decomposition Flashcards
define decomposition
the decay of organic matter caused by bacteria or fungal action OR the reduction of the body of a living organism to simpler forms of matter
what is very important to remember when discussing decomposition
it is highly variable
what is taphonomy
the study of the processes that affect decomposition, dispersal, erosion, burial, and re-exposure of organisms after, at and even before death
what is the carcass
the centre of a newly emerging microenvironment - also known as the cadaver or body
what is CDI and what does it demonstrate
cadaver decomposition island - the 2 way nature of decomposition
what effects can decomposition cause on vegetation
grass can appear more dull/ less green than normal above clandestine graves, and this can be visible for years - helpful for identification
what is forensic taphonomy
the study of the fate of human remains, including scientific observations of the body and the environment
what can forensic taphonomy provide
PMI estimations, a timeline of events, and answer further police enquiries
what are the 5 main stages of decomposition
- Fresh
- Bloat
- Active decay
- Advanced decay
- Skeletonization
for how long after stage does the fresh stage of decomposition last and what is it typified by
up to 72 hours after death - typified by the mortis triad
what is the bloat stage of decomposition typified by
the distention of the abdominal cavity due to the build up of gases
what peaks during the active decay stage of decomposition
insect activity
what does the process of decomposition depend on
intrinsic and extrinsic factors - making it non-linear
name 3 things that influence the rate and pattern of decomposition
- The resource quality and composition - the actual body and its size
- The physiochemical environment - weather conditions and if the body is in water or not
- The decomposer community - which bacterial and fungal species are present in the environment
what are the 3 mechanisms of decomposition
- Catalysis - enzymatic and chemical reactions transforming complex compounds into simple molecules
- Communication - physical/ mechanical breakdown of matter
- Leaching - soluble materials removed by water
what does PMI stand for in PMI estimation and what does it look at in regards to decomposition
Post-mortem interval - looks at a combination of both antemortem and post-mortem data e.g. evidence from the body, environment, habits/ actions, etc
why is PMI estimation important
it has direct bearing on legal questions of alibi, opportunity, cause of death, and helps to implicate/ eliminate suspects, potential motive and reconstruct the sequence of events
what must forensic scientists also provide with a PMI estimation
evidence of their empirical field studies, indication of reliability and the error ranges associated with their estimates
what are the two methods for PMI estimation
rate method and occurrence method
explain the rate method for PMI estimation
measures the change produced by a process which takes place at a known rate which was initiated or stopped by the death e.g. looking at chemical changes, insect lifecycles, etc.
explain the occurrence method of PMI estimation
comparing the occurrence of events which took place at known times with the occurrence of death e.g. must’ve been after a phone call - provides something that can be measured to provide statistical analysis, therefore is the most reliable
what is early PMI estimation based on and give a few examples
based on anatomical and physiological changes e.g. the mortis triad, eye changes (Viterous Humour), and gastric contents
what is Pallor mortis
when the skin pales immediately after death
why does blood gradually become acidic in the fresh stage of decomposition
due to the accumulation of carbon dioxide in the bloodstream as respiration has ceased
what is autolysis and why does it occur in the early stages of PMI
autolysis is self-digestion or cell death and it occurs due to circulation and respiration stopping after death.
what are the three types of mortis that make up to the mortis triad
Algor, liver and rigor mortis
what is Algor mortis
the cooling of the body after death that follows ‘Newtons law of cooling’ - an initial plateau, and then a decrease of around 0.78 degrees per hour
which of the mortis triad is the most reliable and why
Algor mortis as it is the most extensively researched area of PMI estimation
what can we use to estimate PMI using algor mortis and body temperature in comparison to ambient temperature
the Henssge nomogram
what is the major disadvantage to the Henssge nomogram
has a lot of caveats where it cannot be used, e.g. no strong radiation, no strong fever or hypothermia, no uncertain severe changes in the cooling, etc.
name 7 influencing factors of algor mortis
- ambient temperature
- disease/ drugs
- cause of death
- clothing
- immersion in water
- body size
- dismemberment
what is liver mortis
also known as hypostasis or lividity, is the first taphonomic change characterised by deep pinkish red discolouration of the skin
when does liver mortis typically appear
within 30-60 minutes after death - once circulation has stopped and gravity causes blood to settle in the dependent parts of the body
what is the supine position
laying on your back
what causes pale/ blanched areas instead of the pinkish discolouration in regards to liver mortis
direct contact with a surface such as floor or clothing will cause compression of the blood vessels and displacement of blood
how can blanching help with PMI estimation
if an area of discolouration has pressure applied to it and then it becomes blanched this can indicate not long since death as around after 8-12 hour since death the discolouration becomes permanent regardless of pressure
what are 4 influencing factors regarding liver mortis
- ambient temperature
- disease/ drugs
- cause of death
- clothing
what are a few common challenges regarding liver mortis
darker skin tones - as the discolouration is harder to see
body deposition in water - as gravity is reduced
movement of body after death
misinterpretation of bruising for discolouration
what is rigor mortis
the characteristic stiffening of the muscles after death
what causes rigor mortis
the depletion of adenosine triphosphate and a build up of lactic acid and calcium in the muscle fibre causes actin and myosin fibres to remain linked/ contracted
describe the timeline for rigor mortis
Warm and floppy <3 hours
Warm and stiff 3-8 hours
Cold and stiff 8-36 hours
Cold and floppy >36 hours
name one was we can test rigor mortis
electrical excitability of muscle
what is a cadaveric spasm and what can cause it
muscle stiffening setting in immediately after death - only occurs in circumstances where there is high tension/ excitement e.g. drowning, car crash or violent homicide
name 3 ocular changes that can help PMI estimation
- Clouding of the cornea - 2-3 hours after death
- Tache noir - the drying out of the corneal surface where the eye was slightly open
- changes to the Vitreous humour (jelly like substance in the eye) - uses changes in chemical composition as potassium levels increase with time since death
how do we use gastric contents in regards to PMI estimation
the morphology of the gastric contents can provide information on the composition of the last meal which can be combined with any antemortem data regarding last meal
name 6 influencing factors regarding gastric contents for the use of PMI estimation
- Habits/ specific diet
- Medication
- Surgery
- Disease/ drugs
- Human variation
- COD
