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Bio 6: Infection, Immunity and Forensics > Time of Death > Flashcards

Time of Death Flashcards

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1
Q

What are the 5 ways to measure time of death?

A
  • Rigor mortis
  • Stage of succession
  • Forensic entomology
  • Body temperature
  • Decomposition
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2
Q

Define “rigor mortis” 2

A
  • Stiffening of muscles after death

- Joints and muscles became fixed in position i.e bent/flexed depending on body position at death

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3
Q

When does rigor mortis start?

A

4 hours

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4
Q

When have all the muscles contracted by?

A

12 hours

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5
Q

When does rigor mortis stop by?

A

After 24 hours

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6
Q

How does the muscle size effect rigor mortis?

A

Smaller muscles contract before larger ones

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7
Q

Why does rigor mortis occur? 7

A
  • 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
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8
Q

What affects muscle contraction? 2

A
  • Degree of muscle development

- Temperature

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9
Q

How does temperature affect muscle contraction? 2

A
  • Higher temperatures means faster chemical reactions

- Faster rigor mortis

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10
Q

What is the time period for stage of succession?

A

Hours - months

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11
Q

How can stage of succession be used to find time of death? 2

A
  • Species composition found on body changes over time

- Particular stage of succession shows time of death

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12
Q

What are the stages of succession from death to skeleton?

A
  • 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
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13
Q

What are the external factors affecting stage of succession on a body? 2

A
  • Location of body

- If body is sealed off

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14
Q

Why do all mammals produce heat? 2

A
  • Because they are endotherms and warm blooded

- Heat is produced in metabolic reactions e.g respiration

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15
Q

What is the human core temperature?

A

37c

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16
Q

What happens to body temperature from TOD?

A

It falls until it reaches the surrounding temperature

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17
Q

Why does body temperature fall after TOD?

A

Metabolic heat producing reactions slow down and eventually stop

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18
Q

What rate does the human body cool at?

A

1.5-2 degrees c per hour

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19
Q

What assumption is made when using body temperature to calculate TOD?

A

The body is at a normal temperature at death but hypothermia/fever could affect this

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20
Q

List the environmental factors affecting cooling rate 7

A
  • Body size
  • Body position
  • Clothing
  • Air movement
  • Surrounding temperature
  • Humidity
  • If body submerged in water
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21
Q

How does body size and body position affect cooling rate?

A

Exposed surface area is smaller/larger

22
Q

How does clothing affect cooling rate?

A

Acts as an insulator trapping heat

23
Q

How does air movement affect cooling rate?

A

Moving air speeds up heat loss

24
Q

How does the body being submerged in water affect cooling rate?

A

Body submerged in water cools faster because water is a better conductor of heat

25
Q

Define “forensic entomology”

A

Study of insects

26
Q

What is the time period for forensic entomology?

A

Days - months

27
Q

How can species of insect be used to determine TOD?

A

Species of insect on body changes over time

28
Q

What two types of forensic entomology be used to determine TOD? 2

A
  • Species of insect

- Life cycle of insect

29
Q

How can life cycle of insect be used to determine TOD?

A

Stage of life cycle changes over time

30
Q

How does type of insect change over time?

A

Flies within hours to beetles colonising at a later change

31
Q

How does life cycle of a fly change over time?

A

Egg to small larvae to large larvae to pupae

32
Q

What type of insect is used to observe life cycle to determine TOD?

A

Fly

33
Q

When do blowfly larvae hatch?

A

After 24 hours

34
Q

What external factors affect life cycle of an insect? 4

A
  • Drugs
  • Humidity
  • Temperature
  • Oxygen levels
35
Q

How does temperature affect life cycle of an insect?

A
  • Higher temperatures mean higher metabolic rate

- Shorter life cycle

36
Q

Define “decomposition”

A

Tissues breaking down after death due to enzyme action

37
Q

Why does decomposition occur?

A
  • Autolysis occurs at death - body’s own enzymes break down cells
  • Bacteria invade tissues and release gases involved in decomposition
38
Q

What type of bacteria do the most decomposition and why?

A

Anaerobic bacteria - loss of oxygen in tissues at death favours its growth

39
Q

Why do bacteria invade the body?

A

Organic carbs, proteins, fats and nucleic acids in body are a food source

40
Q

What are the stages of decomposition? 4

A
  • Greenish skin discolouration
  • Production of gases
  • Bloating
  • Tissue liquefaction
41
Q

When does greenish skin discolouration occur?

A

Hours to a few days

42
Q

When does production of gases occur?

A

A few days to a few weeks

43
Q

Why does the production of gases occur?

A

Microorganisms decompose tissues and organs

44
Q

Why does bloating occur?

A

Production of gases produced by microorganisms decomposing tissues and organisms causes body to smell and bloat

45
Q

When does tissue liquefaction occur?

A

After a few weeks

46
Q

What happens in tissue liquefaction ?

A
  • Tissues further decompose
  • Gas is released
  • Body deflates
  • Tissues begin to liquefy and seep out around body
47
Q

How long does it take for the body to fully decompose into a skeleton?

A

Few months to a few years

48
Q

What environmental conditions affect decomposition rate? 3

A
  • Temperature
  • Oxygen availability
  • Bodily injuries
49
Q

How does a low temperature affect rate of decomposition?

A

Decreases rates of reactions and so decreases rate of decomposition

50
Q

How does a high temperature affect rate of decomposition?

A

Denatures autolysis enzymes so delays start of decomposition

51
Q

How do injuries affect rate of decomposition?

A

Allows increased entry of bacteria aiding decomposition

Bio 6: Infection, Immunity and Forensics (11 decks)

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