Time of Death Flashcards
(51 cards)
What are the 5 ways to measure time of death?
- Rigor mortis
- Stage of succession
- Forensic entomology
- Body temperature
- Decomposition
Define “rigor mortis” 2
- Stiffening of muscles after death
- Joints and muscles became fixed in position i.e bent/flexed depending on body position at death
When does rigor mortis start?
4 hours
When have all the muscles contracted by?
12 hours
When does rigor mortis stop by?
After 24 hours
How does the muscle size effect rigor mortis?
Smaller muscles contract before larger ones
Why does rigor mortis occur? 7
- After death there is no oxygen so oxygen dependent reactions stop
- Respiration is anaerobic so lactic acid is produced
- Cell pH flls, denatures enzymes so anaerobic respiration stops
- ATP needed for muscle contraction not produced
- Bonds between myosin and actin in muscle cells are fixed
- Can’t move over each other to shorten muscle
- Fixes joints and muscles so body stiffens
What affects muscle contraction? 2
- Degree of muscle development
- Temperature
How does temperature affect muscle contraction? 2
- Higher temperatures means faster chemical reactions
- Faster rigor mortis
What is the time period for stage of succession?
Hours - months
How can stage of succession be used to find time of death? 2
- Species composition found on body changes over time
- Particular stage of succession shows time of death
What are the stages of succession from death to skeleton?
- Bacteria
- Flies and larvae
- Beetles
- Body dries out: flies leave, beetles remain as they can decompose dry tissue
- Minimal organisms as no tissues in skeleton
What are the external factors affecting stage of succession on a body? 2
- Location of body
- If body is sealed off
Why do all mammals produce heat? 2
- Because they are endotherms and warm blooded
- Heat is produced in metabolic reactions e.g respiration
What is the human core temperature?
37c
What happens to body temperature from TOD?
It falls until it reaches the surrounding temperature
Why does body temperature fall after TOD?
Metabolic heat producing reactions slow down and eventually stop
What rate does the human body cool at?
1.5-2 degrees c per hour
What assumption is made when using body temperature to calculate TOD?
The body is at a normal temperature at death but hypothermia/fever could affect this
List the environmental factors affecting cooling rate 7
- Body size
- Body position
- Clothing
- Air movement
- Surrounding temperature
- Humidity
- If body submerged in water
How does body size and body position affect cooling rate?
Exposed surface area is smaller/larger
How does clothing affect cooling rate?
Acts as an insulator trapping heat
How does air movement affect cooling rate?
Moving air speeds up heat loss
How does the body being submerged in water affect cooling rate?
Body submerged in water cools faster because water is a better conductor of heat
