PMI estimation in the late postmortem period. Flashcards
What are the five stages of decomposition?
- Fresh stage
- Bloat stage
- Active decay
- Advanced decay
- Skeletonisation.
What is the greenish discolouration of the skin called in the boat stage?
sulfhemoglobin
Briefly talk about each stage of human decomposition.
- Fresh stage: all the mortis occur.
- Bloat: gases build up in the lower abdomen and they are released, attracting flies. Bacterial putrefaction occurs and skin sloughing occurs.
- Active decay: insect activity increases and gases continue to be released.
- Advanced decay: flies and bacterial action are reduced, and the drying out of remains takes place.
- Skeletonisation: rate of decomposition slows down and gradual exposure of bones.
What is disarticulation?
-All limbs from the body have been disconnected.
Define the rate of decomposition.
- The speed at which a body transforms from a fresh whole body to complete skeltonization.
What two categories influence the rate of decomposition?
- Intrinsic factors: body size, clothing, disease, drugs.
- Extrinsic factors: temperature, weather, insects.
What is the relationship with the rate of decomposition and the temperature?
- Ambient temperature as the greatest effect on the rate of decay.
- Decay occurs in warm, damp environments.
- Main factor for decomposition.
- High temperature results in a higher insect activity and a low temperature results in a slowed insect activity.
What methods can be used to help establish the PMI?
- Entomology
- Botany
- Geology
- Volatile organic compounds (VOCs)
- Bone diagenesis and biochemistry.
What animal can be used to detects VOCs and bodies/ graves?
- Detection dogs
How are insects/ blowflies attracted to corpses?
- They are attracted by odours and volatile organic compounds.
- Maggots aid in physical construction of the human body as they consume the tissue.
What is the effect of moisture, humidity and rainfall in decomposition?
- For decomposition to progress it requires moisture and humidity.
- Decomposition will not progress or continue if the corpse is in a dry environment.
- Water/ rainfall can help speed up the process as it can liquefy the body.
What is the effect of sun and shade in regards of decomposition?
- Sun can speed up the progress of decomposition and this is because it warms up the remains and promotes bacterial decay.
- Insects will lay their eggs underneath the skin as if they are in direct sunlight, they will be destroyed due to the UV exposure.
When a body is buried, what promotes decomposition?
- Aerated soils.
- Coarse texture
- Free draining soils
- Acidic sands and gravel
- Sites that have manure
When a body is buried, what reduces the rate of decomposition?
- Poorly drained soil, moisture retention.
- Clay-based soils
- Poor aeration- roots deprived of oxygen.
- Adipocere formation and preservation of soft tissues.
What is adipocere formation?
- It is a waxy/ greasy product which is formed during the process of decomposition.
- Occurs through the process of hydrogenation and and hydrolysis of tissue fats.
What is the effect on decomposition with burial depth?
- When a body has been buried, the rate of decomposition decreases and this is because it takes longer to process due to being at deeper depths.
- This is due to the temperature being lower and its harder for insects to have access to the body.
When a body has been buried, what is the rate of decomposition reduced by?
- 4x slower
What is the relationship between decomposition and coffins?
- The rate of decomposition is reduced and this is because a coffin acts as a physical barrier.
- It is harder for insects to get to the body.
- If a iron coffin is used, it delays the onset of putrefaction by decades and soft tissues are still present.
What is the relationship between decomposition and water submersion?
- The body will undergo a differentiation of decomposition and this is because the rate of decomposition of the part of the body that is submerged in water will be different to the rate of decomposition of the parts of the body that are not submerged in water.
- When a body is submerged in water, the rate of decomposition reduces by half.
- Temperature is constant, but cooler than air.
What factors affect the rate of decomposition when a body is submerged in water?
- Mechanical destruction due to tides and waves.
- Chemical composition such as pH.
- Marine and freshwater scavengers contribute to the destruction of the body.
What is the relationship between decomposition and a body hanging from the ground?
- The rate of decomposition is slow compared to a body that is lying on the ground.
- This is because it is harder for insects and scavengers to access the body and all bodily fluids will drain away.
What is bone diagenesis?
- It is defined as the postmortem alterations in the physical, chemical and microstructure composition of bone following its decomposition in the environment.
- Bone degradation
What does desiccation mean?
- It means the removal of moisture from something.
- Browning of the skin.
What does Tache noir mean?
Drying of the eyes
Describe decomposition and body size.
- A small body (small SA:VR) = mummification.
- A large body (large SA:VR) faster decomposition.
What effect does clothing have on the rate of decomposition?
- Can reduce the rate of decomposition.
- Prevents insects accessing the body.
- Clothing can act as insulation and can maintain/ increase temperatures.
What drug slows down the rate of decomposition?
- Morphine
What drug can speed up the rate of decomposition?
- Cocaine can speed up the actions of insects.
What is TBS and what does it mean?
- The total body score.
- It is a visual scoring method to scale the succession of decomposition stages.
What does ADD stand for?
- Accumulated degree-days.
What is the min and ax score of TBS?
- Min score = 3, fresh
- Max score= 35, skeltonised
- Can be subjective.
What is accumulated degree days?
- A tool used to estimate PMI whilst taking into the account the temperature.
