State of decay
Although the body shortly after death appears fresh from the outside, the bacteria that before death were feeding on the contents of the intestine begin to digest the intestine itself. They eventually break out of the intestine and start digesting the surrounding internal organs. The body's own digestive enzymes (normally in the intestine) also spread through the body, contributing to its decomposition.
On an even smaller scale, enzymes inside individual cells are released when the cell dies. These enzymes break down the cell and its connections with other cells -to three weeks. It can take considerably longer at low temperatures.
1. Heart stops beating and/or lungs stop breathing.
2. Body cells no longer receive supplies of blood and oxygen.
Blood drains from capillaries in the upper surfaces and collects in the blood vessels in the lower surfaces.
Upper surfaces of the body become pale and the lower surfaces become dark.
3. Cells cease aerobic respiration, and are unable to generate the energy molecules needed to maintain normal muscle biochemistry.
Calcium ions leak into muscle cells preventing muscle relaxation.
Muscles stiffen and remain stiff (rigor mortis) until they begin to decompose.
4. Cells eventually die and the body loses its capacity to fight off bacteria.
5. The cells' own enzymes and bacterial activity cause the body to decompose - muscles lose their stiffness.
Timing?
Brain cells can die if deprived of oxygen for more than three minutes. Muscle cells live on for several hours. Bone and skin cells can stay alive for several days.
It takes around 12 hours for a human body to be cool to the touch and 24 hours to cool to the core.
Rigor mortis commences after three hours and lasts until 36 hours after death.
Rigor mortis refers to the state of a body after death, in which the muscles become stiff. It commences after around 3 hours, reaching maximum stiffness after 12 hours, and gradually dissipates until approximately 72 hours after death. Rigor mortis occurs due to changes in the physiology of muscles when aerobic respiration ceases.
Muscles are made up of two types of fibre. These fibres have connections between them that lock and unlock during muscle contraction and relaxation. These connections are controlled by a biochemical pathway within the cell, which is partially driven by the presence of calcium ions.
The concentration of calcium ions is higher in the fluid surrounding muscle cells than it is inside the cells, so calcium tends to diffuse into the cell. High calcium levels inside the cell drive the biochemical pathway in the direction that maintains muscle contraction. To relax, muscle cells must expel the calcium ions from the cell and this requires energy molecules to pump them across the cell membrane.
After a body has died, the chemical reaction producing these energy molecules is unable to proceed because of a lack of oxygen. The cells no longer have the energy to pump calcium out of the cell and so the calcium concentration rises, forcing the muscles to remain in a contracted state. This state of muscle stiffening is known as rigor mortis and it remains until the muscle proteins start to decompose.
Grave wax, or adipocere, is a crumbly white, waxy substance that accumulates on those parts of the body that contain fat - the cheeks, breasts, abdomen and buttocks. It is the product of a chemical reaction in which fats react with water and hydrogen in the presence of bacterial enzymes, breaking down into fatty acids and soaps. Adipocere is resistant to bacteria and can protect a corpse, slowing further decomposition. Adipocere starts to form within a month after death and has been recorded on bodies that have been exhumed after 100 years
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