It would be interesting what this functional reserve is, right? The microbiome perhaps, or intracellular minerals? Some other thing we haven’t even identified?
> It would be interesting what this functional reserve is, right?
It is most likely not a single thing.
Looking for "the functional reserve" is like looking for which part of an airplane is the "multiple redundancy". Or which line of code is the "fault tolerance" in google's code base. It is not a single part, it is all the parts working together.
Just looking at the kidney example (which is not the only kind of function we can describe having functional reserve.) functional reserve is that there are two kidneys, and each kidney have multiple renal pyramids, and if this or that part of the kidney functions worse other parts compensate and will work overtime.
Depletion of functional reserve is not something literally running out (like a fuel tank running empty), it is more like a marauding gang shooting computers in a cloud data center. Sure initially all works as it used to, because the system identifies the damaged components and routes the processing to other ones. But if they keep it up they will damage enough that the data center will keel over and can't do what it could do before.
(No, I'm not saying that a human body is literally a data center, or literally an airplane. What I'm saying is that all three shares the common theme that some process is maintained in the presence of faults.)
In case of kidneys, my understanding is that only a certain subset of glomerular cells are actively filtrating blood at any given point. The other cells form the functional reserve, and start to become active once the other cells age out, or are disrupted due to an event (like poisoning, such as mycotoxin damage from eating moldy food). Once the functional reserve is exhausted however, no new cells can become active and you are left with whatever dwindling GFR you have, until you get a transplant.
With the vascular system you have example arterial elasticity which is an important measure of vascular health. When your blood vessels become less elastic it does not immediately cause symptoms, but it increases the risk of heart disease and stroke. This is also why periodontitis and gum disease is a predictor for vascular diseases: Bacteria enter the bloodstream through inflamed oral mucosa and form plaques along the blood vessels.
>"This is also why periodontitis and gum disease is a predictor for vascular diseases: Bacteria enter the bloodstream through inflamed oral mucosa and form plaques along the blood vessels."
And yet in the year 2025 dental care is globally treated as seperate from other healthcare, a strange historical artifact that clings on.
Story from the US: had an awful tooth infection (from a known dead tooth) that I tried to ride out, half my face was swollen up, even my eye looked half shut. Well after a day of this I couldn't take the pain. Called my doctor "we don't pull teeth, you have to call a dentist." So I called a dozen dentist and was told either "we aren't taking new patients" or "we can't get you in for 6 months".
I ended up just driving to a dentist and saying "look at my fucking face! Pull this fucking tooth out!" Finally a dentist was able to spare 30 seconds to yank it. Bill was something like $750.
I got a doctor to pull an internal tooth that had formed a cyst around it, a maxillofacial surgeon.
The dentist quoted $1300 but said insurance wouldn’t cover it, it’d be out of pocket. The surgeon did it (I was awake with local anesthesia) for $300 but insurance paid an additional $4000.
Before all this, A PE owned dentist office (the one that didn’t have the six month wait) had told me two years before that the pain I was experiencing was because I had periodontal disease and that I just needed to get a periodontal cleaning (which cost $750 and didn’t help at all, also conveniently not done by a dentist but a dental hygienist). This turned out to be very dangerous because the cyst was pushing and wearing away at my nose bone, and if I’d waited any longer my nose may have sunk into my face.
It’s definitely maddening the hoops one has to go through to get proper dental care in the US.
Regardless of the financial and administrative issues, dentistry is still far more an art than a science. Go to 10 different dentists for any serious condition and you'll likely receive 10 different treatment plans. In most cases they're making good faith recommendations but there's a huge amount of subjectivity and personal bias involved.
Physicians have recently started embracing evidence-based medicine with documented best practice treatment guidelines so hopefully a similar cultural change will come to dentistry in time.
And you couldn’t just board a plane to Mexico or anywhere down south and get the job done for half the price including said flight? People keep complaining but don’t realize that no place is perfect in this world.
Some places are significantly worse than all others in the same wealth class though.
Somebody further up quoted such insane numbers - $750 for a proper periodontal cleaning? That's usually ~50 to 80€ in Germany. For a _full_ self payer.
Those prices and the health system creating them are utter insanity.
Why though? You demand a service that you can get cheaper abroad. You can’t change the health system but you can travel to a socially developed country that hasn’t yet fallen victim of corruption
