The thyroid is located in the mid-line of the neck, anterior to the trachea and inferior to the larynx.
The thyroid gland comprises of two lateral lobes and a central isthmus. It is surrounded by a fibrous capsule and located at the level of vertebrae C5-T1.
The pyramidal lobe, an embryological remnant from the descent of the thyroid, typically project upwards from the isthmus, however, there is a wide degree of variation between individuals.
Its primary function is to produce thyroid hormones T3 and T4 following stimulation by TSH.
The thyroid gland is surrounded by a number of important structures.
Its superior border is at the level of vertebrae C4. It forms a median projection, termed the adams apple. Superior to this projection is the superior thyroid notch. The cartilage has both superior and inferior horns.
The cricoid cartilage sits at the level of vertebrae C6. It is the only complete ring of cartilage in the trachea.
It is composed of a posterior component termed the lamina and an anterior component termed the arch. It attaches to first tracheal ring by the cricotracheal ligament.
This ligament connects the inferior border of the thyroid cartilage with the superior border of the cricoid cartilage.
An incision is made through the medium cricothyroid ligament to establish an emergency airway - a cricothyroidotomy.
The parathyroid glands (typically four) are located posterior to the thyroid gland. It is important to note there is a great deal of variety in both the location and number of glands.
They are responsible for the release of parathyroid hormone, a key part of the calcium homeostasis pathways. Due to their location they are frequently removed during thyroidectomy, typically resulting in a transient hypocalcaemia.
A rich blood supply is received from the external carotid artery and the thyrocervical trunk.
The thyroid gland is drained by three pairs of veins.
The recurrent laryngeal nerve is a branch of the vagus nerve (CN X).
The right and left recurrent laryngeal nerves branch off at different levels on the right and left sides. The right side branches of at the level of the subclavian artery whilst the left side branches from at arch of the aorta.
They follow a ‘recurrent’ path upwards through a groove between the trachea and oesophagus. This brings them close to the thyroid gland. The nerve may be damaged during thyroid surgery, typically resulting in a hoarse voice.
The recurrent laryngeal nerve has a number of functions:
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