Post mortem secundary changes
These are changes that occur in the cadaver from the moment the first signs of cadaveric putrefaction appear until the complete destruction or disappearance of the cadaver.
Therefore, putrefaction is the first change that occurs within this group, all others are secondary and are closely related to the process of putrefaction.
Imbibition is defined as the displacement of a viscous fluid by another immiscible fluid. Regarding postmortem alterations, two types of imbibition exist: hemolytic and icteric.
- Hemolytic imbibition: is the result of intravascular hemolysis suffered by erythrocytes, whereby hemoglobin is released into the environment to later solubilize with tissue fluids and thus diffuse throughout the tissues of the carcass. The coloration acquired is a reddish color that spreads throughout the animal as the necropsy is performed and tends to darken more as it oxidizes over time.
- Icteric imbibition: consists of the diffusion of bile and its pigments through the walls of the gallbladder, changing the color of the organs that contact the wall or are close to it, such as, for example, the liver tissue, which acquires a well-defined green-yellow-green color.
The tissues acquire a gray, green or black coloration depending on the state of putrefaction. The responsible for this coloration are the bacteria that produce hydrogen sulfide that when combined with the iron of the hemoglobin produce iron sulfide, a black pigment that together with others gives the different tonalities.
It is produced by the accumulation of gases in the cavities, tissues and solid organs of the body produced by bacterial fermentation.
Some of the gases that originate are: methane, carbon dioxide, ammonia, hydrogen sulfide gas, etc. Therefore, the odor from putrefaction originates from the combination of these gases with small amounts of mercaptan.
The gases can give rise to various postmortem alterations such as:
- Distension of cavities, as well as emphysematous appearance of parenchymal organs (spleen, liver, etc.).
- Rupture of the cavitary organs due to the high pressure exerted inside them together with the already existing weakening of the walls due to the putrefaction process.
- Displacement of the organs, especially at intestinal level. It is important to differentiate this alteration from the displacement of the organs antemortem. If the alteration is postmortem, they will not have an intense red color due to the collapse of the hilum and the development of a passive hyperemia (hemorrhagic infarction).
It is a biological process characterized by the postmortem decomposition or degradation of tissues and all organic matter contained in the cadaver. This decomposition is carried out by the enzymatic action of bacteria, fungi, arthropods and vertebrates on the tissues and body fluids until the complete degradation of the body.
Of vital importance in this process are the aerobic commensal bacteria of the respiratory and digestive tract, as well as external bacteria that invade dead tissues of the organism. This results in a rapid drop in pH which, together with the lack of oxygen, favors the rapid growth of anaerobic microorganisms with high fermentation capacity located mainly in the gastrointestinal tract.
The putrefaction periods are
- Chromatic: It begins 24-36 hours postmortem. In small or medium-sized animals a greenish coloration is established in the abdomen, starting in the inguinal area and extending towards the thorax and extremities. This coloration is due to the degradative action of the bacteria on the hemoglobin that is embedded in this area. It is frequent that all these findings are masked by the normal coloration of the skin and by the hair, wool or feathers. As this process progresses, the skin adnexa begin to separate easily.
- Emphysematous: it is established from 60-72 hours postmortem and lasts approximately one week depending on climatic conditions. It derives from gas production (see above) which results in postmortem emphysema, displacement and rupture. The amount of gas produced depends on the type of diet consumed by the animal, as well as the amount of food ingested.
- Reductive:it is due to the exit of the gas produced in the previous phase as a consequence of the rupture of the tissues that contained such gas, beginning to collapse the carcass and decompress the cavities. Finally, the gas contained in the parenchymal tissues and muscles disappears.
- Coliquative: at this stage there is maceration and softening of the parenchymatous organs and viscous liquefaction of the soft tissues (except for the bones, which will be the last remnant of the cadaver).
- Gross studyIt is necessary to consider that the description of gross lesions is performed according to the necropsy technique, which has to be orderly, complete and systematic. The first thing to do is to indicate the organ, and then look at a series of gross characteristics such as: