Have you ever heard of the Ship of Theseus? A famous paradox born from Greek mythology, it follows a ship whose parts were entirely replaced over time as Theseus traveled. The tale raises a fascinating question: once every single wooden plank has been swapped for a new one, is it still the same ship, or is it a completely new object? In many ways, this exact concept can be applied directly to your own body. Are you the same if your cells constantly replenish?
Much like how you have an end date, so do your cells. They also die and get renewed in a continuous cycle known as cell turnover1. A process that is defined as producing new cells to replace lost and injured cells. While certain parts of your body, like the neurons in your brain, are exempt from this cycle and stay with you for life, most of your body is constantly refreshing its cells. In fact, your body replaces about 80 grams of cells every single day, mostly within your blood and skin2.
However, as you get older the cell turnover rate starts to slow down, meaning, damaged cells stay in your body for longer3. While this decline affects all organs, it is extremely important for body parts that are required for your survival, such as your lungs, kidneys, liver etc.. Just think to yourself, how much plain water did you drink today?
Truth of the matter is, the organs you started out with when you were younger are not the same organs you have today. You can even see this with your own eyes. A knee that was scraped during your childhood might have only taken a week to heal, and now the same injury takes a month4. Like it or not, your organs slow down and become more vulnerable to damage as cell turnover drops. It is imperative to get frequent check-ups to ensure everything is in working order, be it by blood tests or imaging.
References:
1O'Brien LE. Tissue Homeostasis and Non-Homeostasis: From Cell Life Cycles to Organ States. Annu Rev Cell Dev Biol. 2022 Oct 6;38:395-418. doi: 10.1146/annurev-cellbio-120420-114855. Epub 2022 Jul 18. PMID: 35850152; PMCID: PMC10182861.
2Sender, R., Milo, R. The distribution of cellular turnover in the human body. Nat Med 27, 45–48 (2021). https://doi.org/10.1038/s41591-020-01182-9
3Wagner W, Bork S, Horn P, Krunic D, Walenda T, Diehlmann A, Benes V, Blake J, Huber FX, Eckstein V, Boukamp P, Ho AD. Aging and replicative senescence have related effects on human stem and progenitor cells. PLoS One. 2009 Jun 9;4(6):e5846. doi: 10.1371/journal.pone.0005846. PMID: 19513108; PMCID: PMC2688074.
4Blair MJ, Jones JD, Woessner AE, Quinn KP. Skin Structure-Function Relationships and the Wound Healing Response to Intrinsic Aging. Adv Wound Care (New Rochelle). 2020 Mar 1;9(3):127-143. doi: 10.1089/wound.2019.1021. Epub 2020 Jan 24. PMID: 31993254; PMCID: PMC6985772.
