θυρεοειδής

Thureoeidḗs comes from Greek thureos (a door-shaped shield, from thura, door) and eidos (form, shape). The word meant shield-shaped. Galen applied it to the laryngeal cartilage — what we now call the thyroid cartilage, the structure that forms the 'Adam's apple.' The gland wrapped around this cartilage inherited the name by proximity. The thyroid gland is not shield-shaped. The cartilage is. The gland got the wrong name for the right reason.

The thyroid gland produces hormones (T3 and T4) that regulate metabolism — the rate at which the body converts food to energy. Too much thyroid hormone (hyperthyroidism) causes weight loss, anxiety, and rapid heartbeat. Too little (hypothyroidism) causes weight gain, fatigue, and depression. The gland that was named for a shield controls the body's thermostat.

Goiter — an enlargement of the thyroid — was one of the most visible diseases in history. Iodine deficiency causes the thyroid to swell as it attempts to produce hormones without a key ingredient. Alpine regions of Europe, far from the sea and its iodine-rich food, had endemic goiter for centuries. The Swiss painter Hans Holbein depicted goiters in his portraits. Iodized salt, introduced in the 1920s, eliminated endemic goiter in most developed countries.

The thyroid was one of the first endocrine glands to be understood, partly because its effects are so dramatic and partly because it is accessible to surgery. Thyroidectomy — surgical removal — has been performed since the nineteenth century. Theodor Kocher of Bern won the Nobel Prize in 1909 for his work on thyroid surgery. The Greek shield-shaped cartilage led to the naming of the gland that led to the understanding of hormones that led to endocrinology. The word started the science.