Thyroid gland

Function

The thyroid is a metabolic throttle: a butterfly of follicles over the trachea that concentrates iodide from the blood far more than any other tissue and weaves it into thyroxine (T4) and triiodothyronine (T3). These hormones set the basal metabolic rate of virtually every cell: heart rate, gut motility, bone turnover, temperature and even the speed of thought.

TSH from the pituitary tunes it; the follicles store hormone bound to thyroglobulin in colloid — weeks of reserve, unique among endocrine glands. Parafollicular C-cells add calcitonin, a minor brake on blood calcium.

Blood supply

Superior thyroid (external carotid) and inferior thyroid (subclavian) arteries — one of the body's richest flows per gram.

Nerve supply

Sympathetic from the cervical chain; recurrent laryngeal nerves run in the tracheo-oesophageal groove — the surgeon's paramount respect.

Clinical relevance

Hypothyroidism

Autoimmune (Hashimoto's) or iodine-deficient failure slows everything — fatigue, cold intolerance, weight gain, bradycardia.

Hyperthyroidism

Graves' stimulating antibodies run the engine hot — tremor, heat intolerance, weight loss, and the staring eyes of orbitopathy.

Thyroid nodule/cancer

Most nodules are benign; papillary carcinoma, the commonest malignancy, carries an excellent prognosis.

Related conditions

• Hypothyroidism (underactive thyroid)
• Hyperthyroidism (overactive thyroid)
• Thyroid cancer