Thyroid Gland Location, Anatomy, Parts and Pictures

The thyroid gland is the one of the largest endocrine gland in the body lying  in the front part of the neck. It plays a central role in the body’s metabolism by secreting the thyroid hormones, thyroxine (T4) and triiodothyronine (T3), which increases the basal metabolic rate of cells. It also secretes the hormone calcitonin which is important for regulating calcium deposition.

Anatomy of the Thyroid Gland

The thyroid gland weights about 15 to 20 grams in adults and lies immediately below the larynx, anterior to the trachea and extends to either side of these structures. It is studded by four parathyroid glands that secrete parathyroid hormone (PTH) which regulate calcium levels in the blood. The thyroid gland is made up of many  follicles that are lined with cuboidal epithelium cells. The follicles are filled with colloid that contains thyroglobulin to which the thyroid hormones are attached. These follicles have the capacity to store thyroid hormones for 2 to 3 months.

Picture from Wikimedia Commons

Parts of the Thyroid Gland

The thyroid is a bilobular gland surrounded by a fibrous capsule and can be divided into the following parts :

  • Right lobe that lies to the right side (lateral) of the larynx and trachea
  • Left lobe that lies to the left side (lateral) of the larynx and trachea
  • Isthmus which is the central part of the gland that connects the two lobes

Connective tissue attached to the fibrous capsule of the thyroid gland secures it to the tracheal rings and cricoid cartilage.

Picture from Wikimedia Commons

Blood Vessels of the Thyroid Gland

Arteries of the Thyroid Gland
The thyroid gland is one of the most highly vascularized glands in the body. The thyroid arteries can be divided into superior and inferior thyroid arteries on each side (left and right). The superior thyroid arteries arise from the external carotid arteries. The inferior thyroid arteries arise from the thyrocervical trunk of the subclavian arteries.

Both the superior and inferior thyroid arteries divide into several branches within the thyroid gland. Sometimes an accessory artery known as the thyroid ima artery may arise from the brachiocephalic trunk, arch of the aorta, right common carotid artery or subclavian arteries. This artery primarily supplies the isthmus of the thyroid gland when present.

Veins of Thyroid Gland.
Venous blood is drained from the thyroid gland by the thyroid plexus of veins which empty into three pairs of thyroid veins – superior thyroid, middle thyroid and inferior thyroid veins. The superior thyroid and middle thyroid veins then drain into the internal jugular veins, while the inferior thyroid veins empty into the brachiocephalic vein.

Lymphatic Drainage of Thyroid Gland
The lymphatic vessels from the thyroid gland drain into the prelaryngeal, pretracheal and paratracheal lymph nodes. This in turn drains into the superior cervical and inferior deep cervical lymph nodes, brachiocephalic lymph nodes or directly into the thoracic duct.

Nerves of Thyroid Gland
The nerves to the thyroid gland originate from the cervical sympathetic ganglia – superior, middle and inferior.These nerves control blood flow to the thyroid gland (vasomotor) while hormone secretion is regulated by the thyroid-stimulating hormone (TSH) from the pituitary gland.

Location of the Thyroid Gland

The thyroid gland is located at the levels of C5 to T1 vertebrae lying immediately below the larynx, with the two lobes on each side of and anterior to the trachea. It starts just below the Adam’s apple (thyroid cartilage), about the same level as the cricoid cartilage. The isthmus of the thyroid gland lies in front of the second and third tracheal rings. The gland runs deep to the sternohyoid and sternothyroid muscles and may extend into the superior mediastinum (behind the sternum). It is important to note that the position of the thyroid gland changes during swallowing.

Picture from Wikimedia Commons

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