Biology__Topic 6__T6L4 Flashcards
What happens to a person’s body when they die? What can these be used for?
> A series of physical and chemical changes start to take place in their body
These can be used to estimate time of death.
What can be used to estimate time of death?
> Temperature of the body,
Degree of rigor mortis
State of decomposition
Entomological (insect) evidence
D E S T iny
How does human body temperature change after death? Why?
> Body cools due to the absence of heat-producing chemical reactions
Useful for estimating time of death during the first 24 hours post-mortem
The cooling of the body follows a sigmoid curve
What conditions may result in body temperature being an unreliable indicator of time of death?
> If a person has a fever or is suffering from hypothermia…
their body temperature at the point of death will be elevated or depressed.
What factors effect poste mortem cooling?
> body size - small - small SA/V ratio, less heat loss
body position - Spread - more SA exposed - more heat loss
clothing - insulation - less heat loss
air movement - lots of movement - higher temperature gradient - more heat loss.
humidity - Higher humidity - Slow heat loss
temperature of surroundings - High temp. - slow heat loss
immersed in water - water’s a better heat conductor than air - cools more rapidly
What is rigor mortis?
> Muscles totally relax and then stiffen
Joints become fixed.
Why does rigor mortis occur?
> After death, muscle cells become starved of oxygen and oxygen-dependent reactions stop.
Respiration in the cells becomes anaerobic and produces lactic acid.
pH of the cells falls, inhibiting enzymes and thus inhibiting anaerobic respiration.
The ATP needed for muscle contraction is no longer produced. As a result, bonds between the muscle proteins become fixed.
The proteins can no longer move over one another to shorten the muscle, fixing the muscle and joints.
At what time does rigor mortis complete?
> six to nine hours after death
Time of death related to stiffness and temperature of body
Warm, Not stiff - 36-48 hours
Describe process of decomposition after death
> Enzyme action breaks down tissues.
Autolysis occurs first. (This is when the body’s own enzymes, from the digestive tract and from lysosomes, break down cells.)
Bacteria from the gut and gaseous exchange system invade tissues after death, releasing enzymes –> decomposition
Loss of O2 favours anaerobic bacteria growth
What are the signs of decomposition? When do they occur?
- Greenish discolouration of skin of lower abdomen. This spreads across the body, darkening to reddish green then a purple black colour. (36-72h)
- Body bloats and smells due to gases produced by bacteria. (A week, but largely depends on temperature)
- As tissues further decompose, gas is released (body deflates).
How does environmental temperature effect rate of decomposition?
> Low temperatures slow down decomposition
> Rate is highest between 21 and 38C
Intense heat denatures the enzymes of autolysis, delaying decay
How are insects used to estimate time of death?
> The temperature of the air, ground, body and ‘maggot mass’ are measured…
so that the rate of maggot development can be determined
Live maggots are fed on meat, allowing them to complete their development, allowing species identification and to establish when they pupate.
Thus the time the eggs were laid can be estimated
Describe succession on corpses
> As one group of organisms (pioneer species) feeds on a decomposing body,
Conditions change in such a way that it becomes attractive to another group of organisms. > (As the corpse changes, it attracts different organisms that feed on it until only the skeleton remains)
How may temperature affect the process of succession on a human body?
> Higher temperature,
More kinetic energy,
Faster rate of reaction (more successful collisions),
Decomposers break down tissues faster,
Conditions change faster,
faster succession
