The human body is an incredibly complex system, with different parts and processes that sustain life. Even after the brain and heart stop functioning, some processes and cells in the body continue for hours or even days after death. So what is the very last thing to die in the human body after death? Let’s explore this fascinating question.
Defining Death
To understand what dies last, we first need to define death itself. Legally and medically, a person is declared dead when there is irreversible loss of all brain function and blood circulation. The specific criteria include:
- No response to stimuli
- No reflexes
- No breathing
- No pulse
Once the heart stops beating, blood circulation halts and oxygen is no longer delivered to tissues. The brain will die within 5-7 minutes without oxygen. But death is really a process, and some cells and processes can continue even after the clinical threshold of death.
Post-Mortem Processes
After the heart and brain have stopped, the body goes through various post-mortem changes as cells gradually die off. Here are some key processes that occur:
- Cell death – Cells die at different rates based on their resilience and oxygen needs
- Loss of homeostasis – The body loses its natural balance and ability to self-regulate
- Autolysis – Cells digest themselves by breaking down proteins and membranes
- Putrefaction – Bacteria decompose tissues, releasing gases that bloat the body
- Livor mortis – Blood settles via gravity, creating discolored pools in the body
- Rigor mortis – Muscles stiffen temporarily due to chemical changes
- Decomposition – The body eventually breaks down entirely through bacterial action
These processes don’t necessarily occur in a set sequence, and some take longer than others. Rigor mortis, for example, peaks around 12 hours after death and dissipates around 24 hours. Decomposition can take weeks or months depending on conditions. So what process keeps going after everything else has ended?
The Last Remaining Sign of Life
Hair and Nails Appear to “Grow”
You may have heard that hair and nails continue growing after death. This is just an urban legend – hair and nails don’t have any living processes that allow true growth. However, as the skin around the hair and nails retracts from dehydration, the hair and nails appear longer. This gives the illusion of additional growth.
Lingering Lab Results
Certain lab tests on blood and tissue may still show results up to 48 hours after death. For example, a blood glucose level check may show an artificial spike due to cell breakdown. However, these lab results don’t mean the cells are still alive in a meaningful way.
The Winner: Gene Activity
The very last living process in the body after death is gene activity. Gene expression and transcription of RNA messages continues for up to several days in some cell types after the heart stops, research shows. The cells that remain alive the longest include:
- Skin cells
- Embryonic cells
- Stem cells
- Cells involved in inflammation
- Hair follicles
In a 2019 study, scientists analyzed zebrafish and mice cells after death. They found thousands of genes remained active for up to 4 days, regulating stress response, development, and inflammation. Other cell functions had ceased.
This posthumous gene activity does not indicate life itself or consciousness. However, it shows that the process of death at a cellular level can take time, with a gradual shutdown combined with flurries of genetic activity. Even without blood circulation or oxygen, the most hardy cells put up a fight.
Why Do Some Cells Stay Alive?
Why do certain cells continue gene transcription and activity after we die? Here are a few key reasons:
Different Oxygen Needs
Some cells simply don’t require as much oxygen to function compared to others. They can withstand the oxygen depletion for a time. Cells like skin cells and hair follicle cells are more resilient than cells that need constant high oxygen levels like brain neurons.
Backup Energy Sources
Cells have different ways of producing energy without oxygen, at least for a while. For example, skin cells can get energy from glycogen stores for many hours after death. This allows them to maintain some normal functions.
Programmed Functions
Some of the genes that remain active after death play roles in essential developmental or stress response programs. These genes essentially continue doing their job because that’s what they are programmed to do. Some inflammation genes fall into this category.
Location
Where cells reside in the body impacts their survival time. Those closer to the surface have access to more oxygen from the environment. Cells deep inside organs deteriorate more rapidly after blood circulation stops.
Post-Mortem Gene Expression
While post-mortem gene transcription does not indicate life, it does have some fascinating implications:
- It refines our understanding of the gradual process of death at the cellular level.
- It shows how some cells are programmed to resist stress and hypoxia.
- It highlights the variability between cell types in resilience.
- It may lead to advances in preserving organs for transplant.
- It provides insights into inflammation and healing that could have medical applications.
Research into this phenomenon is ongoing. There are likely many more factors that influence which genes remain active and for how long after clinical death.
Conclusion
While the brain, heart, and lungs shut down rapidly after death, the story doesn’t necessarily end there. Some hardy cells can continue basic gene transcription and expression for hours or days. Skin cells, hair follicle cells, stem cells, and inflammatory cells tend to have the longest post-mortem lifespan. Exactly which genes remain active depends on the cell’s functions and programmed stress response.
This posthumous gene activity doesn’t indicate continued life but rather a gradual unfolding of cell death. In the end, though, the very last bastion of activity in the deceased human body is the expression of a few determined genes. The heart, brain, and organs may die, but some cells put up a final fight before surrendering to death’s silence. Understanding this phenomenon could have significant implications for medicine, organ transplant, and the very meaning of life itself.