Rigor mortis and decomposition

Changes

Soon as a person dies- series of changes take place
Changes- specific order and so can estimate time of death

Body temp

Ranges from 36.2-37.6 oC
Dies- body cools- absence of heat producing chemical reactions
Estimate time of death during the first 24 hours

Measure

Core body temp- large thermometer- rectum or through an abdominal stab
Electronic temp probe- can also be used
Cooling of the body follows a sigmoidal curve- initial temp plateau lasts between 30-60 mins
- over linear part of the curve temp decline per hour is used for estimating time of death

Cooling curve

Assume that the persons body temp-normal at 37 oC at time of death
May not be the case if a person has a fever or hypothermia

Many factors can effect the post morgen cooling

Body size
Body position
Clothing
Air movement
Humidity
Temperature of surroundings

Body temp and factors

Body size- cools slower with a larger mass
Body position- compact posture slower cooling
Clothing-more insulation, less heat loss
Air movement- cooling slower, less air movement
Humidity- high humidity- slower rate of cooling
Temp of surroundings- cooling occurs slower in warmer surroundings

Rigor mortis

After death- muscles usually relax then stiffen
Stiffening - rigor mortis (stiffness of death)
Joints become fixed and position (bent or straight) depends on body position at time of death
Further time- rigor mortis passes and muscles relax

Process

1) after death muscles become starved of oxygen and oxygen dependent reactions stop
2) respiration- cells- becomes anaerobic and produces lactic acid
3)pH of cells fall- inhibit enzymes and anaerobic respiration
4) ATP- needed for muscle contraction- no longer produced- bonds between the muscle protein is fixed
5) proteins can no longer move over one another to shorten the muscle ; fixing the muscle and joints

Time

Smaller muscles-stiffen before larger muscles
Rigor mortis- passes off as muscle tissue breaks down- same order as they develop
Most 6-9 hours after death (complete RM)
Environmental temp is high - RM sets in quicker and lasts for shorter periods of time or if they have been physically active before death

Warm and not stiff

Less than 3 hours

Warm and is stiff

3-8 hours since death

Cold and is stiff

8- 36 hours

Cold and not

More than 36-48 hours

Decomposition

After death tissue breaks down due to enzyme action
1st take- autolysis- bodies own enzymes (digestive tract and lysosomes) break down cells
Bacteria from gut and gas exchange system invade tissues after death, releasing enzymes resulting in decomposition
Loss of O2 in tissue favours growth- anaerobic bacteria

Signs of decomposition

1) putrefaction- greenish discolouration of the skin on the lower abdomen
Due to formation-sulfhaemoglobin- blood
2) spreads to the rest of the body- darken to reddish- green -> purple- black
3) gas or liquid blisters may appear on the skin-> bacteria -> gases (hydrogen sulphide, methane, CO2, ammonia and H2 form -> intestines and tissue-> smell and become bloated
4) further decomposition- gas released and body deflates
5) fluid associated with putrefaction drains away- soft tissue shrink and the decay rate (dry body) reduces

Time taken

Average conditions in a temperate climate-> discolouration of abdominal wall-> 36-72 hours after death
Gas formation- roughly a week
Temp determine rate- remains above 26 C- gas forms may occur within 3 days

Environmental temp

Major influence on rate of decomposition
Low temp- slow rate, warm temp- speed up
Rate highest between 21 and 38 oC
Intense heat- denatures enzyme involved in autolysis- delay start of decomposition
Injuries- entry of bacteria- aid decomposition