The human body consists of approximately 37 trillion cells [1]. That’s a mindblowing number – 37 million million. Your one body contains thousands of times more cells than there are humans on the planet Earth.
If you consider that there are between 100 and 400 billion stars in the Milky Way [2], then you have about 100 times more cells in your body than there are stars in the Milky Way galaxy.
But it does not stop at the galaxy of cells in your body. Every single cell is a city of its own, consisting of a city wall (cell membrane), central management (genes), army of workers (RNA & proteins), soldiers & gatekeepers (proteins and other molecules in the cell membrane that shuttle molecules in and out of the cell) and communication system (such as hormones and other signal exchange with other cells).Every cell also contains hundreds to thousands of its own tiny energy factories, called mitochondria [3]. These are separate living micro-organisms with their own DNA. They live in complete symbiosis with our cells. They have given up their independent living and produce energy for us in exchange for a sheltered environment within our cells with food delivery. (When you lie in bed under a blanket and feel the heat build up, consider that this is due to the dissipation of energy produced by this army of trillions of little energy factories.)
Just like mitochondria, our cells themselves also gave up independent living as individual organisms a long time ago in our evolutionary past. They benefited from collaboration and specialisation just like human societies do. The evolution of multicellular life led to a spectacular creative explosion of body forms and ways of living, just like large-scale collaboration in modern civilisation has yielded tremendous benefits and advances.
Cells in multicellular organisms like humans gave up independence on one key condition: every cell carries the same full genetic code of the organism, so that reproduction of the organism means reproduction of every cell’s DNA and no one cell or cell type is favoured above another. (One can look at cancer as a form of rebellion of cells no longer willing to control or limit their own replication in the interest of the bigger organism, but rather appropriating more resources and replicating to the detriment of the rest of the organism.)
And then there’s even more… Apart from our own cells and mitochondria, each of our bodies houses a myriad other passengers, free-riders, contributors and partners. For example, the human intestinal tract houses about 100 trillion bacteria [4], both ‘good’ and ‘bad’.The good bacteria help us process food, help extract and manufacture nutrients from our food, help keep our intestinal tract healthy and protect us from the bad bacteria. They do all this in exchange for a fraction of the food we eat. (We have many other micro-organisms and organisms living in and on our body, including parasites, but let’s not spoil dinner by looking at them more closely.)
So it is no exaggeration to say that your body is a galaxy, teeming and jostling with life and activity from hairtip to toetip. It is something to stand in awe of. And if you consider that every atom in your body was produced in the stars, then we can say that each of us is a galaxy made of stardust.
References
[1] Website: https://handling-solutions.eppendorf.com/cell-handling/about-cells-and-culture/detailview/news/how-many-cells-are-in-your-body-probably-more-than-you-think/. Last accessed: 2020/11/15.
[2] Website: https://www.universetoday.com/22285/facts-about-the-milky-way/. Last accessed: 2020/11/15.
[3] Website: https://www.britannica.com/science/mitochondrion. Last accessed: 2020/11/15.
[4] Website: https://www.health.harvard.edu/staying-healthy/can-gut-bacteria-improve-your-health. Last accessed: 2020/11/15.
Image credits
Galaxy Photo by Bryan Goff on Unsplash.
Cells Photo by National Cancer Institute on Unsplash