For any X with turnover much faster than aging (i.e. decades), if we see the level of X increase/decrease on the timescale of a human lifetime, then that is not due to permanent “accumulation of X” or “depletion of X”; it is due to increase/decrease in the rate of creation/removal of X.
Is it not just how accumulation and depletion exactly occur in biological systems? Not even specifically at the cellular level?
A (likely) counterexample is elastin: it seems to not be broken down at all in humans. So if new elastin is produced (e.g. as part of a wound-healing response), it just sticks around indefinitely.
This is in contrast to homeostatic equilibrium, which describes most things in biological systems, but not elastin.
Writers do sometimes use “accumulation”/”depletion” to refer to things in homeostatic equilibrium, but I find this terminology misleading at best, and in most cases I think the writer theirself is confused about the distinction and why it matters.
Must be a local thing, then. (Or it’s opposite is a local thing, and I’m just used to systems crawling leisurely to some equilibrium, like seed banks, and to systems where the equilibrium is hard to define for a given moment, like internal parasite loads.)
I don’t understand this:
For any X with turnover much faster than aging (i.e. decades), if we see the level of X increase/decrease on the timescale of a human lifetime, then that is not due to permanent “accumulation of X” or “depletion of X”; it is due to increase/decrease in the rate of creation/removal of X.
Is it not just how accumulation and depletion exactly occur in biological systems? Not even specifically at the cellular level?
A (likely) counterexample is elastin: it seems to not be broken down at all in humans. So if new elastin is produced (e.g. as part of a wound-healing response), it just sticks around indefinitely.
This is in contrast to homeostatic equilibrium, which describes most things in biological systems, but not elastin.
Writers do sometimes use “accumulation”/”depletion” to refer to things in homeostatic equilibrium, but I find this terminology misleading at best, and in most cases I think the writer theirself is confused about the distinction and why it matters.
Must be a local thing, then. (Or it’s opposite is a local thing, and I’m just used to systems crawling leisurely to some equilibrium, like seed banks, and to systems where the equilibrium is hard to define for a given moment, like internal parasite loads.)