The Balance of Life and Death in the Human Body
As humans, so many parts of our body are dying and are being replaces, some died before you were even born, some are dead and would not be replaced till you die completely so we humans are made up of both dead, dying, and living parts and these are what keeps us alive. As humans, a big part of our body is dead, is dying and will never be alive again meaning it looks like we are more dead than alive to be living.
As humans, about 330 billion cells of the body's total 30 to 40 trillion cells are being replaced every day and while all the cells are not replaced in one day, within the space of 100 days, about the total amount of cells in the body has been replaced. It isn't like new cells just emerge without the death of a previously existing one, there need to be a previously existing cell death for a new cell to exist and when new cells exist without the death of a previous cell, it can lead to tumors.
Talking about cell death, different cells in the body die at different rate as some cells die faster while some die slower than others, and some do not die at all until you breath your last but there are some that were long dead before you took your first breath. For instance, the cells that help to grow the ossicles in the middle ear were active when you were in the womb and ended their journey there before you were born, and so are many cells that die including the ones responsible for making different organs.
These cells can die in a way known as Apoptosis where the cells are programmed to die by the body. This type of death affects DNA, and cellular machinery which are then recycled but cells can die via another way and this time it is not programmed, it is known as necrosis caused by infection, toxins or extreme environmental condition. When cells die and are replaced in a programmed manner, we can see it like the body performing maintenance routine.
In the body, while there are trillions of cells, we have about 200 different types of cells. These cells are the building block of our entirety including our organs, tissues, and even our neurons which are responsible for our thoughts, actions, memories and consciousness. With Neurons, they make new connections and cut out others are we learn and unlearn while the brain is growing but when the brain is grown, the neurons remain and this is why brain injuries are often almost permanent in adult. I said almost because scientists have seen that in the hippocampus, neurons can regrow with 1/3 of the neurons being trimmed and new connections made through a person's lifetime.
The body is majorly made up of fat and muscle cells and these cells are the one that live the longest as they can stay for decades with the muscle cells in the heart staying the longest. Cells that build the bones stay for about 10 years, while about 80% of the cells that are often replaced are blood cells especially the red blood cells that last about 120 days but these cells still live longer compared to white blood cells that lasts only hours. colon cells are replaced in less than 1 week while skin cells are replaced on a daily basis. About 500 million skin cells are being replaced daily.
About 2/3 of the human body mass is made up of cells that will die and regenerate over a lifetime. But then, majority of what makes up our body isn't alive, like a lot of our body mass is made by cells and not made of cells like mucus, lymph, spinal fluid, vitreous humor, blood, and tears. Other non living things include calcium in our bones and minerals in our teeth, other non-living things things that make up humans include keratin that makes up our nails and hair, and even the red blood cells are not living as they have no nucleus, no mitochondria, no gene and they can't replicate. Connective tissues are also made by cells and not made of cells, so a large size of things that make up our body are not alive. They are made by cells and not made of cells.
The human body is a remarkable blend of living and non-living components, with a dynamic balance of cell death and renewal that sustains life. Understanding the complexity of our existence and the continuous interplay between life and death within us help us understand that the ongoing cycle is essential for maintaining health and vitality.
Read More
https://www.sciencemag.org/news/2013/06/atomic-bombs-help-solve-brain-mystery
https://doi.org/10.1016/j.cell.2013.05.002
https://www.nationalgeographic.com/science/article/how-many-cells-are-in-your-body
https://pubmed.ncbi.nlm.nih.gov/23829164
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002533
https://www.scientificamerican.com/article/our-bodies-replace-billions-of-cells-every-day/
https://www.ncbi.nlm.nih.gov/books/NBK557588/
https://www.nature.com/articles/s41591-020-01182-9?proof=t
http://jdsjournal.com/retrieve/pii/S0923181104000982
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3678251/
https://www.mskcc.org/cancer-care/patient-education/facts-about-blood-and-blood-cells
http://scienceline.ucsb.edu/getkey.php?key=7116
https://www.acs.org/content/acs/en/pressroom/newsreleases/2011/may/the-skinny-on-how-shed-skin-reduces-indoor-air-pollution.html
To think that all these replacement and emergence happens without us having to literally fall sick and get back up again is amazing, nature indeed has everything perfectly planned out.
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When we think about life and death of a whole organism is easy! But that is happening all the time and it is a very important cycle where the imbalance can be associated to diseases like cancer!