enlarged parathyroid gland parathyroid gland hyperplasia overdevelopment or increased size, usually due an increased number of cells of one of the two small, paired endocrine glands, usually found embedded in the connective tissue capsule on the posterior surface of the thyroid gland; they secrete parathyroid hormone (PTH) that regulates calcium and phosphorous metabolism MP:0003493 MPheno.ontology parathyroid hyperplasia