Calcium and phosphorus metabolism and the Parathyroid Gland

The parathyroid glands comprise a group of endocrine structures (usually 4 in number) that either hug the posterior surface of the thyroid gland or are in close proximity to it. Although exceedingly small in size, they play crucial roles in the maintenance of calcium and phosphorus balance. Their function spans a range of activities, including blood coagulation, modulation of membrane permeability, muscle contraction, neuromuscular excitability, and the regulation of various signal transduction processes within cells. Their importance to the surgeon is usually related to states of overactivity in which hypercalcemia may ensue. Occasionally, these glands also become important in surgical practices when a state of hypocalcemia results, as may occur after total thyroidectomy for goiter or neoplasia. The intricate control systems regulated by the parathyroid glands to maintain calcium and phosphorus balance are the subject of this chapter.