0 WHAT HAPPENS TO A BODY AFTER DEATH?

When I ask this question, I don't mean - like do they take pics of your body, then take it to the morgue... in a van... No, I'm also not asking whether it goes to some mystical place beyond. No.  What I want to know here is what happens to the body physically after it ceases to function and is declared dead.  The decomposition aspect of it.  What are the stages involved. 

A flower, a skull and an hourglass stand in for Life, Death and Time
in this 17th-century painting by Philippe de Champaigne

Stages
Five general stages are used to describe the process of decomposition: Fresh, Bloat, Active and Advanced Decay, and Dry/Remains. The general stages of decomposition are coupled with two stages of chemical decomposition: autolysis and putrefaction. These two stages contribute to the chemical process of decomposition, which breaks down the main components of the body.

Fresh
To begin with, when your heart stops beating, your body's cells and tissues stop receiving oxygen. Brain cells are the first to die -- usually within three to seven minutes.
(Bone and skin cells, though, will survive for several days.)


Since blood is no longer being pumped through the body it drains to the dependent portions of the body, under gravity, creating an overall bluish-purple discolouration termed livor mortis or, more commonly, lividity, (the darker the flesh - the longer the body has been dead).
Shortly after death, within three to six hours, the muscular tissues become rigid and incapable of contraction - stiffening of the muscles - which is known as rigor mortis.  From the moment of death, the body begins losing heat to the surrounding environment.  
Around 12 hours after death, the body will feel cool, and within 24 hours (depending on body fat and external temperatures), it will lose all internal heat in a process called  algor mortis. The muscle tissue begins to lose its stiffness after about 36 hours, and within about 72 hours of dying, the body's rigor mortis will subside.  

Once the heart stops, chemical changes occur within the body and result in changes in pH, causing cells to lose their structural integrity. The loss of cell structure brings about the release of cellular enzymes capable of initiating the breakdown of surrounding cells and tissues. This process is known as autolysis. Visible changes caused by decomposition are limited during the fresh stage, although autolysis may cause blisters to appear at the surface of the skin.

As the cells die, bacteria within the body begin breaking them down. Enzymes in the pancreas cause the organ to digest itself. The body soon takes on a gruesome appearance and smell. (As one forensic anthropoligist, Dr. Murray Marks described it - "It's not like garbage, it's not even like a dead animal - it's not like a mouse behind your wall that has died... It's like a pungent sweet smell - you'll never forget it"). 


Decomposing tissue emits a green substance, as well as gasses such as methane and hydrogen sulfide and ammonia.   This process of microbial proliferation within a body is referred to as putrefaction and leads to the second stage of decomposition, known as bloat. 


Insects and animals certainly take notice of all this. A human body provides sustenance and a great place for insects to lay eggs. A fly trying to find its way in this crazy, mixed-up world can eat well on a corpse, and then lay up to 300 eggs upon it that will hatch within a day.
Blowflies and flesh flies are the first carrion insects to arrive, and seek a suitable oviposition site.


Bloat
The bloat stage provides the first clear visual sign that microbial proliferation is underway. In this stage, anaerobic metabolism takes place, leading to the accumulation of gases, such as hydrogen sulphide, carbon dioxide, and methane. The accumulation of gases within the bodily cavity causes the distention of the abdomen and gives a cadaver its overall bloated appearance. The gases produced also cause natural liquids and liquefying tissues to become frothy. As the pressure of the gases within the body increases, fluids are forced to escape from natural orifices, such as the nose, mouth, and anus, and enter the surrounding environment. The build up of pressure may also cause rupturing of the skin.
Intestinal anaerobic bacteria transform haemoglobin into sulfhemoglobin and other coloured pigments. The associated gases which accumulate within the body at this time aid in the transport of sulfhemoglobin throughout the body via the circulatory and lymphatic systems, giving the body an overall marbled appearance.


If insects have access, maggots - extremely efficient and thorough flesh-eaters, hatch and begin to feed on the body’s tissues. Maggot activity, typically confined to natural orifices and masses under the skin, causes the skin to slip and hair to detach from the skin. Maggot feeding, and the accumulation of gases within the body, eventually leads to post-mortem skin ruptures which will then further allow purging of gases and fluids into the surrounding environment. Ruptures in the skin allow oxygen to re-enter the body and provide more surface area for the development of fly larvae and the activity of aerobic microorganisms.


Moving around as a social mass, maggots feed on decaying flesh and spread enzymes that help turn the body into delectable goo. The breathing mechanism of a maggot is located on the opposite end of its mouth, enabling it to simultaneously eat and breathe without interruption around the clock. While a first-stage larva is about 2 millimeters long, by the time it exits the third stage and leaves the body as a prepupa, it may be as large as 20 millimeters -- 10 times its initial length. Maggots can consume up to 60 percent of a human body in under seven days!  Also, maggots don't like sunlight - they leave the skin as an umbrella as they eat all of the interior organs away!

Active Decay

Active decay is characterized by the period of greatest mass loss. This loss occurs as a result of both the voracious feeding of maggots and the purging of decomposition fluids into the surrounding environment. The purged fluids accumulate around the body and create a cadaver decomposition island (CDI). Liquefaction of tissues and disintegration become apparent during this time and strong odours persist. The end of active decay is signaled by the migration of maggots away from the body to pupate.

The environment in which a dead body is placed also affects its rate of decay. For instance, bodies in water decompose twice as fast as those left unburied on land. Decomposition is slowest underground -- especially in clay or other solid substances that prevent air from reaching the body since most bacteria require oxygen to survive.


Advance Decay
Decomposition is largely inhibited during advanced decay due to the loss of readily available cadaveric material. Insect activity is also reduced during this stage. When the carcass is located on soil, the area surrounding it will show evidence of vegetation death.  The CDI surrounding the carcass will display an increase in soil carbon and nutrients, such as phosphorus, potassium, calcium, and magnesium; changes in pH; and a significant increase in soil nitrogen.


Dry/Remains
During the dry/remains stage, the resurgence of plant growth around the CDI may occur and is a sign that the nutrients present in the surrounding soil have not yet returned to their normal levels. All that remains of the cadaver at this stage is dry skin, cartilage, and bones, which will become dry and bleached if exposed to the elements. If all soft tissue is removed from the cadaver, it is referred to as completely skeletonized, but if only portions of the bones are exposed, it is referred to as partially skeletonized.

Resource(s):
howstuffworks.com
wikipedia
wikipedia