Abstract When life ceases, a sequence of physiological and physical changes begins. The most important include loss of thermoregulation, cessation of blood circulation, gravitational settling of blood in the dependent parts of the body, and depletion of cellular energy in the muscles. These phenomena have traditionally formed the basis for estimating the postmortem interval; however, their value increases when they are interpreted together with environmental conditions and the circumstances of the death scene. Figure (1): An educational diagram illustrating the three traditional early postmortem changes: algor mortis, livor mortis, and rigor mortis. Physiological Basis During life, the nervous system, circulation, and metabolism maintain homeostasis. After death, effective energy production, blood circulation, and thermoregulation cease. Body temperature gradually approaches the ambient temperature, while blood moves under the influence of gravity toward the dependent parts of the body. The muscles later become stiff because of chemical changes and depletion of ATP. As time progresses, autolysis and putrefaction develop, making the early postmortem signs less useful. Connection to Forensic Evidence At the death scene, the specialist examines body temperature, the distribution of livor mortis, the degree of rigor mortis, environmental conditions, clothing, body position, and the time the person was last seen alive. These findings are not used to determine an exact time of death; rather, they help construct an approximate time range. Recent reviews emphasize that algor mortis, livor mortis, and rigor mortis are mainly useful during the early postmortem period, and that their accuracy is influenced by multiple internal and external factors. Educational Applied Example Educational example: A body is found inside a cold room. If the investigator relies on body cooling alone, the postmortem interval may be overestimated. Therefore, room temperature, clothing, body mass, rigor mortis, and livor mortis should all be incorporated into the interpretation. This example demonstrates that physiology provides useful indicators, but the forensic context gives those indicators their practical meaning. Key Learning Points • Understanding homeostasis explains why the body changes after vital functions cease. • The three traditional postmortem signs complement one another and should not be treated as independent substitutes. • Estimation of the postmortem interval provides a probable time range rather than an exact time of death. Article Conclusion This topic shows that physiological knowledge is not merely theoretical; it contributes to the interpretation of biological evidence in a forensic context. Nevertheless, professional conclusions should be based on the integration of clinical or postmortem examination, death-scene findings, and laboratory tests rather than on any single sign.