Post Mortem Changes
A)Death
is usually a process rather than an event; Clinical and Molecular Death
B)The peri-mortem and immediate post-mortem changes
C)The early changes; the ‘algor-livor-rigor’ triplets and their role in helping to estimate time since death.
D)The late changes and the ultimate disintegration of the organic body into its inorganic components.
A)Death is usually a process rather than an event; Clinical and Molecular Death
Death is declared with cessation of all vital functions such as nervous, circulatory and respiratory systems. But we need to know that death is a process not an event and, while the cells of some tissues are still alive and even capable of movement (such as fibroblasts, leucocytes and muscle fibres, etc) others are dying or dead.
Clinical death: Clinical death is defined as the irreversible cessation of functioning of the brain, heart and lungs resulting in complete loss of sensibility and ability to move the body. However, certain parts of the body such as the muscles can be still made to respond to an electrical, thermal or chemical stimulus, suggesting the reality that death has not resulted completely. Thus death is a process rather than an event. Clinical death is declared clinically when the three vital organs, namely the heart, lungs and brain fail to function and is confirmed by a flat ECG, absence of breath sounds and a flat EEG. Often these criteria are known as the Harvard’s criteria of assessing death.
Molecular death: Molecular death is defined as ultimate death of all cellular elements. After clinical death, various tissues survive till the oxygen supply to them is adequate. When the oxygen reserve in the cells gets depleted, cellular death or molecular death sets in. Generally molecular death is not complete before 2 to 4 hours of somatic death. Molecular death can be confirmed by absence of any response to an electrical, thermal or chemical stimulus in the tissues. The nervous tissue dies rapidly in about 5 minutes while the muscle tissue lives up to 3 to 4 hours, after the cessation of the circulation.
B) The peri-mortem and immediate post-mortem changes
The early postmortem changes are those that occur immediately at or around the time of death. These changes include cessation of respiration, cessation of circulation, ocular changes (absent reflexes, vacant stare), pallor of skin, and primary flaccidity (loss of muscle tone).
Eye changes: At death eyes look staring and vacant, pupils assuming nearly mid-position. Corneal reflex is lost. Cornea looses its glistening appearance, becomes dull and opaque and looks like dimmed glass. Eyeball sinks into orbit. Pupils are dilated at death but may constrict due to rigor mortis. Rise in potassium in vitreous humor is seen. Retinal vessels changes can be seen too ( trucking of blood vessels in retinal vessels)
Skin changes: Skin looses elasticity. Skin becomes pale white and pallor. Lips turn brownish, and hard due to drying. Skin may have yellowish/reddish discolouration due to jaundice or poisoning due to carbon monoxide and hydrogen cyanide. If death is associated with agonal spasm, the face remains congested, bluish black for sometime after death. Postmortem lividity - change in the skin is of great medicolegal importance.
C)The early changes; the ‘algor-livor-rigor’ triplets and their role in helping to estimate time since death
Algor mortis (Postmortem cooling): Algor mortis is defined as the cooling of the dead body. After death, the dead body behaves like an inert object and looses heat by the conduction, convection and radiation, till it reaches equilibrium with the temperature of its surroundings. However, during the first 2 to 3 hours after somatic death, ‘living tissues’ and ‘bacterial action’ continues to produce heat. It is not uniform. In temperate climate, the cooling rate is:
• In first 2 to 3 hours there is no cooling
• In the next 6 hours it is about 1.5°C/hour
• In later 6 to 12 hours it is about 0.9°C to 1.2°C/hour.
Thus, the whole body surface gets cooled by 10 to 12 hours of death. But the internal organs cool slowly (cools by 18-24 hours of death).Thus time since death can be calculated as postmortem interval (PMI).
PMI = ( Normal body temperature – Rectal temperature of the cadaver)/Rate of temperature fall per hour
Postmortem lividity (Livor mortis)
Postmortem lividity is the purplish or reddish purple areas of discoloration of skin and organs after death due to accumulation of blood in dependent parts of the body and seen through the skin. After death, blood in its fluid state gravitates into the toneless capillaries and venules in the dependent parts of body and causes capillovenous distension, which through the skin imparts a discoloration to the area involved. It can involve skin, all tissues and viscera. In body which was supine at death, it is seen on the back, ears and posterior aspect of the body except the contact areas like bony prominences, buttocks, the neck area with a tight collar, neck tie, etc. Time since death can be estimated from lividity as well. It is said that if pressure applied by a thumb blanches the area, the time since death is less than 8 hours. If the area does not blanch, lividity is fixed and the time since death is more than 8 hours.
Rigor mortis
Rigor mortis is the postmortem stiffening/rigidity of the muscles in a dead body. The changes occurring under these phenomena are mainly due to the irreversible fusion of two contractile elements namely actin and myosin filament of muscle fibres into a dehydrated stiff gel, making them remain in a rigid state. This will persist till the actin and myosin filaments undergo autolysis. Rigor mortis is basically due to the depletion of adenosine triphosphate (ATP) reserve from the muscle. It is reported that when the ATP level falls to 85 per cent of normal level, rigor mortis is initiated. After death, generation of ATP stops, though consumption continues. With fall of ATP levels, actin and myosin filaments become permanently complexed (fused) into a dehydrated gel and with this rigor mortis sets in.
Time since death the rigor mortis: Rigor mortis sets on within 1 to 2 hours after death, and is well developed from head to toes in about 12 hours. It is then maintained for about 12 hours and in about another 12 hours will go off with onset of putrefaction. This is also known as ‘March of rigor’ or ‘Rule of 12’. But when rigor mortis sets in early, it will tend to pass off quickly and vice versa.
D)The late changes and the ultimate disintegration of the organic body into its inorganic components
Late changes are seen in the dead body after 24 hours of death and include a chain of events known as postmortem decomposition (putrefaction). Eventually the body will be reduced to skeleton and the change constitutes ‘skeletonisation’. Process of decomposition begins in some cells while the others are still alive, and this overlap continues for several days in temperate climate. Decomposition involves two processes; autolysis and putrefaction. Each cell release certain enzymes, which are responsible for lysis of the tissues. Organs rich in enzymes undergo autolysis earlier than organs with less amounts of the enzymes. Pancreas autolyses much earlier than the heart.
Putrefaction is the final process observed in the cadaver, leading to the gradual dissolution and liquefaction of the tissues. Putrefaction is due to bacterial fermentation. Certain bacteria can produce proteolytic and other enzymes, mainly lecithinase which are capable of bringing lysis of tissues, e.g. Staphylococcus, Streptococcus, B. proteus, etc. These organisms, which are responsible for putrefaction, are both anaerobic and aerobic. These bacteria originate from the large intestine, from respiratory tract , open skin wounds . After death the protective mechanisms being absent, within a short time they enter the blood vessels and spread rapidly throughout the body. Thus highly vascular organs, situated more proximally to the source of bacteria, are likely to putrefy.
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