Animation 39.3: Hormonal Regulation of Calcium

INTRODUCTION

Calcium ions play an essential role in many cellular processes, and the body must closely regulate calcium levels within a narrow physiological range. Even relatively small changes in blood calcium levels can have dramatic effects, including muscle and brain dysfunction, heart failure, and even death. Despite its essential role, 99 percent of calcium is found in the bones. Bones therefore act as an important reservoir of calcium for use throughout the body.

Calcium homeostasis is controlled by three hormones: calcitonin, parathyroid hormone, and vitamin D. Note that while vitamin D is considered a vitamin because it is required in the diet, it is also considered a hormone because it is synthesized in certain locations in the body and distributed in the blood to other tissues where it exerts its action. Each of these hormones acts on bone cells and other tissues to raise or lower the concentration of calcium in the blood.

CONCLUSION

While calcitonin plays a significant role in calcium regulation in many animals, its importance in humans is not as clear. Even when the thyroid gland is removed, the human body is still able to regulate calcium levels in the blood. Parathyroid hormone (PTH) and vitamin D appear to be far more important in calcium regulation. These two hormones act on bone cells to regulate calcium resorption and deposition, and also act on the kidney and digestive system to promote calcium uptake and retention. While the action of vitamin D in the short term is to increase blood calcium levels, it also acts to promote bone deposition when the levels of calcium in the blood become elevated.

Textbook Reference: Key Concept 39.4 Hormones Regulate Metabolism and the Internal Environment

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