Nutrition Science and Everyday Application - beta v 0.1

Calcium: Critical for Bones and Throughout
the Body
As discussed on the previous page, bones are made up of two components: inorganic
minerals and a protein matrix. Minerals, which make up 65% of bone tissue, are what gives
bones their hardness. Calcium and phosphorus together form hydroxyapatite crystals, the
main mineral component of bone. Other minerals, including magnesium, fluoride, sodium,
and potassium, play supporting roles. This page focuses on calcium, and we’ll cover
potassium, magnesium, and fluoride on the following page. (Sodium and potassium are
covered in the electrolyte section of this text.)
CALCIUM FUNCTIONS AND REGULATION
Calcium is the most abundant mineral in the body. Most of the body’s calcium—more than
99% of it—is stored in bone, where it’s important for bone strength and structure. The
remaining 1% of the body’s calcium is found in the blood and soft tissues, but it is here
that calcium performs its most critical functions. For example, calcium is required for the
transmission of every nerve impulse, electrical signals sent from one nerve cell to another.
It’s also required for every cycle of muscle contraction and relaxation. With inadequate
calcium, muscles can’t relax, and instead become stiff and contract involuntarily, a condition
known astetany. Calcium also plays vital roles in blood pressure regulation, blood clotting,
enzyme activation, hormone secretion, and signaling between cells. 1
The many roles of calcium around the body are critical to daily survival, so maintaining
homeostasis, or a steady state, of blood calcium levels is a high priority. The body rigorously
controls blood calcium levels in a very tight range. If blood calcium drops, your body initiates
several mechanisms to restore homeostasis, including drawing calcium from the bone. While
the calcium stored in bone is important for long-term strength and structure of bone, it also
serves as a calcium reserve that can be drawn upon to support the vital functions of calcium
in the body, should blood calcium drop too low.
Two endocrine glands are key players in the regulation of blood calcium concentrations:
the thyroid gland and parathyroid glands. The thyroid gland is a small, butterfly-shaped gland
located at the base of the neck. It secretes a hormone called calcitonin. There are four
parathyroid glands, each about the size of a pea and located at the back of the thyroid gland.
They secrete a hormone called parathyroid hormone (PTH).
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