Library · Physiology
Calcium balance
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Almost all of the body's calcium is stored in the skeleton: about 99 percent. What is left lives in the soft tissues and in the extracellular fluid, the fluid that bathes the cells. Think of a huge warehouse and a tiny amount circulating outside it.
Of the calcium that does circulate, about half travels free, as an ion, and only that free fraction is biologically active.
Keeping it where it belongs is the job of three hormones: parathyroid hormone, calcitonin and calcitriol, which is active vitamin D. When it needs to go up, parathyroid hormone works on three fronts at once: the kidney, bone and intestine.
If free calcium falls, nerves and muscles become more excitable, and that can go as far as tetany: contractions the muscle cannot release.
In brief
The skeleton holds about 99 percent of the body's calcium; the rest sits in soft tissue and extracellular fluid.
A huge warehouse, bone, and a tiny amount circulating outside it.
About half of what circulates is free, in ionized form, and that fraction is the biologically active one.
Three hormones regulate it: parathyroid hormone, calcitonin and calcitriol; the first acts on the kidney, bone and intestine to raise it.
If free calcium falls, neuromuscular excitability rises and tetany can follow.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingCalcium Homeostasis and Disorders: An Integrated Clinical and Laboratory Approach, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated