post mortem changes Flashcards
Natural processes which occur after death
cardiovascular failure- O2 not being delivered to tissues results in cellular death
energy production ceases and body cools
circulating blood becomes stagnant and settles under effects of gravity
usual body defences fail and it can no longer inhibit proliferation of bacteria- putrefaction ensues
skin loses colour- due to lack of circulation
skin marbling- prominent marble-like pattern
When is the best opportunity following death to ‘time’ death?
The first 18 hours or so. However it is not possible to accurately time death
What is the most important factor for timing of death in the first 12 hours following death?
measuring body temperature
what shape of curve does the rate of cooling of a dead body follow?
sigmoid shaped curve (s -shaped) in theory
what factors influence rate of body cooling?
whether the body is clothed/nature of clothing
what the usual temperature is of that body and can it vary?
natural insulation of the body
convection currents
environmental temp
Even under the most favourable conditions what is the accuracy the best calculations can offer for a precise timing of death?
+/- 2.5 hours
What is the ‘rule of thumb’ in rate of body cooling?
1 degree Celsius an hour
Can the rate at which the stomach empties be a means of measuring timing of death? and why?
no because there are too many factors influencing the rate at which the stomach empties
What are the factors influencing the rate at which the stomach empties?
nature/amount of food
solids vs liquids
stress
certain medication
What is ‘Rigor Mortis’?
the stiffening and shortening of muscle fibres after death leading to rigidity of the musculature and fixation of the joints
Why does rigor mortis occur?
ATP levels reduce within muscles after death. All muscle fibres are affected
When to check for rigor?
8-12 hours after death usually rigor is fully established
What happens usually 36 hours after death?
the body returns to flaccid (loose) state
Is rigor mortis an accurate way to predict timing of death?
no, same fundamental problems as other methods. Too much biological variability.It is only of use in the first couple of days after death
What has an effect on rigor?
ambient temperature
What is ‘cadaveric spasm’?
rigor that occurs at time of death. Rare, instantaneous muscle stiffening. This persists through to rigor mortis.
What is putrefaction caused by?
Action of bacterial microorganisms. The process begins at death but takes period of time to become detectable.
Which variables need to be considered in putrefaction?
Ambient temp
humidity
‘cleanliness’ of environment in which the body lies
2-3 days greenish discolouration of abdominal skin (gut bacteria)
1 week blister formation, tissue swelling, gas formation in cavities
Example of an organ that is relatively resistant to putrefaction and why that’s useful.
Uterus. Useful for identification purposes
Mummification
when the body dries out. Common in infant bodies
Adipocere formation
a greasy/waxy material which frequently remains attached to bony skeleton. It is formed by decomposition of soft tissue of dead bodies usually those exposed to damp or wet environments ie bodies recovered from water
Skeletonisation
condition when all of the soft tissues of the body have completely degraded. Process is extremely variable.
Variables affecting skeletonisation
exposure to meat eating animals (post -mortem predation) e.g rats and to dipterous larvae
What is post mortem hypostasis/lividity?
pooling of stagnant blood in dependent cavities of the body under the influence of gravity. Begins as soon as circulation stops.
Blood lies where pressure is applied on body ie body lying on it’s back- blood will be in upper back and buttocks.
Is hypostasis or lividity helpful in determining timing of death?
no but may be useful in knowing the position of the body after death. Could also know if it had been moved as long as lividity was established before it was moved.
It may be hard to distinguish between hypostasis and…?
Bruising
Colour of hypostasis
usually pink/purple
Cherry red blood in hypostasis could mean?
an indicator of carbon monoxide posoning
Red/brown blood in hypostasis?
methaemoglobin (caused by certain chemicals/drugs)
Post mortem artefacts?
alterations or damage to body after death that actually mimic a genuine process occuring in real life. Ie water damage- bodies recovered from water- may mimic traumatic injury
what would dark blue-pink hypostasis indicate?
cyanide poisoning
