Decomposition and postmortem soft tissue changes

https://www.sciencedirect.com/topics/medicine-and-dentistry/algor-mortis#:~:text=The%20rate%20at%20which%20this,during%20the%20first%2012%20hours.

from 2014 book or article

5.2 Decomposition and postmortem soft tissue changes

The soft tissues of the body are the first to become modified after
death. Early visible postmortem changes to the soft tissues include
algor mortis, livor mortis, and rigor mortis, stages which are
typically assessed by investigators and the medical examiner at
autopsy. Algor mortis is the cooling of the body after death (Knight,
2002). During life, the body maintains a temperature of approximately
98.6°F, which is an optimum operating temperature for many of the
body's chemical reactions. After death, the body no longer maintains
this temperature, so it begins to cool and equilibrate to the ambient
temperature. The rate at which this cooling occurs depends on the
temperature differential between the body and the environment
(elevated body temperatures and cool ambient temperatures will
increase this rate), but as a general rule, the body cools at a rate
of about one degree per hour during the first twelve hours.

Livor mortis (also called hypostasis) is the pooling of the blood in
the body due to gravity and the lack of blood circulation as a result
of the cessation of cardiac activity (Knight, 2002). These factors
cause the blood to pool in the lowest points of the body, giving the
skin a purplish-red discoloration. Livor mortis typically begins
around thirty minutes to four hours after death, and is most
pronounced approximately twelve hours after death. There are two
recognized stages of livor mortis, which are a function of whether the
blood has begun to coagulate. Prior to blood coagulation, livor is
"unfixed"; if the body is moved, the blood will re-pool in whichever
part of the body is closest to the ground in the new position. Livor
becomes "fixed" when the blood coagulates, preventing the blood from
re-pooling if the body is moved into another position.

Rigor mortis is muscle stiffening caused by the binding together of
muscle fibers. Muscles require a molecule called adenosine
triphosphate (ATP) in order to release from a contracted state
(Knight, 2002); after death, the body's ATP reserves are quickly
exhausted and muscles remain contracted until the muscle fibers
themselves start to decompose. Rigor mortis is typically seen first in
the small muscles of the face and jaw. Rigor generally begins to set
in several hours after death, peaks around twelve hours after death,
and then subsides over the next day or so with decomposition of the
muscle fibers (Knight, 2002). The timing of rigor mortis is dependent
on environmental conditions such as temperature, as well as the
physical activity of the decedent around the time of death.

Decomposition is the process by which organic material is broken down
into simpler forms. It occurs systematically in all biological
organisms with the cessation of normal life functions (Gill-King,
1997; Marks et al., 2009), and begins immediately following death.
Decomposition (also sometimes called postmortem decay) results in many
physical and biochemical changes that can be observed macroscopically
and microscopically. Decomposition occurs through two primary chemical
processes: autolysis and putrefaction. They often occur in tandem, but
one may predominate in certain conditions.

Autolysis (or "self-digestion") is the destruction of cells through
the action of their own enzymes. Autolysis typically occurs most
rapidly in the pancreas and stomach, and may be the predominant
decomposition process in more arid environments.

Putrefaction is the microbial deterioration of tissues caused by the
proliferation of bacteria associated with the digestive system.
Putrefaction causes color changes in the body including various shades
of green, purple, and brown due to the release of pigments from the
breakdown of internal structures. In a process called intravascular
hemolysis, bacteria increases throughout the circulatory system,
resulting in a significant darkening of the vessels, a process often
referred to as marbling.

Also associated with putrefaction is the production of gases. These
gases, primarily located in the abdomen, cause the body to bloat. This
bloating can cause the affected areas of the body to expand
dramatically. Over time the affected areas may rupture or the gas will
subside naturally. Skin slippage, or shedding of the epidermis from
the body caused by the deterioration of the junction between the
dermis and epidermis, is also associated with early decomposition
processes. Many local environmental factors affect the decomposition
process, including temperature, moisture, and soil chemistry, but the
processes of autolysis and putrefaction are still responsible for the
chemical breakdown of tissues (Knight, 2002).

