This lecture examines the thyroid gland and the parathyroid glands. For each, we briefly review the gross and microscopic anatomy, its physiology, and the consequences of dysfunction. Thyroid dysfunction can lead to cretinism, myxedema, Graves' disease, and other pathologies. Parathyroid dysfunction can lead to disorders including bony demineralization, high calcium levels, duodenal ulcers, kidney stones, and behavioral disorders.