The thyroid is a butterfly-shaped gland in the front of the neck, just below the larynx. Its hormones set the pace of metabolism in almost every cell.
Location
Two lobes lie on either side of the trachea, joined by a thin isthmus below the cricoid cartilage. The gland moves up when the patient swallows because it is attached to the larynx.
Making hormone
Thyroid cells take up iodine from the blood and attach it to a protein stored in small sacs called follicles. They release mostly T4, which the tissues convert to the more active T3.
What it does
Thyroid hormone raises oxygen use, heat production and heart rate. It is also needed for normal brain growth in infants, which is why newborns are screened.
Control
TSH from the pituitary drives the thyroid. High TSH with low T4 points to an underactive thyroid; low TSH with high T4 points to an overactive one.
| Feature | Too much (hyperthyroid) | Too little (hypothyroid) |
|---|---|---|
| Heart | Fast rate, palpitations | Slow rate |
| Temperature | Heat intolerance, sweating | Cold intolerance |
| Weight | Loss despite good appetite | Gain |
| Bowels | Frequent stools | Constipation |
| Reflexes | Brisk | Slow relaxation |
At the bedside
Feel the thyroid while the patient sips water, checking for enlargement or nodules as the gland rises. Pair the neck exam with TSH and free T4.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).