Calcium Regulation
The control of the level of calcium in the blood — kept within a narrow range because calcium is essential for nerve signaling, muscle contraction (including the heartbeat), and blood clotting.
The main controllers
Section titled “The main controllers”- Parathyroid hormone (PTH) — released when blood calcium is low; it raises calcium by drawing it from bone, conserving it in the kidneys, and (via vitamin D) increasing its absorption from food.
- Calcitonin — released when calcium is high; it lowers calcium, though its role in humans is minor.
- Vitamin D (calcitriol) — required for absorbing calcium from the diet.
The calcium reservoir
Section titled “The calcium reservoir”Bone holds the body’s vast calcium store and is constantly drawn on and replenished — so calcium regulation and skeletal health are directly linked.
Key idea
Section titled “Key idea”Blood calcium is held steady mainly by PTH, using bone as a reservoir. See the calcium–phosphate axis.