Endocrine Embryology

The branchial arches, also known as pharyngeal or visceral arches, are embryonic structures seen in the development of vertebrates that serve as precursors for many structures of the face, neck, and head. These arches are composed of a central core of mesoderm, which is covered externally by ectoderm and internally by endoderm. Indentations between arches are known as the pharyngeal clefts, or grooves, externally and the pharyngeal pouches internally. Each pharyngeal arch contains cartilage and muscular components, which are supplied by a cranial nerve (derived from neural crest cells), and an artery, known as a pharyngeal aortic arch. Some of these aortic arches go on to form the great vessels near the heart.

The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck, spanning the regions between the C5 and T1 vertebrae and encircling the anterolateral trachea. The left and right lobes of the thyroid gland are connected by a central isthmus. Important processes in metabolism, growth, cardiac function, and calcium homeostasis are regulated by the thyroid hormones (thyroxine and triiodothyronine) and calcitonin.