6.1.1 - Determining The Time Of Death Flashcards
What Do Microorganisms Decompose?
Organic matter.
What Happens When Plants & Animals Die In Terms Of Microorganisms?
They secrete enzymes that decompose the dead organic matter into small molecules that they can respire
What Happens When The Microorganisms Respire The Small Molecules?
Methane and CO2 are released, recycling carbon back into the atmosphere.
What Is Forensics & What Does It Involve?
(2 Points)
~ The use of science in the investigation of criminal activities.
~ Involves the collection and analysis criminal evidence.
What Can The Time Of Death (TOD) Be Used For?
Provides information about the circumstances surrounding the death of the person.
In Order To Accurately Estimate TOD, What Factors Must Be Established?
(5 Points)
~ Body temperature.
~ Degree of muscle contraction.
~ Forensic entomology.
~ Extent of decomposition.
~ Stage of succession.
What Does Respiration & Other Metabolic Processes Produce In Living Organisms?
Heat
Why Is Heat Necessary For The Human Body?
Helps maintain body temperature.
What Is The Body’s Internal Temperature?
37°C.
At What Rate Does Body Temperature Decrease
After Death?
By 1.5 -> 2.0°C per hour.
What Is The Process Of Cooling The Body After Death Called?
Algor mortis.
Describe Body Temperature As A Method To Accurately Measure TOD
(4 Points)
~ Once a persons dies, metabolic reactions slow down and eventually stop.
~ Causing body temp to fall until it reaches the temperature of its surroundings, known as algor mortis.
~ Body temp decreases by 1.5 -> 2.0°C per hour, providing a way to determine the TOD.
~ Some factors can affect the cooling rate of a body.
What Factors Affect The Rate Of Body Heat Loss?
(3 Points)
~ Air temperature.
~ SA:V ratio.
~ Clothing.
What Happens Around 4-6 Hours After Death?
The muscles in the body start to contract and become stiff, this is known as rigor mortis.
What Is Rigor Mortis?
After death muscles in the body begin to contract and become stiff.
How Long Does It Take For Every Muscle In The Body To Contract After The TOD?
12 to 18 hours.
How Long Does It Take For Rigor Mortis To Wear Off After The TOD?
24 to 36 hours.
What Speeds Up The Rate Of Rigor Mortis?
Higher temperatures.
Describe Degree Of Muscle Contraction As A Method To Accurately Measure TOD
(5 Points)
~ Rigor mortis begins when the muscle cells become deprived of oxygen.
~ Respiration still takes place in the muscle cells, anaerobically as there is no oxygen this builds-up lactic acid in the muscle.
~ Accumulation of lactic acid decreases the pH in the muscle cells, denaturing the enzymes which produce ATP.
~ Without ATP, myosin heads cannot be released from the actin filaments, locking in the muscles in a contracted state.
~ Leading to stiffness.
Which Muscles Contract First & Last In Rigor Mortis & How Can This Help Determine The TOD?
(2 Points)
~ Smaller muscles in the head contract first, larger muscles in the lower body contract last.
~ This enables experts to determine TOD by the progress of rigorous mortis through the body.
What Is Rigor Mortis Affected By?
(2 Points)
~ Degree of muscle development.
~ Temperature of surroundings.
What Is Forensic Entomology?
The study of how quick a dead body is colonised by a variety of different insects.
Describe Forensic Entomology As A Method To Accurately Measure TOD
(2 Points)
~ Different insect species will colonise a body at different times after death. E.g. 1st is flies, then its beetles.
~ Insects can provide the stage of the lifecycle they are at. E.g. Blowfly larvae hatch after 24 hours, if larvae are present the TOD will be no longer than 24 hours.
What Conditions Affect The Progression Of Insect Lifecycles?
(4 Points)
~ Drugs that may be present in the body.
~ Humidity of surroundings.
~ Oxygen availability.
~ Temperature
What Happens Immediately After Death?
Bacteria and enzymes (Decomposers) begin to decompose the body via enzymes secreted from their cells.
Describe Extent Of Decomposition As A Method To Accurately Measure TOD
(5 Points)
~ Hour to a few days -> Cells and tissues are broken down by decomposers, skin begins to turn a greenish colour.
~ Few days to a few weeks -> Microorganisms break down decompose tissues and organs, produces gases such as methane leading to bloating and the skin begins to blister and fall off.
~ A few weeks -> Tissues begin to liquefy and seep out into areas around the body.
~ Few months to a few years -> Only a skeleton remains.
~ Decades to centuries -> Skeleton begins to disintegrate until there’s nothing left of the body.
What Factors Affect The Rate Of Decomposition?
(2 Points)
~ Temperature.
~ Oxygen availability, affecting aerobic microorganisms dependent on oxygen.
What Is Succession?
Change in types of organisms found in a habitat over time.
Describe Stages Of Succession Above Ground As A Method To Accurately Measure TOD
(6 Points)
~ Bacteria will be found in and on the dead body immediately after TOD.
~ As bacteria decompose tissues, conditions in a dead body become favourable for flies and their larvae.
~ As more soft tissue is consumed by the larvae, it creates favourable conditions for beetles.
~ As the tissues dry out flies will leave as it becomes less favourable for them.
~ Beetles remain as they can decompose dry tissue.
~ When no tissue remains conditions are no longer favourable for most organisms so they leave.
What Factors Affect The Stage Of Succession Of A Dead Body?
(2 Points)
~ Where the body is located, above or below ground, under water or sealed in a coffin.
~ This affects the accessibility to insects and availability of oxygen.
