Decomposition Flashcards
PM changes and TSD
Orderly physico-chemical
changes after death
Each change has its own time factor or rate
The longer the PMI, the less precise is the estimate of the time of death
PM changes in eyes
Loss of corneal and light
reflex
Fixed (mid dilated), unreactive pupils
Decrease in eyeball tension
Feels softer within minutes
after death
Loss of glistening
reflectivity of cornea
Discoloured sclera in open
eyes (yellow/brownish)
PM hypostasis
Skin discolouration
AKA: lividity, staining, cogitation and, liver mortis
PM hypostasis continued
Settling of blood after death
Gravity dependent
May see pale areas where
dependent portions in contact with firm surfaces or with tight clothing
Livor mortis colour
Red/purple colour
Cherry red/ pink livor seen in CO, cyanide, cold environment
Rare to see brown/ green livor
Livor mortis modification
Faint/inapparent livor in anaemic/ dark skinned individuals
Fixation time
Affected by temperature
Warmed= quicker
Cold= slower
Rigor mortis
The progressive stiffening of the muscles of the body
Stiffening starts in the small muscles and spreads down the body
Factors affecting right mortis
Environment temp
Degree of muscular activity before death
Rapid onset in children and age than in muscular young adults
Develops early and passes quickly in deaths from infections or from wasting diseases
Delayed in asphyxia deaths
Spot checks in average temp conditions
Body feels warm and flaccid: <3 hrs
Body feels warm and stiff: 3-8 hrs
Body feels cold and stiff: 8-36 hrs
Body feels cold and flaccid: >36 hrs
Cadaveric spasm
Muscular rigidity at the moment of death
Causes is unknown
Associated with violent deaths in intense emotions
Most commonly affects a
group of muscles only
Pugilistic attitude
Typical PM body position
Caused by coagulation of muscle proteins when body is exposed to very high temperatures
Common in burning victims
Algor mortis
Cooling of the body after death
Measure the core temperature (rectal or liver)
A measured rectal temperature can give some indication of the
time of death.
Algor motos modification
Persons age
Body mass and surface area
Physical condition
Initial temperature
Environmental
1 degree an hour is based on a normal room
temp environment
Body cooling
Body cooling is a physical process
Normally there is a temp plateau followed by linear cooling
Late PM period
When the body has been out for over 24 hours
Putrefaction
Environment impacts putrefaction
Begins when death occurs.
First changes affect the lower abdomen and green
discoloration of skin
Can appear as early as 24 to 36 hours
As bacteria multiplies, discoloration spreads upwards.
Bacteria causes the bloating as they produce gas. This is
seen in the face first
Decomposition fluids from nose and mouth. This is not
blood, but can be pinkish in appearance.
Adipocere
Parts of the body that contains fat
Occurs a month after death
It is the product of a chemical reaction in which fats react with water and hydrogen in the presence of bacterial enzymes
Adipocere (Sapponnification)
Weeks and months to form
Remains unchanged for years
A warm, moist, anaerobic environment favours adipocere formations
Skeletonization
Loss of tissue from the body
Extremely variable
Based on the environmental conditions and the o revende of insects and animals
Average rate is 1.5 years
Mummification
Dehydration of the tissues
The body shrivels and is converted into a leathery or parchment-like mass of skin
The internal organs are often decomposed but may be preserved
Skin shrinkage may produce large artefactual splits
Forensic entomology
Blowfly is the most common insect
Bluebottle the most frequent invade of dead flesh. Matures in 14-25 days (at 22°)
Beetles may arrive 3-6 months after death
Life cycle of a blowfly
Adult blowfly - Egg- 1st larval instar- 2nd larval instar- 3rd larval instar- pupa- Adult blowfly
Larval stages in blow fly cycle
1-2 days to start growning
4-5 days big in size
post-feeding larva 8-12 days
Pupa 18-24 days
Fresh stage
Blowfly and flesh flies are first to colonise a fresh corpse
Eggs are laid around the natural provoked and any wounds (warm, moist, well protected areas)
Bloated stage
Corpse begins to swell
Blowflies continue to ovipost
Maggots continue to feed
Rove beetles feed on fly larvae and eggs
Decay stage
Large masses of maggots still feeding externally and internally
Silphid, histerid and muscid beetles attracted to the corpse
Post-decay stage
Corpse is drying out
Reduction in number of flies
Increase in number of beetles
Dry stage
Skin and bone left
Insect with the ability to digest keratin move in
Caveat
Succession of different specifies in different climates differs significantly
If the indigenous species succession is not known then it is a lot more difficult to use succession as a means of PMI estimation
