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Overview of the Endocrine System

Author(s): Center for Educational Outreach, Baylor College of Medicine.

Thyroid Glands

The thyroid gland, consisting of two lobes, is located on the ventral surface of the trachea. It produces two very similar hormones—derived from the amino acid tyrosine—that control metabolism: triiodothyronine (T3) and thyroxine (T4). The thyroid gland plays a crucial role in vertebrate development and maturation, and in homeostasis. It also contains endocrine cells, which secrete calcitonin, a hormone that lowers calcium levels in the blood as part of calcium homeostasis.