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.
What is succession of a body?
The types of organisms found in a dead body change over time, going through a number of stages
What will happen if a dead body is left to decompose above ground?
1) Immediately after TOD the conditions are most favourable for bacteria.
2) As bacteria decompose tissues, conditions in a dead body become favourable for flies and larvae
3) When fly larvae feed on a dead body they make conditions favourable for beetles, so beetles move in
4) As body dries out conditions become less favourable for flies, so they leave. Beetles remain as they decompose dry tissue
5) When no tissue remain, conditions are no longer favourable for most organisms
What is the difference between plant succession and body succession?
Early insects remain on the body as other insects colonise it.
What affects the stages of succession?
Location of the body (above ground, underground, in water)
Where are eggs usually laid?
In wounds or at openings of the body
When is a post-mortem performed?
If there is a sudden or unexpected death or if cause of death is unknown
How is a post-mortem performed?
1) External examination
2) Internal examination
- incision down front of body
- organs taken out for detailed examination
3) Blood and tissue samples may be taken and tested for toxins, infections or tumours
4) Contents of stomach may be analysed
What is lysis?
The disintegration of a cell by rupture of the cell wall or membrane.
What is an antigen?
A toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies.
What is an antibody?
An antibody, also known as an immunoglobulin, is a large, Y-shaped protein produced mainly by plasma cells that is used by the immune system to identify and neutralize pathogens such as bacteria and viruses.
What is an immunoglobulin?
Glycoprotein molecules produced by plasma cells (white blood cells). They act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses and aiding in their destruction.
What is a lysozyme?
An enzyme that kills bacteria by breaking down their cell walls.
What is phagocytosis?
The ingestion of bacteria or other material by phagocytes and amoeboid protozoans.
