This is an interesting question that many people are eager to talk about. In this blog post, I will go through what happens to the human body after death in a scientific manner.
NOTE: This is still a work in progress. This requires a lot of reading and I hope to complete this within the next two weeks.
rrefer to this as well: https://www.slideserve.com/azize/post-mortem-changes-powerpoint-ppt-presentation
Classifying Death
TODO: Update everything here. make stuff sound more professional and fix grammar
Most people think that death is a single moment. One second you are alive, the next you are not! Scientifically, death is NOT a single event – It’s a chain of phsyiological events where each event leads to the next like dominoes.
It usually begins with cardiac death, which occurs when the myocardium fails to contract effectively (also called cardiac arrest). When the heart stops, the cariac output will be zero, resulting the cardiac perfusion to fall to zero. Without the systemic circulation, the delivery of oxygen to cells and tissues stop while carbon dioxide accumulates. This will lead to global hypoxemia and tissue hypoxia.
The failed systemic circulation will also result in hypoperfusion of the brain stem. This prolonged ischemia of the brain will result in cerebral hypoxia (potentially even complete cerebral anoxia), neuroglycopenia and many other complications.
This results in (anoxic) ischemic depolarization.
- The Na+/K+-ATPase pump is what maintains the transmembrane gradients of K+ and Na+ ions.
- During ischemia, this pump fails and will result in the loss of the ion gradients.
- This will cause the extracellular K+ cocentrations to increase along with an influx of Na+ and Ca2+ ions into the cell.
- This results in net depolarization of the nueronal membrane.
- This will trigger the release of certain neurotransmitters such as glutamate which can bind to and activate various receptors like the NMDA receptor – which will lead to further Ca2+ influx.
- This will lead to excitotoxic injury of the brain stem.
This will result in the permanent loss of brain functions. This is called “brain death”.
Cardiac arrest might be reversible if intervened quickly with cardiopulmonary resuscitation and/or other advanced cardiac life support techniques. However, it depends on a lot of other factors as well. If the patient is not recuscitated within 2 to 5 (or 3 to 10???) minutes, it would cause irreversible ischemic injury to the brain. After that, even if circulation is restored or maintained artifically, the patient will considered to be “dead”. This is because the medicolegal definition states brain death to be the formal definition of death.
Brain death will result in autonomic functions to stop from working immediately.
The medulla oblongata is what detects too low carbon dioxide levels and signals the diaphragm and intercoastal muscles to contract. Upon brain death, it will no longer send any impulses to the phrenic and intercoastal nerves. Therefore, apnoea occurs.
Without respiration, oxygen levels in the blood will fall while the carbox dioxide level increases, resulting in hypercapnia. This will lead to systemtic hypoxia and a severe acid-base imbalance.
If brain death occurs first (before cardiac arrest), as cardiac myocytes are now oxygen deprived, they will switch to performing anerobic metabolism, resulting in the formation and accumulation of lactic acid, which will weaken the heart’s contractility. Therefore, it will result in bradychardia and will soon progress in to complete asystole.
The loss of hypothalamic function will stop the body’s ability to perform thermoregulation. Under normal circumstances, the hypothalamus maintains homeostasis based on the input from peripheral thermoreceptors and will initiate to perform a response such as vasodilation, vasoconstriction, shivering, or sweating to stabilize the bodys’ temperature. Once the hypothalamic neurons undergo ischemic necrosis, this autonomic function will fail completely, resulting in the body to become poikilothermic. This means the body will passively reach equilibrium to the ambient temperature using basic heat exchange mechanisms like conduction, convection and radiation.
As the mid brain does not function, pupillary reflexes are also lost. As the vasomotor tone is lost, the blood pressure will collapse. Along with these, all other brainstem reflexes such as the gag reflex and the corneal relfex will disappear.
it will also fail the respiratory centers of the brain simeltanously.
If circulation and oxygen delivery are not restored, the body goes to biological death. This is when the cellular changes become ivveversible. With neurons now suffering from anoxia and neuroglycopenia, they would undergo ischemic depolarization and excitotoxic injury resulting in the permanent loss of the brains’ functionality.
Eventually, cellular necrosis begins throughout the body. In the mean time, lysosomal enzymes leak out, resulting in autolysis. Once it reaches this stage, there is no going back. Upon cardiac arrest,
This is what to refer to as brain death. The patient will have fixed and dilated pupils, no gag relfex nor corneal reflex and might not breathe on their own even when the carbon dioxide level rises. In most countries, including the UK and Sri Lanka, brain death is considered as “legal death” even if circulation is being maintained artificially.
On the broader level, there’s “somatic death”. This is the death of the whole body, including cellular death. This happens unvenvly across different tissues. The brain cells will die within minutes after loss of blood circulation but muscle cells, skin cells, and more popularly, corneal cells might remain viable for hours (depending on environmental factors). This is why corneal transplants and skin grafts can still be harvested from recent dead bodies.
After legal death – determined by cardiac criteria (irrversible asystole resulting in no systemic circulation) and neurological criteria (brain death caused by whatever the reason), the body will be issued the death certificate.
