rigor mortis

what is the normal range for human body temperature

36.2-37.6 degrees

what happens immediately after death

the body starts to cool due to the absence of heat producing chemical reactions

how long is the body temperature useful for in determining time of death

the first 24 hours

what type of curve does body cooling follow

the sigmoid curve

what is another name for environmental temperature

ambient temperature

what is assumed of the body when calculating the time of death and when might this not be the case

that the body was of a normal temperature at 37 degrees - if the person's suffering from fever or hypothermia

when using body temperature to determine the time of death what other factors needs to be recorded

body size, fat position, clothing, air movement, humidity, environmental air temperature, immersion in water, mode of death

what does rigor mortis mean

stiffness of death

what happens to the joints after death and after a period of time

they become fixed in a position that is dependant on body position at the time - after a period of time rigor mortis passes and the muscles are relaxed again

what is the sequence of the events of rigor mortis (5)

after death the muscle cells become starved of oxygen and oxygen dependant reactions stop, respiration in the cells become anaerobic and produce lactic acid, the pH of the cells falls which inhibits the enzymes and in turn anaerobic respiration, the ATP needed for muscle contraction is no longer produced and as a result bonds between muscle proteins become fixed, the process can no longer move over one another to shorten the muscle which fixes the muscle and joints

which muscles will stiffen and then pass through rigour more quickly

smaller ones

what factors can bring on and cause rigor to pass more quickly

an increased environmental temperature

what happens to cause rigor to pass

the muscles start to go through decomposition as lysosomes hydrolyse cells

how long is rigor mortis useful for in determining time of death

3 - 48 hours

how long does it take for bodies to have complete rigor mortis

6-9 hours

what happens immediately after death in decomposition

autolysis occurs as digestive enzymes from the digestive tract and lysosomes start to break down cells

what is the role of bacteria in the first stages of decomposition

putrefaction - bacteria from the digestive tract an gas exchange system rapidly invade the tissues and they release digestive enzymes, the lack of oxygen promotes the growth of anaerobic bacteria

what are the first signs of decomposition

a greenish discolouration appears on the skin of the abdomen due to anaerobic bacteria converting haemoglobin into sulfhaemoglobin and the discolouration spreads across the body darkening to reddish-green and then purple-black

what is the time frame for the discolouration

between 36-72 hours

what happens during and after the gas phase

bacteria produces gases in the tissues and intestine - hydrogen sulfide, methane, CO2, ammonia and hydrogen, the body becomes bloated and starts to smell and after further decomposition the gas escapes and the body deflates and fluid drains away causing the tissue to shrink and the body to dry

how long does it take for gas to be produced

usually after 7 days or within 72 hours if the temperature remains high like above 26 hours

what factors affect the rate of decomposition

ambient temperature, clothing, body injuries (aids entry of bacteria, intense heat (slows as enzymes denature)

why is the process of decomposition so useful in determining time of death

it follows a specific sequence

what is meant by the term entomology

the study of insects and their life cycles

what does a forensic entomologist need to collect once a body has been found

sample of insect and where it was found, maggot mass, air, body and ground temperature, information about the habitat, condition of the body, temperature history of habitat

how are the collected maggots used

the length of maggot is measured to determine age, live maggots are fed to allow to complete their development to adult to aid species identification and the timing of their pupation

what is the process of determining the time of death using forensic entomology

maggot length can be compared to growth graph to establish their age, the stage of maggot development can be linked in with the fly life cycle timings, this information helps work back to when the egg was laid but this is only reliable if the ambient temperature remains constant

why is looking at maggots an underestimate

there is no way of knowing when the fly found the body so the time is the minimum estimate

what factors can affect the estimation of time of death with forensic entomology

temperature, toxins - cocaine speeds up or heroin slows down maggot and pupal development

what factors determine which insects are on the body at a particular time

stage of decomposition of the body, presence of other insects - predators would be attracted

why is the colonisation of insects on a decomposing body considered to be a farm of succession

one group of organisms feed on the body, changing the conditions so that they become attractive to another group - species are replaced by others over a period of time but the first species may still be present so species richness increases

what other information can insects provide

if the body has been moved to another location as species will be different in different habitats

why is forensic entomology so useful in determining time of death

there is a predictable sequence of organisms that feed on a decomposing body, there is detailed knowledge about the life cycle timings for each species

what are two ways in which insects are attracted to a decomposing corpse

some of the insects feed off the decaying corpse, others are attracted as they feed on the insects around it

describe how insects succession on corpses

one group of organisms feed on a decomposing body causing the conditions to change in such a way that the body becomes attractive to another group of organisms, as the corpse continues to change it attracts different organisms that feed on it until only the skeleton remains

describe the contribution of bacteria and fungi in the decomposition of the body

bacteria from the gut quicky invade the tissue after death and other fungi and bacteria from surroundings colonise the corpse which contributes to the decay and changing conditions on the decomposing body

why is the body a great source of energy for decomposers

the organic carbohydrates, proteins, fats, nucleic acids are used as a food source which energy is released through aerobic and anaerobic respiration

what does this energy enable bacteria and fungi to do

grow and multiply rapidly to ensure more decomposition

how is decomposition linked into the carbon cycle

it sustains the carbon cycle as carbon dioxide is released into the atmosphere by the respiring decomposers and recycles it into a form that can be used in photosynthesis in plants to synthesise more organic molecules