Aspects of Decomposition

Aspects of Decomposition: A Brief Overview

Kyle Jackman

Animals are complex creatures. The animal can perform such tasks as reproduction, digestion, and simply movement. This is leaving out the more basic functions of respiration, circulation, and various maintenance functions. All of these processes are very complex, from the superficial all the way to the chemical level. Decomposition is one of these processes. It is common belief in our society to believe that death is an event, but that is underestimating its complexity. Death itself is also a process, that is to say, not all cells die at once (Gill-King 1997). Initial inspection after death reveals little change, however the chemical reactions that drive decomposition have already begun, and the results will soon lead to a state of highly efficient chemical cleanup, which is offensive to the senses. Ultimately the lack of oxygen drives these changes (Gill-King 1997), resulting in a state of cellular anarchy, beautiful in its rampant destruction. Like all chemical reactions, decomposition is highly influenced by the ecology of the body, via temperature, humidity, and other such conditions.

In this paper I will address decomposition, and the factors that are involved in its progression. I will begin by describing the chemical and ultrastructural aspects, namely, the physical and chemical constraints to the decompositional process, cell death, and putrefaction. Then I will go on to note the changes in soft tissue, being visible with the naked eye. The aspects of soft tissue change that I will discuss include early and late postmortem changes and modifications to tissue. Lastly I will describe the science of entomology and its importance to the decompositional process. I will provide a background to the science, a discussion of environmental constraints to entomological activity, and end with a discussion of flies and their life cycle.

The chemistry of living cells are maintained at about 37oC, are aqueous, highly catalyzed, and highly segregated (Gill-King 1997). In humans, the repair of cells is carried out by central metabolism, those chemical reactions involved in producing ATP, which are oxygen requiring reactions (Campbell 2001). The lack of circulation following the beginning of death results in a highly anoxic environment. This lack of oxygen sets in motion the decompositional process, which is in a basic sense the bodies self digestion that will eventually lead to a loss of all tissue but skeleton. Many aspects of the environment will influence the longevity of decomposition. Some of these factors are temperature, water, acidity, and partial pressure of oxygen. Temperature is the single most important factor regarding the amount of time spent decomposing (Gill-King 1997). The ambient temperature, while not only being variable according to latitude and altitude, etc., is also affected by various human factors, such as being left in a building (Gill-King 1997). Decomposition is at heart a chemical process, therefore the temperature's effect on decomposition can be understood by Van't Hoff's rule, stating that chemical reactions increase two or more times for every 10oC increase in temperature (Gill-King 1997). The coefficient in most living enzymes is from 1.1-3.0, meaning a 1 to 3 increase in reactions for every 10 degree rise (Gill-King 1997). Also, most enzymes completely denature at about 60 degrees Celsius). Therefore, temperature can greatly increase or greatly retard the process of decomposition with a simple 10oC shift in internal temperature. Mammalian cells are composed of about 77.4% water (Aturaliya et al. 1999). Water has several effects on the decompositus. Water stabilizes temperature, acts as a pH buffer, and provides hydrogen for chemical reactions (Campbell 2001). Various factors such as salinity, movement, and pH of the water can result in an acceleration or retardation of the decompositional process (Gill-King 1997). For example, saline water has high preservative effects (Micozzi 1991). Various hydrolase enzymes use water to break down large organic polymers such as lipids and proteins (Campbell 2001). Also, water promotes salt bonding to the skin, resulting in adipocere formation (Mant et al. 1957). Two other constraints are acidity and oxygen pressure. Changes in cellular pH result in the slowing down of enzyme activity. As the pH lowers, both bacterial and plant activity increases. The amount of oxygen present will affect oxidative processes and bacterial activity in the decompositus. That is to say, bodies that are buried or situated at high altitudes decompose slower than those in a more oxygen rich environment.

As stated previously, the ultimate cause of death is the result of a lack of oxygen. When the circulatory system fails to provide oxygen to somatic cells, the mitochondria in those cells lack the necessary oxygen to finish the electron transport chain, a crucial function for life, because that process provides adenosine triphosphate, the major source of energy for the body (Campbell 2001). When a cell no longer can produce ATP through the transport chain, it begins a fermentative process, due to declining pH levels. This process converts pyruvic acid anaerobically to lactic acid, which provides a small amount of ATP, but not enough to support biosynthesis for very long (Gill-King 1997). Once ATP loss manifests, the first effect is a loss of membrane structure. Unsaturated fatty acids are oxidized without being replaced (Gill-King 1997). This is the beginning of self digestion, known as autolysis.

H. Gill-King defines two stages of autolysis, the early reversible and late irreversible stages. Stage 1 has 7 parts: Anoxia or direct damage to cells lead to drastic reductions in ATP levels; ATP driven biosynthesis of important molecules fail; Membrane bound enzyme systems fail; failure of membrane pumps results in an osmotic imbalance, resulting in cytocavitary flooding and swelling of the cell; a shift to anaerobic fermentative processes, resulting in an acidic pH; increasing acidity results in nuclear chromatin clumping, thus suppressing RNA coding and protein synthesis; Chromatin clumping leads to mitochondrial swelling. Stage 2 has 6 parts: Denatured matrix proteins form matrical flocculent densities (fluffy clumps); the protein portion of the cytoplasm is denatured and appears as grainy clumps; Increased permeability of all membrane bound organelles leads to leakage; hydrolytic enzymes are released from the lysosomes and activated at lowered pH levels, which break down cellular structures; the phospholipids released from the damaged membranes form concentric lamellar myelin bodies, a sign of end stage autolysis; Leakage of hydrolytic