Lecture 6: Decomposition, stages and characteristics Flashcards
Decomposition
- Decaying caused by bacteria or fungal action
- Reduction of a whole organism to simpler forms of matter
- A continual process that can take weeks to years, depending on the environment
- A process that contributes to the cycling of energy and nutrients in the environment
- A process that is necessary for all life on earth
Taphonomy
- The study of the processes that affect the decomposition, dispersal, erosion, burial, and re-exposure of organisms after, at, and even before death
- The study of the processes of transition of organic life from the biosphere to the lithosphere (i.e. fossilisation)
The carcass/cadaver/body
-The carcass (cadaver/body) is the centre of a newly emerging microenvironment
-Cadaver decomposition Island (CDI)
Effect on vegetation
-Different plant growth can be visible for years
-Visible from the air: aerial photography
-Some species can be used as markers for mass graves e.g. wormwood (Artemesia Vulgaris) in the Balkans
-Can be used to search for clandestine graves (hidden graves)
Forensic taphonomy
- Forensic taphonomy is the study of the fate of human remains
- Scientific observations
- What happens to a body between death and subsequent recovery of the remains
- Can help understand and reconstruct the events surrounding a death
- PMI estimation
- Produce a timeline
- Further police enquiries
Stages of decomposition
- Decomposition is a continuous process
- Starts from the moment of clinical death
- Dependent on variables
- Traditionally divided into 5 categories:
-Fresh
-Bloat
-Active decay
-Advanced decay
-Skeletonization - Not linear
What regulates decomposition
Rate and Pattern of decomposition:
- Resources quality and composition
- Decomposers community
- Physiochemical environment
Mechanisms of decomposition
- Catalysis: enzymatic and chemical reaction transforming complex compounds into simple molecules:
-Bacteria
-Autolysis followed by
putrefaction - Communication: physical/mechanical breakdown of matter
-Insects, wind, sun, tides,
scavengers - Leaching: soluble material removed by water
Post-mortem interval (PMI) estimation
- Time since death
- Antemortem and postmortem data
- Evidence from the body
- Evidence from the environment
- Evidence from habits/ actions/ day to day activities
Why is PMI so important?
It has direct bearing on legal questions of alibi, opportunity, cause of death, and helps to implicate/eliminate suspects, potential motive, reconstruct sequence of events
Estimation
- Medicolegal time since death estimation must be reliable
- Reliability can only be provided empirically by statistical analysis of error in field studies
- Forensic scientists must provide:
-Evidence of their empirical
field studies
-Indication of reliability
-The error ranges
associated with their
estimates
PMI estimation methods
- Rate method:
-Measuring the change
produced by a process
which takes place at a
known rate which was
initiated or stopped by the
death. - Occurrence method:
-Comparing the occurrence
of events which took place
at known times with the
occurrence of the death
The rate method
Main principle of estimation of time since death= calculation from a measured value along a line/curve back to the initial value
Early PMI estimation (0-72 hours)
- Based on anatomical and physiological changes
- Temperature based methods
- Eye changes
- Muscle and tissue changes
- Gastric changes
Fresh stage- Typical traits
- Immediately after death, skin pales –> Pallor mortis
- Skeletal muscles relax- soiling and purging of stomach contents may occur
- Blood gradually becomes acidic due to the accumulation of carbon dioxide in the bloodstream
- Changes to body temperature, colour, and muscles begin to appear within 15-30 minutes
- Autolysis is the primary driver of decomposition
Autolysis
- Decomposition is primarily driven by autolysis: ‘self-digestion’ or ‘cell death’
- As circulation and respiration stop, cells are starved of oxygen
- Cells can no longer control their membranes –> cells are flooded
–>Cells swell and burst - Lytic enzymes burst out of cells and destroy surrounding tissue
The triad- Algor Mortis
> The cooling of the body after death -‘Newton’s law of cooling’
Approximately 0.78C per hour until the body reaches equilibrium with the environment
-Under ‘normal conditions’
Measured rectally or via the liver- most respective to core temperature –> most accurate within the first 24 hours
Other methods: Forehead, inner ear, full body, skin eyeball
Influencing factors:
-Ambient temperature
-Disease/ drugs
-Cause of death
-clothing
-Immersion in water
-Body size
-Dismemberment
Challenges:
-Rectal/liver temperatures
is invasive
-Positioning/mode of
measurement
-Many exceptions for
nomogram usage
-External Vs internal
contexts
-When ambient is above
average body temperature
The triad- Liver Mortis
- Livor mortis, hypostasis or lividity is considered the first identifiable taphonomic change characterised by deep pinkish red discolouration of the skin- although also occurs internally.
- Typically appears within the 30 minutes-1 hour after death, once the circulation system has ceased to function and gravity causes blood to settle I the dependent parts of the body.
- Body position indicates where the blood will settle as along the back and lower parts of the arms and legs if in a supine position or localised to the hands and feet if found hanging.
- Starts off patchy then these patches join together
- Blanching:
-Within the earlier stages,
the blood can be displaced
through pressure when
pressed with thumb or
spatula, also causing white
blanching, providing a
visual indicator of the
lividity’s progression
-After its peak around 3-6
hours the blood vessels
break down and the blood
disperses into the
surrounding tissues
causing fixed staining
around 8-12 hours
The Triad- Liver Mortis: Influencing factors
-Ambient temperature
-Disease/drugs
-Cause of death
-Clothing
The Triad- Liver Mortis: Challenges
-Darker skin tones
-Body deposition in water
-Movement of body after death
-Disease of OD= Heart failure/congestion
-Subjectivity
-Misinterpretation
-Different colours of the skin have different aetiologies
-Colorimetry and spectrophotometry- Quantification of lividity: measuring intensity of discolouration and luminosity of blanched areas
-Lividity is no longer useful/applicable once purification has begun and the blood cells and blood vessels have started to break down
The Triad- Rigor mortis
- Rigor mortis is the characteristic stiffening of the muscles after death –> after initial flaccidity
- Depletion of Adenosine Triphosphate (ATP) and a build-up of Latic acid and calcium in the muscle fibre
- Actin and myosin fibres remain linked
Cadaveric spasm
- Muscle stiffening sets in immediately
- Not the same as rigor mortis
- Circumstances where there is high tension/excitement
-Drowning
-Car crash
-Violent homicide- Muscles tense –> arms can be raised, fists can be clenched
- Tends to be just limb and extremities
Ocular changes
- Clouding of the cornea: 2-3 hours after death
- Open eyes Vs closed
- Influenced by environment
Gastric contents
- Morphology of the gastric contents can provide information on the composition of the last meal
-colour
-Volume
-Residual food
-Additional items e.g. pills - Combined with any
antemortem data regarding last meal - Samples taken at autopsy
Where the food is situated within the digestive system may also be informed
