Section One: the Role of Calcium and Calcium Regulating Hormones

CALCIUM Calcium ion plays a key role in many fundamental biologic processes including muscle contraction, blood coagulation, enzyme activity, neural excitability, hormone release, and membrane permeability, in addition to being an essential structural component of the skeleton. Therefore, the precise control of calcium ion in extracellular fluids is vital to the health of humans and animals. To maintain a constant concentration of blood calcium, despite marked variations in intake and excretion, endocrine control mechanisms have evolved that consist primarily of the interactions of three major hormones. Although the direct roles of parathyroid hormone (PTH), calcitonin (CT), and vitamin D frequently are emphasized in the control of blood calcium, other hormones such as adrenal corticosteroids, estrogens, thyroxine, somatotropin, and glucagon may contribute to the maintenance of calcium homeostasis under certain conditions.