⚗️ Endocrine🟢 BasicThyroid Gland

The Thyroid Gland

An endocrine gland in the front of the neck, made of two lobes joined by an isthmus, that wraps around the upper trachea and secretes thyroid hormones.

Key points

Its two lobes are joined across the midline by an isthmus lying over the second to fourth tracheal rings, and it is enclosed by the pretracheal layer of deep cervical fascia so it moves up on swallowing.
Its blood supply is from the superior thyroid artery (a branch of the external carotid) and the inferior thyroid artery (from the thyrocervical trunk), with a variable thyroidea ima artery in some people.
The recurrent laryngeal nerve runs near the inferior thyroid artery in a variable relationship at the lower pole, so it is at risk in thyroid operations; injury causes hoarseness of the voice.
The external laryngeal nerve lies close to the superior thyroid vessels at the upper pole, where it is at risk during ligation of the superior thyroid artery, and injury weakens the high notes of the voice.
It develops from the floor of the pharynx at the foramen caecum of the tongue and descends along the thyroglossal duct, so a persistent duct can leave a midline thyroglossal cyst that moves on tongue protrusion.
Three sets of veins drain it: the superior and middle thyroid veins to the internal jugular vein, and the inferior thyroid veins to the brachiocephalic veins.

Memory trick

Two nerves, two poles: the external laryngeal nerve hides at the upper pole with the superior thyroid artery, and the recurrent laryngeal nerve at the lower pole with the inferior thyroid artery.

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Key points

Its two lobes are joined across the midline by an isthmus lying over the second to fourth tracheal rings, and it is enclosed by the pretracheal layer of deep cervical fascia so it moves up on swallowing.

Its blood supply is from the superior thyroid artery (a branch of the external carotid) and the inferior thyroid artery (from the thyrocervical trunk), with a variable thyroidea ima artery in some people.

The recurrent laryngeal nerve runs near the inferior thyroid artery in a variable relationship at the lower pole, so it is at risk in thyroid operations; injury causes hoarseness of the voice.

The external laryngeal nerve lies close to the superior thyroid vessels at the upper pole, where it is at risk during ligation of the superior thyroid artery, and injury weakens the high notes of the voice.

It develops from the floor of the pharynx at the foramen caecum of the tongue and descends along the thyroglossal duct, so a persistent duct can leave a midline thyroglossal cyst that moves on tongue protrusion.

Three sets of veins drain it: the superior and middle thyroid veins to the internal jugular vein, and the inferior thyroid veins to the brachiocephalic veins.