Infection, Immunity & Forensics Flashcards
DETERMINING TIME OF DEATH
Factors used to determine the time of mammalian death?
- Extent of Decomposition
- Stage of Succession
- Forensic Etermology
- Body Temperature
- Degree of Muscle Contraction
Degree of Muscle Contraction is also known as Rigor Mortis
DETERMINING TIME OF DEATH
Body Temperature - Use to determine time of death?
Rate of Cooling-
Exothermic Metabolic reaction stops after death
Body begins to cool down to ambient temperature
Body Cooling follows a sigmoid (s-shaped) curve on a graph
Temperature can only be used to determine TOD 24 hours after death as it will eventually reach the same temperture as the surroundings.
DETERMINING TIME OF DEATH
Factors affecting the rate of cooling?
Slows Cooling:
* Body Size
* Body Position
* Clothing
* Humidity
Speeds Cooling:
* Air Movement
DETERMINING TIME OF DEATH
Rigor Mortis - The process?
Degree of Muscle Contraction
- Muscles become deprived of oxygen
- Anaerobic respiration occurs, causing build up of lactic acid in muscles
- PH decreases due to lactic acid - denatures enzymes and stops anaerobic respiration
- Without presence of ATP, actin and myosin in muscle fibres stick permanately together
- Muscles can no longer relax, so they contract causing the muscle and eventually body to stiffen.
Lactic Acid also causes ATP production to be inhibited by Enzymes
DETERMINING TIME OF DEATH
Rigor Mortis - Use to determine time of death?
After death = muscles begin to stiffen
* Starts - 2- 4 hours after death
* Full effect - 6 - 8 hours after death
* Passes - 36 - 48 hours after death
Only applicable after the first 36 hours - muscle stiffness wears off as muscle fibres breakdown.
Warmer Conditions = quicker process of Rigor Mortis
DETERMINING TIME OF DEATH
Stages of Decomposition
Initial Stages:
AUTOLYSIS OCCURS - enzymes break down the gut wall
Dying cells release enzymes which help break down tissues
LACK OF O2 IN TISSUES FAVOURS GROWTH OF ANAEROBIC BACTERIA - bacteria invades tissues and releases more enzymes.
DETERMINING TIME OF DEATH
Stages of Decomposition
After a few hours:
Cells and tissues are broken down by
- Bacteria (present before death)
- Enzymes
SKIN TURNS GREEN
DETERMINING TIME OF DEATH
Stages of Decomposition
Few Days - Weeks:
- Microorgansims decompose tissues and organs
- Gasses prdocued causing bloating
- Skin blisters and falls off
After few weeks:
* skin liquefys and seeps into area surrounding the body - bloating and deflation.
DETERMINING TIME OF DEATH
Stages of Decomposition
Few months - Centuries
Few months - years:
Skeleton remains
Decades - Centuries:
Skeleton Disintergrates - nothing left
DETERMINING TIME OF DEATH
Extent of Decomposition - Used to Determine time of death?
- Bodys in similar environmental areas show regular patterns of decay.
[ fresh — bloating — decaying — dry ]
Stages can be used to determine how long a body has been dead for
DETERMINING TIME OF DEATH
Factors affecting the extent of decomposition?
- mild heat
increases rate as enzyme activity increases - Intense heat
decreases rate as enzymes become deatured - Humidity
the more humid, the quicker the rate - Presence of wounds
Increases rate as bacteria are more easily able to enter the body
At extremely dry conditions - the process can stop altogether, eg: mummies
DETERMINING TIME OF DEATH
Stages of Successsion
- Anaerobic bacteria thrives
- Flies lay eggs on carcass
- Eggs hatch — maggots eat skin and tissue —-adult flies feed on liquidised parts.
- Beetles lay eggs, grub that hatches eats maggots
- Parasitic Wasps lay eggs in beetle and fly larvae
- Body dries out —- Cheese Coffin flies abundant (or species like)
- Dehydration, maggots can’t survive — beetles eat remaining muscles/ connecting tissues
- Mites and Moth larvae digest hair
DETERMINING TIME OF DEATH
Stage of Succession- Used to determine time of death?
- as body decays = species colonising the body will change [SUCCESSION IN SPECIES]
- analysis of community present can be used to determine time of death
DETERMINING TIME OF DEATH
Factors affecting Succession
- Season
- Weather
- Size
- Location of body
All influence the type and number of species present
DETERMINING TIME OF DEATH
Forensic Etermology - Used to determine time of death?
each species of insects has a specific life cycle
For Example:
Egg ( 1 day ) — Larva ( 9 days) — Pupa ( 6 -12 days) — ADULT FLY
Determining age of insects on corpse can be used to determine time of death
