So now let's look at another endocrine gland or the thyroid gland. The thyroid gland is a
butterfly shaped gland in the anterior of the neck on the trachea inferior to the larynx and
consists of a structure known as the isthmus, which is a mask that connects 2 lateral lobes.
Within the thyroid gland, we have follicles which are made up of hollow spheres of epithelial
follicular cells that are going to produce the glycoprotein, thyroglobulin. Within the follicle,
we have a fluid known as colloid. This is going to contain thyroglobulin plus iodine and is the
precursor to the thyroid hormone. Located on the outside of the follicle are the parafollicular
cells which are going to produce another thyroid hormone known as calcitonin. Notice in this
histology slide the location of the follicle cells, the colloid within the follicle cells, and the
parafollicular cells that are outside of those follicle cells.