many bodily fluids
as many are invisible
what are the two screening techniques used as crime scenes for bodily fluids
- ALS (alternative light sources) - relies on fluorescent properties in the fluid
- chemical agents (e.g. Luminol - screening agent for the presence of blood)
what are the 3 main stages in the forensic approach when testing for bodily fluids
- Presumptive tests - indicate potential source
- Confirmatory tests - conclusively identify type of biological material
- Downstream analysis - individual to identify offender - often uses DNA profiling
what is the most commonly encountered bodily fluid and why
blood - due to the volume we all have
what can a blood stain tell us about a crime and how
○ Who was involved? - DNA analysis
○ What happened? - e.g. clots in discovered blood shows a prolonged attack
○ When did it happen? - colour of blood
how many times thicker than water is blood
3-4x
what are the two main components of blood
plasma (55%) and cellular material (45%)
what can you find within blood plasma
water, antibodies, proteins, enzymes, hormones, amino acids, glucose and inorganic substances like drugs
what are the three main types of cells that make up the cellular material in blood
erythrocytes (RBC’s)
leucocytes (WBC’s)
thrombocytes (platelets)
which of the 3 main types of cells in blood is the most common
erythrocytes
what gives red blood cells their colour and why is this important forensically
haemoglobin - an iron-containing compound that carries O2 and CO2 - this is important as its haemoglobin that reacts with our presumptive tests to provide a positive result
what provides blood types characteristics (ABO)
antigens on the surface of red blood cells
what do leucocytes in blood contain that is important forensically
nuclei - DNA can be extracted and profiled allowing for identification of suspects
describe thrombocytes and what they do
irregularly shaped, colourless cell fragments that have a sticky surface in order to form clots to stop bleeding
what are the two important systems in the classification of blood
ABO and RhD antigen
who discovered the ABO blood typing system and when
Landsteiner in 1901
if a person is type A and does have the RhD antigen what’s their blood type
A+
what is an AB(O)H secretor and why is it important forensically
a person who secretes antigens into bodily fluids - this means that a persons blood group can be established from other fluids helping with exclusion/ inclusion of suspects
what are the three different types of bloodstains
- active bloodstains
- passive bloodstains
- transfer bloodstains
explain what an active bloodstain is, what it tells us and give examples
where blood travels by force other than gravity, e.g. impact to body via a weapon, projection from a punctured artery or a body falls onto an object that acts as a weapon. This can tell us the direction of travel on impact as well as the angle of impact
explain passive bloodstains, what they tell us and give examples
blood formed solely under influence of gravity, e.g. the pooling of blood after a head trauma. this can tell us the time since bloodshed via drying time as well as angle of impact
explain what a transfer bloodstain is and give examples
blood deposit = direct contact with contaminated objects e.g. from weapon or person (hand/footprints), disposal of evidence, etc.
what are the two types of presumptive tests use don bloodstains
screening tests - ALS
catalytic tests - Kastle-Meyer and LMG
what are the 4 confirmatory tests associated with blood
- Microscopic assessment of RBC’s and WBC’s
- Crystal tests
- UV-Vis spectroscopy
- Serological tests
what three glands in the mouth secrete saliva
sublingual, submandibular and parotid
how much saliva does a human produce everyday
1-1.5L
what makes up saliva
99% water and 1%; electrolytes, immunoglobulins, proteins, enzymes, WBC’s, etc.
what are the 4 main functions of saliva
- Lubrication and cleansing on the mouth
- Aids digestion as it breaks up food
- Anti-microbial properties
- Maintains oral hygiene
what are the presumptive tests for saliva based on and give examples
relies on enzyme activity analysis e.g. Phadebas, SALIgAE, RSID
why is speed important when detecting and identifying semen samples
as semen will naturally degrade - 31h in the mouth, 44h in the anus, 10days in the vagina, 19 days in the cervix
what are the two main components in semen
- cellular matrix
- complex fluid
what are the 3 key things to note about sperm cells for forensics
- flagellum - how they move
- Head - contains the genetic DNA
- Tip of head - contains an enzyme that allows it to enter an egg cell
what is the complex fluid component of semen made of and why is it important
proteins, acid phosphatase, prostrate specific antigens and albumin - important as the presence of acid phosphatase is how we presumptively test for semen
what are the 3 presumptive tests for semen
- ALS
- Test for seminal acid phosphatase
- Detect PSA (prostrate specific antigens)
what are the two confirmatory tests for semen
- Microscopic ID of sperm cells
- RS-ID semen test strip
why has vaginal fluid not got any accepted tests
as its not a well defined fluid as its composition changes during the menstrual cycle
how can menstrual fluid be analysed for a crime
the difference between peripheral and menstrual blood - trauma vs natural bleeding
what is an accepted presumptive test for menstrual fluid
SERATEC-PMB - the detection of haemoglobin and d-dimer
what is the composition of urine
91-96% water and the rest is inorganic salts and organic compounds
what can we test for in detection of urine
urea - detect ammonia via Nessler’s or DMAC reagent
creatinine - Jaffe test
THP-specific antigens - uses THP-specific antibodies
what is the least commonly found bodily fluid at crime scenes
sweat
name the 3 forensic tests for sweat
- SEM-EDX - for chlorine peaks
- G-81 monoclonal antibody (sweat specific) ELISA analysis
- Metabolite biometrics
name a few forensic values of bodily fluids
- Fluids important for context of case - source
- Downstream DNA analysis - enables robust identification
- Fast, efficient and inexpensive - saves time and money
- Allows sorting of evidence by relevance
- Body fluids analysis a major component of crime scene and lab processing
