If all human cells replace themselves every 7 years, why can scars remain on you body your entire life?
In: Biology
1. Not all cells replace themselves every 7 years–some do it much more frequently (e.g. skin cells can last for a week or two, and the lining of your intestines may last a week or less), others are essentially the same cells your entire lifetime (e.g. neurons and parts of your eye). The 7 years thing is a myth.
2. Scar tissue is the result of your body not having true regenerative ability. In a lot of cases, what you have at the end of development is the “best” most complete x you will ever have, and healing is as much about *quickly* patching over wounds to keep you healthy and alive as it is about the much slower, more expensive, and difficult process or replacing what was lost properly. Often, how cells get in that location and know what to do *comes* from developmental processes and related signaling pathways–wound recovery is a different situation, and your cells don’t always intuitively know exactly what was lost. They lack that bigger picture and complete awareness. So, wound recovery via patching is a necessary step, hence, scar tissue and incomplete healing, which can disrupt delicate parts of the body or result in accumulating (permanent) loss of function in time.
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