Death
The myocardium fails to contract, resulting in cardiac arrest. Systemtic circulation stops and the perfusion pressure falls all the way down to zero. This results in oxygen delivery to stop which will make carbon dioxide to accumulate resulting in global hypoxemia and tissue hypoxia. The brain that also suffers cerebral hypoxia/anoxia along with neorglycopenia with will cause irreversible ischemic injury within 2-5 minutes (or 3-10???). This will result in breain death and none of your brainstem reflex will function, even if circulation is artificially maintained. This is considered to be the medicolegal definition of of “death”.
Upom the irreversiblee cease of neuronal activity, the body won’t have the capacity for thought, awareness, or sensation. Your body becomes unconsicous, will loose it’s reflexes and the ability to react to stimuli. Right after death happens, the body encounters it’s first sign of insensibility, the loss of sensation followed by the loss of voluntary power. I personally believe that the concept of “soul” dies along with brain death as everything we associate with being a “person” disappears completely. YOLO!
Within a few minutes, the retinal blood vessels appear segmented or fragmented. It can be seen with an opthalmoscope. It is called the “Kevorkian Sign”. This will appear very quickly after death and will last for approximately an hour.
The pupils will also be dilated mildly.
As blood circulation stops after cadiac arrest, oxygenated blood does not reach the skin anymore. Without capillary perfusion, the pink tone from oxyheamoglobin disappears. This will make the skin turn pale. Since the blood pressure is gone, capillaries won’t refill and the heamoglobin trapped in them will dexoygenate quickly, making it even more pale. This process is called “algor mortis” and usually starts 15-30 minutes after death.
After an hour, the cornea turns hazy.
In the mean time, “algor mortis” also takes place. As no metabolic activity takes place, the body will have no way to regulate the temperature. Therefore, the heat dissipates into the environment at about 0.4C to 2C per hour until it reaches equilibreium with the sorrounding environment (0.4C in the winter and 0.7C in the summer). This will of course vary depending on the clothing around the body and the fat content along with a lot of other factors, like wind (which results in heat loss via convection). Some regions of the body will lose heat faster than the others. For example, parts like the face, hands and feet tend to cool more quickly because they have a larger surface area with little fat and musle sorrounding them. Note that fat is insulative. Therefore, the more fat you have, the longer it takes your body to reach equilibrium. Compared to these, the core of the body cools down much slower, specially the thoracic cavity and the abdominal cavity. Algor mortis is an important concept as one of the main time of death estimation in forensic medical studies is based on this. In this case, the rectal temperature is used as it is considered to be the closest to the body core temperature (BCT).
The BCT drop can be graphed and divided into three stages. This graph takes a sigmoid shape.
Stage 1 is called the Isothermic phase, stage 2 is called the steep decline phase and stage 3 is called the gradual decrease phase.
Ensure you have a complete understanding of the newton’s laws of cooling before using the Glaister equation to substitute the rectal temperature to calculate the “PMI” (Post Moterm Interval) to adjust the values and/or offsets accordingly.
Below is the glaister equation:
- PMI = (98.7 °F − rectal temperature of the decedent (°F)) / (T)
- Here, T = 1.5 if ambient temperature < 32 °F.
- And, T = 0.75 if ambient temperature ≥32 °F.
This formula is appropriate mostly for environments with typical cooling environments.
Additionally, the Henssge Nomogram is also used to estimate the PMI. Click here to read more about using this accurately.
After two hours, the intraocular pressure will drop from the normal 20 mmHg to zero, increasing the flaccidity of the eye.
After 20 to 30 minutes, the
After 3 to 6 hours, if the eyelids are open, all of the dust present in the atmosphere will get deposited into the sclera, resulting in two brownish triangular shaped opacities to the left and the right of the cornea. This is known as “Tâche Noire Sclérotique”.
Along with that, after approximately 5 hours, the corneal opacity will start increasing.
When I come to putrefication, talk about it here, talk about the eye and how it is resistant to it: https://www.prepladder.com/neet-pg-study-material/forensic-medicine/thanatology-types-of-death-post-mortem-changes
notes
right after death
- unconsciousness
- lose reflexes
- no reaction to stimuli
- muscular flaccidity
- mild dilated pupils
- eyelids usually closed incompletly, resuling in tache noire
hypostatis vs livor mortis vs post moterm lividity seperate out the rectal temperature part and the equations talk only about death talk about other crap later
blanching
livor mortis of internal organs + find images for everything mentioned above livor mortis color (toxicology) tardieu spots
rigor mortis cadaveric spasm their difference
algor
decomposition marbling putrefaction active decay skeletanization mummification
maggot and fly eggs and stuff, durations, images, when
Shortly after death, due to relaxation of muscles, including the iris, the eyes will dilate (pupils grow larger). However, with the onset of rigor mortis, the pupils constrict. They may be unevenly dilated or constricted, and may even appear oval.
autolysis
cover time estimations forensic side of things look at a case study
refer to MI myocardial necrosis from simpsons textbook also about other organs