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Decomposition

Decomposition

The biological and chemical changes undergone by a body after death are known as decomposition. Decomposition is the continual process of gradual decay and disorganization of organic tissues and structures after death. Some tissues, such as bones, teeth, and hair, are more resistant to the action of microorganisms and other environmental factors and may last for centuries. Fossilized bones from animals and hominids, extinct millions of years ago, are studied today by paleontologists and anthropologists, thanks to such resilience.

Forensic medicine and forensic anthropology investigate the sequence and types of changes that affect decomposing bodies under different conditions and environments. A number of variables may affect both the rate and sequence of decomposition. Therefore, the estimation of time elapsed since death, known in forensics as the postmortem interval, takes into consideration the particular conditions associated with the decomposing body, such as temperature, level of humidity, and medium, such as exposure to preservatives, water, or soil.

For centuries, pigs were the animal model used to study both anatomy and the decomposition process due to their internal structural similarities to the human body. However, in 1980, the University of Tennessee at Knoxville began a research project on human decomposition with cadavers donated by the families of deceased persons or by the individuals who willed their bodies to science. In an area known as the Anthropological Research Facility, human bodies were laid to decompose in several different controlled conditions. These controlled experiments have significantly contributed to the better under-standing of human decomposition and to new levels of accuracy of forensic reconstruction techniques, such as the circumstances of death, time and cause of death , and determination of age, race, and gender. The data collected from several types of experiments and the measurements of each skeleton are recorded in a computer data bank named ForDisc (Forensic Discrimination).

A general description of postmortem changes due to decomposition basically includes two stages of autolysis, and four stages of putrefaction, besides some conservative phenomena such as saponification or adipocere , natural mummification, calcification, etc. However, these latter events only occur in specific conditions. Autolysis consists of the fast and intense spontaneous self-destruction of tissues by the body enzymes present in the cells, without any bacterial interference. Once cells stop receiving nutrients and oxygen via blood circulation, they start anaerobic (without oxygen) "breathing", breaking ATP (adenosine tri-phosphate) into ADP (adenosine di-phosphate) to obtain energy. Anaerobic respiration lasts for a few hours, until all ATP reserves are exhausted. The anaerobic respiration induces the accumulation of lactic acid in cell tissues that disrupts cell function. Enzymes then collapse the cell nucleus and cell breakdown (necrosis) occurs.

Tissues rich in blood vessels (more dependent on oxygen and energy) are the first ones to suffer autolysis, whereas those poorly irrigated or deprived from blood vessels, like the ocular corneas, are not immediately affected by decomposition. Putrefaction (or breakdown by microorganisms) follows autolysis. With the exception of fetuses and newly born babies, the main source of these microorganisms in corpses is the right part of the large intestines. Microorganisms then invade the abdominal cavity, the chest, head, and limbs. The first visible signs of such activity are the greenish abdominal stains, accompanied by the initial odors of rotting flesh. The stains gradually expand to other parts of the body (thorax, head, and limbs) and change from light to dark green, then beginning to blacken. In people who have drowned, the greenish coloration starts on the face, progresses toward the thoracic area, and then to other parts, due to the position that drowned bodies assume in water, which facilitates putrefaction of the upper respiratory pathways first. In newly born infants, putrefaction agents (bacteria, fungi, etc.) invade the body through all cavities, especially through the respiratory pathways. The greenish stains appear in newly born babies first on the face, neck, and chest due to bacterial activity in the upper and lower respiratory pathways, and because their intestines are sterile. This phase of decomposition is known as the chromatic period.

Bacterial action destroys the structure of cells and soft tissues, releasing in the process body fluids in internal cavities such as chest, abdomen, and oral tract. Anaerobic microorganisms produce methane, hydrogen sulphide, and other gases responsible for the increasing stench that surrounds rotting organic matter. As gases accumulate inside the body, it starts to swell, forcing more fluids from organs to internal cavities and blood to the periphery of the body. This phase of decomposition is called the gaseous period.

Subcutaneous (under the skin) blisters containing a mixture of plasma, hemoglobin , and gases appear and a marbled-like pattern spreads through the skin. The outer layers of the skin (epidermis) begin to detach from inner layers of the skin (dermis) as the gaseous period progresses. The subsequent phase involves the process of liquid putrefaction, in which the soft tissues are gradually dissolved. The body loses its shape as tissue mass decreases and the separation of skin layers is completed. During this liquefaction period, gases are released and a putrefied creamy substance covers the skeleton. The next phase is known as skeletonization, with the environmental elements (e.g., larvae, worms, and sometimes insects) separating the skeleton from ligaments, which causes the detachment of the skull , the mandible, and long bones, with bones eventually collapsing apart. Bones become increasingly fragile and lighter over the years, and acidic soils eventually dissolve them.

Adipocere (a waxy substance formed after death by fatty tissues) formation is not a universal phenomenon during decomposition. It is more common in remains of children, women, and overweight people, requiring both adipose (fatty) tissues and contact with humidity in the soil, or immersion in water, or the prevention of body water evaporation. Collective burial graves, were bodies are piled together, are also favorable to adipocere formation. Adipocere is very rare in remains of slim individuals because it results from the spontaneous chemical transformation of fatty tissues into a grayish-white waxy matter. Coroners have a special interest in adipocere because of its preservation properties of other tissues underneath. Adipocere-conserved body parts allow the performance of several forensic tests some months (and even years) after death. Examples are, the study of facial or neck lesions, toxicological tests, or the study of perforations caused by bullets.

Unborn fetuses that die between the sixth and the ninth months of pregnancy undergo a different process, known as maceration, due to prolonged exposure to the amniotic fluid. Fetal maceration external signs resemble in some ways those found in corpses immersed in water. However, the precise sequence of internal changes in fetal maceration is unique and offers three different well-defined phases or maceration degrees that allows the forensic determination of postmortem interval.

see also Adipocere; Autopsy; Bacterial biology; Body Farm; Crime scene reconstruction; Death, cause of; Drowning (signs of); Entomology; Exhumation; Immune system; Medical examiner; Mummies; Osteology and skeletal radiology; Toxicology.

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decomposition

decomposition
1. In switching theory, the realization of an n-variable switching function as a composition of functions, each of which has less than n variables. Like other minimizations, decomposition is facilitated by Karnaugh maps.

2. In programming, the analysis of a problem into simpler subproblems. See program decomposition, modular programming.

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decomposition

decomposition Natural degradation of organic matter into simpler substances, such as carbon dioxide and water. Organisms of decay are usually bacteria and fungi. Decomposition recycles nutrients by releasing them back into the ecosystem.

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decomposition

decomposition (dee-kom-pŏ-zish-ŏn) n. the temperature-dependent gradual disintegration of dead organic matter, usually foodstuffs or tissues, by the chemical action of bacteria and/or fungi.

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decomposition

decomposition (decay) The chemical breakdown of organic matter into its constituents by the action of decomposers.

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