The endocrine system consists of a series of glands that produce regulatory chemicals, which are known as hormones. The term endocrine means that these glands lack ducts, or exit passageways. They secrete their products directly into the cellular environment. The endocrine system includes these glands: pituitary, pineal, thymus, thyroid, parathyroid, adrenal, pancreatic_islets, ovaries, and testes. We will review some, but not all, of these in our lab.
The thyroid gland helps regulate body metabolism. It produces several hormones, collectively termed the thyroid_hormones (T-3 and T-4). The thyroid contains follicular_cells, which create follicles that contain colloidal substance. The colloidal substance contains thyroglobin.
The thyroid also contains parafollicular_cells (C-cells), which produce calcitonin. Calcitonin controls the removal of calcium from blood.
The parathyroid_glands are located on the posterior side of the thyroid gland. The chief_cells produce parathyroid_hormone (PTH), which causes the removal of calcium from bones. Oxyphil_cells are also present in the parathyroids. They are large and have clear cytoplasm after staining. Their function is still uncertain, but they may produce and/or store reserves of PTH.
The thyroid of the cat wraps around the trachea just below the voice box.