The thyroid is a butterfly-shaped gland at the front of the neck, with two lobes beside the windpipe joined by a narrow isthmus. It makes thyroid hormones that set the body's metabolic rate, and calcitonin, which has a minor role in calcium balance. Because it is enclosed by pretracheal fascia, it moves up when you swallow.
| Location | Anterior neck, lobes on either side of the larynx and trachea from the oblique line of the thyroid cartilage to about the sixth tracheal ring, isthmus over tracheal rings 2-4, deep to the infrahyoid (strap) muscles |
|---|---|
| Secretes |
|
| Nerve Supply | Sympathetic fibres from the cervical ganglia (vasomotor) |
| Blood Supply | Superior thyroid artery; Inferior thyroid artery; Thyroid ima artery (inconstant) |
| Venous drainage |
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| Lymphatic drainage |
Produces T4 and T3, which raise metabolic rate, support growth and brain development, and affect heart rate and body temperature. Parafollicular (C) cells make calcitonin, which lowers blood calcium.
Thyroid swellings move with swallowing, which helps tell them from other neck lumps. Thyroid surgery risks injury to the recurrent laryngeal nerves (hoarse voice) and the external branch of the superior laryngeal nerve (weak high-pitched voice), and accidental removal of the parathyroids (low calcium). Overactivity (Graves disease) and underactivity (Hashimoto thyroiditis) are very common and affect energy, weight, heart rate and temperature tolerance.
Enlargement of the thyroid, diffuse or nodular, from iodine deficiency, autoimmune disease or nodules; may compress the trachea or oesophagus.
Excess thyroid hormone, most often from Graves disease, causing weight loss, tremor, palpitations, heat intolerance and anxiety.
Insufficient thyroid hormone, commonly from Hashimoto thyroiditis, causing tiredness, weight gain, cold intolerance, constipation and dry skin.
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