human decomposition: stages, characteristics and introduction to PMI Flashcards
decomposition:
decaying caused by bacteria or fungal action.
reduction of the body of a living 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 science of the laws of embedding or burial. the study of the processes of transition of organic life from the biosphere to the lithosphere.
death, transport, deposition, preservation and modification
the carcass/ cadaver/ body:
the carcass is the centre of a newly emerging microenvironment. cadaver decomposition island (CDI). taphonomy helps to understand how the environment influences the CDI and how the cadaver influences the environment its deposited in.
effects on vegetation:
differential plant growth can be visible for years. visible from the air: aerial photography. some species can be used as markers for mass graves eg wormwood (artemisia vulgaris) in the balkans. can be used to search for clandestine graves.
forensic taphonomy
the study of the fate of human remains.
scientific observations.
what happens to a body between death and subsequent recovery of remains.
can help understand and reconstruct the events surrounding a death.
PMI estimation.
produce a timeline of events.
further police enquiries.
stages of decomposition:
decomposition is a continuous process. starts from a moment of clinical death. depends on many variables. 5 categories that happen- fresh (first 72 hours), bloat (build up of gases in abdominal cavity), active decay (insect activity), advanced decay (insect activity slows, more beetles and drying out of tissues), skeletonization (dry remains). not a linear process.
what regulates decomposition:
the rate and pattern of decomposition, order of the stages. resource quality and composition (size, fat distribution, is the hair present. decomposer community (bacteria, fungal), physiochemical environment (geographic location, water) (extrinsic factors).
mechanisms of decomposition:
catalysis- enzymatic and chemical reactions 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 post mortem data.
evidence from the body.
evidence from the environment.
evidence from habitats/ actions/ day to day activities.
PMI
PMI has a direct bearing on legal questions of alibi, opportunity, cause of death and helps to implicate/ eliminate suspects, potential motive, reconstruct sequence of events.
PMI 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: (most reliable) measuring the change produced by a process which takes place at at 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.
early PMI estimation:
(0-72 hours) based on anatomical and physiological changes.
temperature based methods- henssge nomogram, algor mortis, application of algorithms or a combination of these methods.
eye changes- vitreous humour.
muscle and tissue changes- rigor mortis, livor mortis, mechanical/electrical excitability.
fresh stage typical traits:
immediately after death, skin pales- pallor mortis.
skeletal muscle relax- soiling and purging of stomach contents may occur.
blood gradually becomes acidic due to the accumulation of co2 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 stops, cells are starved of o2. 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- newtons law of cooling.
approximately 0.78C/1.5C per hour until the body reaches equilibrium with the environment- under normal conditions. measured rectally or via the liver- most representative of core temperature and is most accurate within the first 24 hours.
other methods- forehead, inner ear, full body, skin, eye.
most popular and most extensively researched area of PMI estimation.
henssge nomogram:
newtons law of cooling, post mortem plateau.
henssge created 2 nomograms, 1 for ambient temperature up to 23C and 1 for temp above 23C.
algor mortis influencing factors
ambient temp- heat slows cooling, cold accelerates.
cause of death- blood loss, extreme trauma.
clothing- extensive layers or coverings act as insulation.
immersion in water- water accelerates progression.
body size- surface area to volume ratio.
dismemberment- limb vs trunk, blood loss.
the triad- livor mortis:
the first identifiable taphonomic change characterised by deep pinkish red discolouration of the skin. although it also occurs internally.
typically occurs 30mins- 1hr after death, once circulation has ceased to function and gravity causes blood to settle in the dependent parts of the body. starts off patchy then these patches join together.
livor mortis- blanching:
skin in direct contact with a surface such as the floor or clothing will cause compression of the vessels and displacement of blood, leading to paler blanched areas.
within the earlier stages, the blood can be displaced through pressure when pressed, causing a white blanching, providing a visual indicator of lividity’s progression.
after its peak around 3-6 blood vessels break down and the blood disperses into the surrounding tissues causing fixed staining at around 8-12 hours.
confluence- patches joining.
livor mortis- influencing factors/ challenges
clothing- unusual patterns/ tight clothing prevents formation.
darker skin tones.
movement of body after death.
subjectivity,
misinterpretations- lividity vs marbling.
body deposition in water- reduced gravity= diffuse lividity.
colorimetry and spectrophotometry-quantification of lividity. measuring intensity of discolouration and luminosity of blanched areas.
lividity is no longer useful once putrefaction has begun, and all the blood cells and blood vessels have started to break down.
the triad- rigor mortis:
characteristic stiffening of the muscles after death after initial flaccidity. depletion of ATP and a build up of lactic acid and calcium in muscle fibre. actin and myosin fibres remain linked producing rigidity.
nystens rule- when a body is lying in the supine position: rigor mortis begins in the mandible, moving down to the neck, then to the trunk and extremities. noticeable in the wrist and ankle.
onset begins within 2-6 hours of death, peaking at 12 hours, and becoming resolved within 36 hours.
electrical excitability of muscle.
cadaveric spasms:
muscle stiffening sets in immediately. not the same as rigor mortis.
circumstances where there is high tension/excitement- drowning, car crash, violent homicide.
muscle tense- arms can be raised, fists can be clenched. tends to be limbs and extremities.
ocular changes:
clouding of the cornea: 2-3 hours after death. open eyes vs closed eyes.
tache noir- drying out of the corneal surface where the eye was slightly open. black/red discolouration.
influenced by the environment= dry conditions accelerates development.
gastric contents:
morphology of the gastric contents can provide information on the composition of the last meal- colour, volume, residual food, pills. samples taken at autopsy.
liquids leave the stomach more rapidly than solids. carbs, proteins and lipids leave the stomach in that order. 4-6hrs the stomach will empty into the small intestine and 12hrs for food to leave the small intestine. 24hrs from when a meal was eaten until all undigested food is released from the large intestine.
gastric contents: influencing factors
diets- vegan
medication
surgery- gastric sleeve
disease/drugs- alcohol, diabetes, chrohns, IBS
human variation- metabolism, exercise
subjective
