Bone as the calcium reservoir, and osteoporosis

Bone is the calcium-phosphate reservoir of the mineral loop. Simulation shows serum calcium held at setpoint while a sustained demand depletes the bone reserve monotonically: osteoporosis is reservoir depletion (post-menopausal/age), not a local lesion. Bone identity is cited from the musculoskeletal volume.

Bone is the calcium-phosphate reservoir. Under chronic calcium demand the loop holds serum calcium at setpoint by withdrawing from the bone reserve, which depletes monotonically — the reservoir/setpoint trade-off and the substrate of osteoporosis.

The reservoir/setpoint trade-off

Under a sustained calcium demand, serum calcium stays at setpoint (maximum deviation 0.0316) while the bone reserve declines monotonically from 1.00 to 0.43 (normalized). The value defended is purchased from the reservoir; sustained demand empties it.

This is osteoporosis as a reservoir failure rather than a local lesion: post-menopausal and age-related loss raise net withdrawal (estrogen loss) and lower loop gain. Bone identity is owned by the musculoskeletal volume (DNA SSOT); here bone appears in the mineral-reservoir role, not as a fork.