Time of Death Flashcards
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
Define “forensic entomology”
Study of insects
What is the time period for forensic entomology?
Days - months
How can species of insect be used to determine TOD?
Species of insect on body changes over time
What two types of forensic entomology be used to determine TOD? 2
- Species of insect
- Life cycle of insect
How can life cycle of insect be used to determine TOD?
Stage of life cycle changes over time
How does type of insect change over time?
Flies within hours to beetles colonising at a later change
How does life cycle of a fly change over time?
Egg to small larvae to large larvae to pupae
What type of insect is used to observe life cycle to determine TOD?
Fly
When do blowfly larvae hatch?
After 24 hours
What external factors affect life cycle of an insect? 4
- Drugs
- Humidity
- Temperature
- Oxygen levels
How does temperature affect life cycle of an insect?
- Higher temperatures mean higher metabolic rate
- Shorter life cycle
Define “decomposition”
Tissues breaking down after death due to enzyme action
Why does decomposition occur?
- Autolysis occurs at death - body’s own enzymes break down cells
- Bacteria invade tissues and release gases involved in decomposition
What type of bacteria do the most decomposition and why?
Anaerobic bacteria - loss of oxygen in tissues at death favours its growth
Why do bacteria invade the body?
Organic carbs, proteins, fats and nucleic acids in body are a food source
What are the stages of decomposition? 4
- Greenish skin discolouration
- Production of gases
- Bloating
- Tissue liquefaction
When does greenish skin discolouration occur?
Hours to a few days
When does production of gases occur?
A few days to a few weeks
Why does the production of gases occur?
Microorganisms decompose tissues and organs
Why does bloating occur?
Production of gases produced by microorganisms decomposing tissues and organisms causes body to smell and bloat
When does tissue liquefaction occur?
After a few weeks
What happens in tissue liquefaction ?
- Tissues further decompose
- Gas is released
- Body deflates
- Tissues begin to liquefy and seep out around body
How long does it take for the body to fully decompose into a skeleton?
Few months to a few years
What environmental conditions affect decomposition rate? 3
- Temperature
- Oxygen availability
- Bodily injuries
How does a low temperature affect rate of decomposition?
Decreases rates of reactions and so decreases rate of decomposition
How does a high temperature affect rate of decomposition?
Denatures autolysis enzymes so delays start of decomposition
How do injuries affect rate of decomposition?
Allows increased entry of bacteria aiding decomposition
