The thyroid gland is composed of numerous epithelial thyroid follicles each composed of a central colloid-filled lumen (containing large gelatinous proteins known as thyroglobulin, which are precursors to thyroid hormones) surrounded by follicular cells. Parafollicular (C) cells are located within and between follicles and secrete calcitonin in response to high blood calcium levels.

Follicular cells are what specific type of epithelium?