Thyroid

The thyroid gland is a double gland because it consists of two populations of cells of different origin, histological arrangement, and function. The follicular cells secrete thyroxine and triiodothyronine; these hormones regulate development in the infant and young as well as the metabolic rate in the adult. The parafollicular cells of the thyroid are of neural crest origin and secrete calcitonin. This hormone is one of the factors regulating calcium and phosphorous balance in the body.

#77 Monkey & #78 Human Thyroid (#77 not scanned)

The thyroid cells are arranged in follicles so that hormone-producing cells surround a cavity, which is filled with a colloid. The follicles are of various sizes. Observe the relationship of blood vessels to the follicles. The height of the lining follicular epithelial cells reflects the functional state of the follicle. Parathyroid glandular tissue and nerves may be found in these sections.

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