post mortem changes Flashcards
early post mortem changes -
temperature degradation hypostasis (colour change) rigor mortis (stiffening)
late post mortem changes - 4
decomposition and autolysis
mummification
adipocere
skeltonization
post mortem changes
confirm death - indisputable evidence, resuscitation is futile
allows estimate of time of death
produce confusing artefacts
destroy evidence of identity, injury and disease
have specific forensic uses
sequence of post mortem changes
hours: algor mortis, livor mortis, rigor motris
days - wks: putrefaction
mths: skeletonisation, mummification
algor mortis
chill of death
useful indicator of post mortem interval (PMI) in first 24 hrs
only in temperate and cool climates
requires a core body temp: rectal (not in sexual abuse cases), liver (subcostal stab)
loss of heat from the body due to conduction, convection and radiation
little heat lost by evaporation
external surface cools quicker than internal organs
rapid cooling initially until body temp is equal to atmospheric temp
rate of cooling depends on
body size environmental temperature drafts and humidity clothing and coverings flooring immersion
effect of body size on cooling
larger SA = greater heat loss
obese individual will cool quicker
effect of environmental temperature on cooling
day to night fluctuations
sunny vs overcast
timed heating in a house
effect of drafts and humidity on cooling
body found outdoors or indoors near an open window will cool quicker than a body found near a heat source or in the sun
effect of clothing and coverings on cooling
body in multiple layers of clothing and under bedding will cool slower
effect of flooring on cooling
person on a tiled floor will cool more rapidly than someone on a carpet
effect of immersion on cooling
body cools quicker in water than in air
body temp at time of death
normal = 37C
lower body temp: hypothermia, cardiac failure, haemorrhage
higher body temp: heatstroke, fever, exercise, drugs
hessenge’s normogram
based on mathematical cooling model
allows for correction for: body weight, clothing, drafts, immersion
assumptions: normal body temp at death, no variation in ambient temp
exclusions to using hessenge’s normogram
nearby strong heat source
nearby cooling source
surface between body a strong conductor of heat
abnormal body temp at death
body moved between death and temp reading
livor mortis
darkening of death
pink/purple skin discolouration
can be seen prior to death
gravitational pooling of blood in blood vessels due to cessation of circulation - forms horizontal fluid level
evident within internal organs
compression of tissues prevents formation –> contact pallor where blood cannot pool
livor mortis and indication of PMI
variable interval prior to visibility
may appear before death
development delayed and intensity affected by natural disease, blood loss and poisoning
may not be evident in all but some cases
liver mortis timescale
<6hrs: incompletely formed, blanching, unfixed (can shift if body is moved - 1y pattern fades and 2y pattern develops)
10-24hrs: well established, partially fixed, blanching to finger pressure (1y pattern fixed enough to remain, 2y pattern also develops - dual distribution)
> 24 hrs: full established, fixed (1y pattern persists, no 2y pattern develops regardless of any movement)
rigor mortis
stiffening of death
decrease in ATP post mortem means actin-myosin bonds can’t break –> rigor mortis
Ca build up PM promotes actin-myosin cross bridging
rigor suspended by decomposition
doesnt develop until ATP reserve is completed (within hours after death)
sequence of onset of rigor mortis
develops in all muscles
smaller muscles usually become completely involved sooner than large ones
not necessarily constant or symmetrical
rate of development of rigor mortis
onset and development dependent on:
- body temp at time of death (hyperthermia increases onset)
- ambient temp: (occurs sooner in warmer temps)
- muscle activity prior to death: in times of high intensity exercise, quicker onset
disappearance:
- decomposition
- breaking: if a limb is forcibly stretched out during autopsy, rigor doesn’t redevelop in these areas
rigor mortis timescale
warm and w/o rigor: <3hrs PM
warm and w/ rigor: 3-8 hrs
cold and w/ rigor: 8-36 hrs
cold and w/o rigor: >36 hrs
later changes of decomposition
indisputable signs of death
resuscitation attempts futile
autolysis and putrefaction
define autolysis
enzymatic breakdown of cells/tissues
define putrefaction
bacterial breakdown of cells/tissues
what are the 5 types of decompositon
maceration wet putrefaction skeletonisation adipocere mummification
what is maceration
sterile autolysis of foetus that has died in utero
no exposure to maternal or environmental bacteria
wet putrefaction
enzymatic and bacterial
adipocere
saponification of soft tissues
requires wet conditions
mummification
desiccation of soft tissues
requires cool, dry conditions
putrefactive bacteria
temperature dependent (optimal at 21-38C)
mainly commensal bacteria from GI and resp
pathogenic bacteria: organ/tissue infection, septicaemia
sequence of putrefaction
- green discolouration of lower abdomen - overgrowth of colonic bacteria (2 days)
- green-black discolouration and swelling of face and neck - gas production from bacteria (3-4 days)
- red-brown purge fluid from nose and mouth
- gas production causes diffuse swelling of the body, most noticeable in the abdomen (methane, hydrogen, hydrogen sulphide, ammonia ptomaines)
- skin slippage and blistering, hair slippage from scalp (days to a week)
- marbling - breakdown of Hb in blood vessles, prominence of blood vessels on skin (days to a week)
rate of putrefaction is hastened by
slow initial cooling (clothing, bedding, obesity) warm environment high humidity fever at time of death infection wound/tissue disruption
rate of putrefaction is delayed by
rapid initial cooling (prompt refrigeration, immersion in cold water, low body mass) cold environment dry conditions hypothermia at time of death blood loss embalming burial
mummification
takes months - years
desiccation of tissues in dry conditions (can be warm or cool)
skin dries, shrinks and becomes leathery
internal organs may decompose or be preserves
more common in infants
adipocere
saponification - grave wax
moist conditions (submerged or water logged area)
transformation of body fat to oleic, palmitic and stearic acis by hydrolysis - predominates in fatty tissues
appears yellow/white/brown and waxy
rare
caused by clostridium welchii (anaerobic)
released FA inhibit other bacteria
weeks to months
affords some preservation of tissues
