Topic 6 Flashcards
What decomposes organic matter?
Microorganisms
What cycle are microorganisms an important part of?
Carbon cycle
Give examples of microorganisms
Fungi and bacteria
How do microorganisms decompose organic matter?
Microorganisms in and on them secrete enzymes that decompose the dead organic matter into small molecules that they can respire.
What is produced when microorganism respire?
Methane and CO2 which recycles carbon back into the atmosphere.
What are the 5 factors needed to work out the time of death of a body?
Body temperature Degree of muscle contraction Forensic Entomology Extent of decomposition Stage of Succession
How does looking at body temp help work out time of death?
1) All mammals produce heat from metabolic reactions like respiration
2) From the TOD metabolic reactions slow down and eventually stop, causing body temp to fall until it equals the temp of its surroundings - process called algor mortis
What is algor mortis?
the second stage of death, is the change in body temperature post mortem, until the ambient temperature is matched.
What is the human core body temperature?
36.2 - 37.6
How is core body temp measured?
Via the rectum or through an abdominal stab.
A long thermometer is needed as an ordinary thermometer is to short and has too small a temp range.
An electric thermometer can also be used
Describe the normal curve a cooling body will produce
Sigmoid curve
- Initial temp plateau normally lasts between 30 and 60 mins
- Decreases then plateaus
What factors will affect post-mortem cooling?
Body size Body position Clothing Air movement Humidity Temp of surroundings
At what rate does a human body cool at?
1.5 - 2 per hour
What is rigor mortis?
About 4-6 hours after death the muscles in a dead body start to contract and become stuff
What determines the position (bent or straight) of the joints during rigor mortis?
Body position at TOD
Describe the process of rigor mortis.
1) Muscle cells become deprived of oxygen and oxygen dependant reactions stop.
2) Anaerobic respiration takes place in the muscle cells which causes a build up of lactic acid in the muscle
3) The pH of the cells decreases due to lactic acid, inhibiting enzymes that produce ATP
4) No ATP means bonds between the myosin and actin in the muscle cells become fixed and stiffen
5) The proteins can no longer move over one another to shorten the muscle, fixing the muscle and joints
What muscles contract first?
Smaller muscles in the head
What muscles contract last?
Larger muscles in the lower body
What factors affect rigor mortis?
Degree of muscle development
Temperature (high temp means rigor mortis sets in quicker but lasts for a shorter period)
If the person has been physically active before death
Why does a higher temp mean rigor mortis occurs quicker?
Chemical reactions in the body are faster
What is forensic entomology?
When somebody dies the body is quickly colonised by a variety of different insects, the study of this is forensic entomology.
How can forensic entomology be used to estimate TOD?
By identifying the type of insect present
- flies are often first insects to appear, usually a few hours after death
- Other insects such as beetles, colonise at later stage
Identifying the stage of life cycle the insect is in
- Blowfly larvae hatch 24 hours after they’re laid. If only blowfly larvae eggs were found, TOD was less than 24 hours previous
What affects the insect’s life cycle?
Drugs
Humidity
Oxygen
Temperature (high temp = faster metabolic reactions = shorter life cycle)
What happens if the stage of development of the insect is unclear?
Its allowed to mature which gives a date of pupation. If normal length of time for an egg to develop and pupate is subtracted from date of pupation, its possible to work out when the eggs where laid.