Once a person dies, their body begins a process of decay. This process can be seen through certain external changes which are called post mortem signs of death. There are 4 postmortem signs of death - pallor mortis, algor mortis, rigor mortis, and livor mortis in this order respectively. All these changes occur in the first 24-48 hours after death. Pallor mortis is the first sign. It is when the skin becomes pale because of lack of blood flow to the skin.
Algor mortis is the second sign. It is the change in body temperature post mortem to reach external temperatures.
Rigor mortis is the 3rd stage. In this stage all the muscles stiffen because of cellular degradation called autolysis. It is preceded by primary flaccidity where all the muscles relax because the brain does not send the muscles signals to contract. As cellular degradation continues, it sets the onset of a second phase of relaxation called secondary flaccidity. This whole cycle can take for 24 hours.
Lastly, livor mortis is the pooling of blood due to gravity that appears as a purple colouration.
All these signs are used by forensic experts to determine time of death.
References:
Hall, J. E. (2016). Guyton and Hall textbook of medical physiology. Elsevier. (
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