After death, blood undergoes several changes influenced by factors like gravity, chemical processes, and the environment. Here's a breakdown of what happens:
Initial Stasis and Pooling
Immediately after death, the circulatory system ceases functioning, and blood flow stops. Gravity causes the blood to settle in the lowest parts of the body, a process called livor mortis or postmortem lividity. This results in a discoloration of the skin in those dependent areas, often appearing as a purplish-red hue.
Postmortem Lividity (Livor Mortis)
- Appearance: Discoloration of the skin due to blood pooling.
- Location: Occurs in the dependent parts of the body (e.g., back if the body is supine, legs if the body is upright).
- Timing: Starts within 30 minutes to 2 hours after death and becomes fixed within 6-12 hours.
- Shifting: If the body's position is changed within the first 6-8 hours after death, the blood can shift and pool in the new dependent areas. This is called "shifting of postmortem lividity."
- Fixation: After approximately 6-8 hours, the blood begins to coagulate within the vessels in the dependent areas, making the lividity "fixed." This means changing the body's position will no longer alter the pattern of lividity.
Coagulation
The blood begins to coagulate (clot) due to the absence of natural anticoagulants that are present in a living body. This coagulation process can contribute to the fixation of livor mortis.
Hemolysis
Hemolysis, the breakdown of red blood cells, begins postmortem. This process releases hemoglobin into the surrounding tissues, which can further contribute to the discoloration associated with livor mortis. The released hemoglobin can also seep into tissues, causing staining.
Putrefaction and Color Changes
As decomposition (putrefaction) progresses, bacteria break down tissues, including blood. This process releases gases and other byproducts, leading to further color changes. The blood may darken or even turn greenish-black.
Factors Influencing Postmortem Blood Changes
Several factors can affect the rate and extent of these changes:
- Temperature: Higher temperatures accelerate decomposition and blood changes.
- Cause of Death: Certain causes of death (e.g., carbon monoxide poisoning) can affect the color of the blood postmortem.
- Body Position: Determines where blood pools and the pattern of livor mortis.
- Age and Health: Can influence the rate of decomposition and blood coagulation.
In summary, postmortem blood undergoes pooling, coagulation, hemolysis, and decomposition, all of which contribute to the visible changes observed in a deceased body. These changes are valuable in estimating the time of death and understanding the circumstances surrounding death.
