injury to the body and post mortem changes week 10 Flashcards
what are the three injury classifications
- Sharp force
- blunt force
- ballistic
what kind of injuries are sharp force
- stabs
- incisions
what kind of injuries are blunt force
- abrasions
- bruises
- lacerations
what kind of injuries are ballistic
- explosions
- gunshots (rifle/shotgun)
what is an abrasion
- blunt force
- superficial injury to the epidermis
- crushing by vertical force (imprint)
- scraping by tangenital force (graze over broad surface e.g. road rash)
what is a contusion
bruise
what is a bruise
- blunt force
- crushing of the dermal blood vessels by mechanical impact causing leakage of blood from vessels into skin
what are the different types of presentations of bruises
- bruising of internal organs
- ‘tram-track’ bruising via rod, baton or plank-like object
- clustered discoid bruises via fingertip pressure
- black eyes via direct trauma or skull fractures
can you accurately age a bruise
no
what are lacerations caused by
- impact against a flat surface (scalp or facial laceration)
- impact by an edged or pointed object (brick, furniture corner, etc.)
- rotation of tissue on limb/torso (flaying injury), caused by revolving wheel/machinery
- excess frictional or tearing forces (senile skin tears, scalping)
what are incised wounds
- sharp force
- superficial sharp force injury caused by slashing motion
- injury is longer on the skin surface than it is deep
what are the features of lacerations
- caused by blunt force
- ragged margins
- marginal abrasion
- associated bruising
- tissue bridging
- slight bleeding
- trace evidence
what are the features of incisions
- caused by sharp force
- clean margins
- no associated abrasion
- no associated bruising
- clean division of tissues along wound tract
- profuse bleeding
- no trace evidence
what are the characteristics of chop wounds
- mix of sharp and blunt force
- abrasion with or without bruising of wound margins from wide blade
- incised edges crushed on entry of the thick blade
- variant of incision
- longer than it is deep
what are the early post mortem changes
- algor mortis (chill of death)
- livor mortis (darkening of death)
- rigor mortis (stiffening of death)
what are the late post mortem changes
- autolysis and putrefaction
- mummification
- adipocere
- skeletonisation
what is post mortem interval
the amount of time it has been since the person died
what is algor mortis
- loss of heat from the body due to conduction, convection and radiation and evaporation
- cooling occurs immediately after death (external surface (skin) will cool more quickly than interior (organs))
- rapid cooling of the body will occur initially until the body temp reaches the same temp as the atmospheric pressure then the rate of cooling is slowed down
- only in temperate and cool climates
- often unreliable, sometimes misleading
- may be useful indicator of PMI in the first 24 hours
what does the rate of cooling in algor mortis depend on
- body size, obese people will cool more quickly because of large surface area
- environmental temperature (fluctuations from day to night, sunny or overcast, heating in house)
- drafts and humidity (body found outdoors, indoors near window, body found in sun)
- clothing and coverings
- person on tiled floor will cool more quickly than carpet
- immersion (body cools more quickly in water than in air)
what is livor mortis
- seen as pinkish/purple discolouration
- gravitational pooling of blood in blood vessels due to cessation of circulation in death
- forms a horizontal fluid level
- evident within internal organs also
- compression of tissues prevents formation (contact pallor) where blood can’t pool e.g. bum if body lying on the floor will stay white bc compressed so no blood
- poor indicator of PMI
- may not be evident in all cases
- development delayed and intensity affected by natural disease, blood loss (e.g. anaemia) and poisoning
what is rigor mortis
- muscle fibre relaxation requires ATP to break actin-myosin bonds
- ATP requires oxygen
- decerase in ATP post mortem means bonds cannot break causing rigor mortis
- also calcium build up post mortem promotes actin-myosin cross bridging causing muscle contraction
- due to residual ATP in body, rigor mortis doesn’t develop immediately after death until ATP reserve is depleted i.e. within hours after death
what is the sequence of onset of rigor mortis
- develops in all muscles
- smaller muscles usually become completely involved sooner than the larger ones
- eyelids then jaw and neck, small joints of hands and feet, medium joints of arms and legs, large joints of shoulder and pelvic organs
what affects the rate of development of rigor mortis
- body temp at death (hyperthermia increases onset, hypothermia delays onset)
- rigor mortis occurs sooner in warmer temps
- muscle activity immediately prior to death (e.g. exercise means quicker onset of rigor mortis - probs bc less ATP)
- disappears with decomposition
- ‘breaking’, if arm or leg is forcibly stretched out during autopsy rigor doesn’t re-develop in these areas
what is autolysis
- enzymatic breakdown of cells/tissues
- cannot be seen to the naked eye
what is putrefaction
bacterial breakdown of cells/tissues
what are the types of decomposition
maceration - sterile autolysis of foetus, specific to foetus in uterus, no exposure to maternal or environmental bacteria
wet putrefaction - enzymatic and bacterial
skeletonisation
adipocere - saponification of soft tissues (requires wet conditions)
mummification - desiccation of soft tissues (requires cool, dry conditions)
what are the features of putrefactive bacteria
- temperature dependent (optimal 21-38 degrees)
- mainly commensal bacteria from GI or respiratory tract
- pathogenic bacteria (organ/tissue specific infection or septicaemia)
what is the sequence of putrefaction
- green discolouration of lower abdomen due to overgrowth of colonic bacteria (within 2 days)
- greenish black discolouration and swelling of face and neck due to gas production from bacteria (within 3-4 days)
- reddish brown purge fluid may extrude from the nose and mouth (don’t confuse with blood)
- gas formation causes diffuse swelling of the body, most noticeable in abdomen
- skin slippage and blistering, hair slippage from scalp (days to a week)
- marbling occurs due to breakdown of haemoglobin within blood vessels, prominence of blood vessels on skin (days to a week)
what speeds up putrefaction
- slow initial cooling
- warm environment
- high humidity
- fever at time of death
- infection
- wounds/tissue disruption
what slows down putrefaction
- rapit initial cooling
- cold environment
- dry conditions
- hypothermia at death
- blood loss
- embalming
- burial
what is mummification
- desiccation of tissues in dry conditions
- can take months to years
- skin dries, shrinks and leathery
- internal organs may decompose or be preserved
- more common in infants (great surface area to mass ratio)
- usually months but can start to occur within days to weeks if very arid conditions
what is adipocere (saponification)
- ‘grave wax’
- transformation of body fat to oleic palmitic, and stearic acids by hydrolysis
- appears yellow, white or brown and waxy; rare and occurs in humid or wet environments
- moist conditions (submerged, water logged grave)
- clostridium welchii causative bacteria
- released fatty acid inhibit other bacteria
- weeks to months
- predominates in fatty tissues