In some cases, conditions may prevent or significantly delay the
complete decomposition of remains. Artifactual preservation refers to
the preservation of a body or tissues by natural processes, chemical
substances, or by the destruction of bacteria which may significantly
alter normal decomposition processes. Such preservation may be related
to the environment (such as aridity, moisture, or extremely cold
temperatures), or the depositional substrate (such as being in contact
with preservative compounds in tree bark, pine needles, or decomposing
leaves). Preservation may also be facilitated by body coverings
including clothing (especially leather such as boots and jackets),
plastic, or airtight caskets. The use of chemicals such as embalming
compounds will also significantly delay decomposition.

Mummification is the preservation of remains by desiccation or drying
out (Figure 5.1). The process of mummification requires relatively low
humidity, and is more likely to occur in individuals who have a low
amount of body fat. Although it can occur naturally, some ancient
cultures, such as the societies of ancient Egypt, practiced deliberate
mummification of bodies. In a forensic context, mummification is
likely to occur in arid areas (whether hot or cold). The skin may turn
a dark brown color and become leathery in texture (Galloway, 1997).
Despite the dried nature of the outer tissue layers, there may
continue to be insect activity (e.g., maggots and carrion beetles)
occurring below the skin, especially if the remains contain moisture
from bodily fluids and remaining soft tissues (Galloway, 1997). Tannic
acids such as those found in peat bogs also tend to facilitate natural
mummification (Box 5.3).

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FIGURE 5.1
BOX 5.3

BOG BODIES

Grauballe Man – A well-preserved "bog body" from Denmark
(historypbl.worldpress.com)

Bodies that have become mummified in a peat bog have been called "bog
bodies" or "bog people." Most of these specimens have been discovered
in northwestern Europe, including many that are estimated to be
thousands of years old. It is believed that many of the individuals
were killed and deposited into the peat bogs as part of cultural
practices which may have included human sacrifice (Fischer, 1998). The
conditions in peat bogs that facilitate this degree of preservation
include having low oxygen, low temperature, and high acidity. The soft
tissues such as the skin and organs are often well preserved while the
bones and teeth are often decalcified due to the acidity (Brothwell
and Gill-Robinson, 2002). The most famous bog body is that of
"Grauballe Man," a very well-preserved body discovered in 1952 in
Denmark. It is estimated to date from the 3rd century BC.

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Saponification is the process of the conversion of fatty tissue to
adipocere (Gill-King, 1997; Clark et al., 1997; Ubelaker and Zarenko,
2011). Saponification usually occurs in unoxygenated, alkaline,
semi-moist to wet environments, and is therefore more likely to occur
in remains deposited in water. Saponification can also occur in
remains from moist, airtight crypts or burials, and may be accelerated
by bacteria. Adipocere, sometimes referred to as "grave wax," is
typically white in color and waxy in consistency, but can vary from
white to grey or tan to black, and can be semi-soft to hard in
consistency (Figure 5.2). Once formed, adipocere is relatively
resistant to subsequent change, and can preserve many of the soft
tissues. Saponification can occur in as little as three weeks, but
onset takes place typically at one to two months.

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FIGURE 5.2

Differential decomposition refers to the premature, irregular, or
disproportional decomposition in an area or areas of the body. One of
three causes is usually responsible: an injury that exposes blood and
tissues and provides a portal for scavengers, exposure to physical or
chemical agents such as heat or corrosive acids, or prior local
bacterial infection such as an abscess or cellulitis. In a forensic
context, differential decomposition is important to detect and
document if present, since it may provide information about an
individual's health just prior to death, or it may suggest trauma or
foul play. For example, if a body that is otherwise fairly well
preserved shows significant decomposition in the area of the neck,
that region should be carefully examined for evidence of possible
injury since it is not an area that would normally be expected to
decompose at a faster rate.

The bones and teeth of the skeleton are much more durable and take
longer to decompose than soft tissues. Skeletonization refers to the
completion of soft tissue decomposition, where only the hard tissues
of the skeleton remain. The skeleton also undergoes postmortem
changes, which are discussed in the following section.

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