Determining the time of death Flashcards
Describe body temperature
Normal range is 36.2-37.6C
Used up to 24hrs after death
Measured via the rectum or abdominal stab into the liver
Cooling of the body follows a sigmoid curve
Factors affect accuracy:
Surface area, temperature, clothing, size and air movement
Describe rigor mortis
After death muscles usually totally relax and then stiffen
Joints become fixed during RM and position depends on body position at time of death
Small muscles go first
Hot temp means RM sets in quicker and shorter period
Describe the chemistry of rigor mortis
Muscles become starved of oxygen and respiration becomes anaerobic
Lactic acid denatures respiratory enzymes so no ATP is produced
no ATP to pump calcium out of sarcomere so binding sites remain exposed and cross bridges form
no ATP to break cross bridges that form in muscle contraction
Describe the first sign of decomposition
Putrefaction: greenish discolouration of skin of lower abdomen due to autolysis (tissue brokedn down by enzymes)
36-71 hours
Describe the second sign of decomposition
Discolouration spreads from redish green to purple
Gas or liquid blisters appear on skin due to build up of respiration gases from bacteria, corpse swells in a week
Describe the third sign of decomposition
Gas released and body deflated, fluid from 1st sign drains away, soft tissue shrinks
Factors: temp, injuries, location
Why would a well heated room speed up decomposition?
enzymes have more kinetic energy so more enzyme-substrate complexes formed
Bacteria multiply and more rapidly
Why would intense heat slow down decomposition?
Enzymes denature so bonds between R groups broken
Enzymes lose their specific shape so active site changes shape
What to look for to estimate time of death?
Length of maggot
Time taken to pupate
Temperature and species present
What is a maggot
Soft bodied legless larva found in decaying matter
Define forensic entomology
Use of insects that inhabit decomposing remains to solve crime
How do you measure the age of a maggot
Find length of maggot and temperature
Draw lines from temp to length
Describe estimating time of death based on egg hatching
If development is unclear, its allowed to pupate
Subtract hatching time normally from date of pupation
May be an underestimate as theres no knowing of how long it took for flies to find the body and lay eggs
Describe succession on a corpse
One species feed on decomposing body changing conditions to make it suitable for another species
Produces competition
Eggs laid in wounds or opening to the body
Species used to estimate time since death
