Topic 6: Estimating time of death II (decomposition)

What is decomposition?

The breakdown of dead organic matter.

What action results in the breakdown of dead organic matter?

The action of enzymes released mainly by microbes (decomposers)

What are optimal conditions for decomposition to occur?

• Injuries on the body

• Warm ambient temperatures

• Aerobic conditions

• Moisture

What does the first stage of decomposition involve?

Autolysis

What does autolysis mean?

Auto- By itself, Lysis- splits/breaks

What happens in the body during autolysis?

The cell is broken down by its own enzymes (commonly found in the lysosome).

Soon after autolysis, what will take over decomposition?

Bacteria

Where are the first sources of bacteria in the body?

Guts, skin and respiratory tract (which all already contain bacteria during life)

What allows the bacteria to multiply rapidly in the body after death?

The fact that the immune system can no longer keep the bacteria in check

What do the bacteria do in the body to attain food sources?

They break down organic molecules in body tissues.

After internal bacteria contributes to the body decomposition, what will enter the body and also contribute to decomposition?

External bacteria and fungi

What about decomposers give rise to a wide range of products?

The metabolism of decomposers which involves many different chemical reactions.

What type of products from the metabolism of decomposers gives arise to discolouration in the skin?

Products which are coloured.

Some products from the metabolism of the decomposers are gases, which gases are produced?

• Hydrogen sulphide

• Methane

• Carbon dioxide

• Ammonia

What do these gases cause the body to do?

• Smell

• Bloated

What is the wet phase of decomposition of decomposition known as?

Putrefaction

What happens to the fluid over time during decomposition?

The fluid drains away and the body becomes dry

What happens to the rate of decomposition as the body dries?

The rate of decomposition decreases

Are the decomposers active in a dead body most likely to be aerobic or anaerobic organisms?

Most likely anaerobic, as there is not enough oxygen inside the body as blood can no longer circulate, so now only diffusion on oxygen takes place, diffusion alone is not fast enough as in multicellular organisms, diffusion by itself is too slow

What is the affect of warm ambient temperature on the rate of decomposition?

INCREASE- as there is higher kinetic energy → this means there will be more frequent successful collisions between the substrate and enzymes as well as between reactant molecules → so more enzyme-substrate complexes are formed → decomposers have a higher metabolic rate

What is the affect of injuries to the body surface on the rate of decomposition?

INCREASE- microbes can enter the body more readily as there are more openings (the skin acts as a barrier against the entry of microbes into your body)

What is the affect of exposure to very high temperatures on the rate of decomposition?

DECREASE- denatures enzymes (both from own body and decomposers) → kills decomposers

What is the affect of very cold ambient temperature on the rate of decomposition?

DECREASE- very low kinetic energy → less frequent collisions between enzymes and substrates as well reactant molecules → less enzyme-substrate complexes formed → decreases metabolic rate + fluids frozen → less moisture availability

What is the affect of barrier preventing outside organism from accessing the body on the rate of decomposition?

DECREASE- less entry points to the body → less microbes can decompose the body

After the first week of death, what are the changes that occur in the body?

• Autolysis

• Temperature falls

• Rigor mortis

• Bloating