Topic 6 Flashcards
What can be examined to determine the time of death of a mammal?
Extent of decomposition
Stages of sucession
Forensic entomology
Body temperature
Degree of muscle contraction
What is the human core body temperature?
36.2°C-37.6°C
Why does body temperature drop when you die?
Heat-producing chemical reactions stop
How is core body temperature measured?
Via the rectum or through an abdmonal stab using a long thermometer
Why must a long thermometer be used to determine core body temperature?
An ordinary clinical thermometer is too short and has too small a temperature range
Aside from a long thermometer, what may also be used to measure core body temperature?
An electronic temperature probe
What must be noted when using core body temp to determine time of death?
Environmental conditions
They will affect how the body has cooled
What type of graph does the cooling of the body follow?
A sigmoid curve
(S-shaped curve)
After a person has died, how long does the inital temperature plateau last?
Between 30 and 60 mins
What does the sigmoid curve graph of body temp after death assume?
That the person’s body temp was the normal 37°C at the time of death
Why might someone’s core body temp not be the usual 37°C when they die?
They may have a fever or hypothermia, meaning their body temp will be higher/lower than normal
Which part of the sigmoid curve of body temp is used to estimate time of death?
The near-linear part
(the middle bit)
What does the near-linear part of the sigmoid curve show?
Temperature decline per hour
What factors affect post-mortem cooling?
Body size
Body position
Clothing
Air movement
Humidity
Temp of surroundings
If body is in water
Why do bodies immersed in water cool more rapidly than those in air?
Water is a better conductor than air
What does rigor mortis mean?
Literally ‘stiffness of death’
It is the stiffening of muscles after death
What happens to muscles after death?
They usually totally relax then stiffen
What happens to joins during rigor mortis?
Become fixed in position - either flexed (bent) or extended (straight)
What does the position of joints during rigor mortis depend upon?
The body position at the time of death
Describe + explain the process of rigor mortis
- After death, muscle cells become starved of oxygen and oxgen-dependant reactions stop
- Respiration in cells becomes anaerobic + produces lactic acid
- The pH of cells falls, inhibiting enzymes + thus anaerobic respiration
- ATP needed for muscle contraction no longer made, so bonds between muscle proteins become fixed
- Muscle proteins can no longer move over one another to shorten muscle fibre. Muscle + joints become fixed
Which muscles stiffen first during rigor mortis?
Smaller muscles, then larger ones
What causes rigor mortis to pass off?
Muscle tissue starts to break down
Which muscle tissue breaks down first?
How does this relate the the order in which rigor mortis develops?
Smaller muscles break down first
This is the same order in which rigor mortis developed
When will most human bodies have complete rigor mortis?
6-9 hours after death
What can cause rigor mortis to set in more quickly?
If enviromental temp is high
If the person has been physically active before death
If a body is warm and not stiff, what is the approximate time since death?
Under 3 hours
If a body is warm and stiff, what is the approximate time since death?
3-8 hours
If a body is cold and stiff, what is the approximate time since death?
8-36 hours
If the body is cold and not stiff, what is the approximate time since death?
36-48 hours
What is autolysis?
The destruction of cells or tissues by their own enzymes, especially those released by lysosomes as well as the digestive tract
Where do the bacteria that cause the body to decompose come from?
The gut + gaseous exchange system
(Some also from the surroundings)
What is the first sign of decomposition?
Putrefaction
What is putrefaction and what causes it?
Greenish discolouration to the skin of the lower abdomen
Caused by the formation of sulfhaemoglobin in the blood
Describe + explain the stages of decomposition
- Putrefaction occurs first in skin of lower abdomen. Then spreads to rest of body.
- Body then darkens to reddish-green, then turns purple-black colour.
- Gas/liquid blisters may appear on skin
- Body swells + becomes bloated due to formation of gases (hydrogen sulfide, methane, ammonia, hydrogen, and CO2) by bacteria
- As tissues further decompose, gas released + body deflates
- When fluid associated with putrefaction drains away, soft tissues shrink + decay rate of dry body reduced.
In average conditions, when will the discoloration of the abdominal wall occur?
36-72 hours post mortem
In average conditions, when will gas formation as a result of decomposition occur?
About a week post mortem
How does the temperature of the body deternine the rate of decompostion?
Occurs faster at warmer temps.
If body temp remains above 26ºC, gas formation can occur within about 3 days
What effect does enviromental temp have on the rate of decomposition?
Low temps slow decomposition
Warm temps speed it up
At what temps is the rate of decomposition highest?
21-38ºC
What effect does intense heat have on the rate of decomposition and why?
Delays the start as intense heat denatures the enzymes involved in autolysis
What effect do injuries to the body have on the rate of decomposition and why?
Aids/speeds up decomposition as allows the entry of bacteria
