Thyroid Gland

About the Thyroid Gland

The thyroid gland is a butterfly shaped organ in the anterior neck at the level of C5 to T1, wrapping around the trachea. It has two lateral lobes connected by an isthmus, weighing approximately 20 to 30 grams. It produces T3 triiodothyronine 10 percent, active and T4 thyroxine 90 percent, prohormone from tyrosine and iodine. TSH from the pituitary stimulates production. T3 and T4 increase basal metabolic rate, heart rate, body temperature, and are essential for brain development. Thyroid follicles contain colloid with thyroglobulin. The parafollicular C cells produce calcitonin, lowering blood calcium, though its physiological role is minor compared to PTH. Hyperthyroidism Graves disease autoimmune TSH receptor antibody causes tachycardia, weight loss, heat intolerance, tremor, exophthalmos. Hypothyroidism Hashimoto thyroiditis causes fatigue, cold intolerance, weight gain, bradycardia, depression. Thyroid nodules are common and mostly benign; fine needle aspiration cytology, reported using the Bethesda system, helps identify the minority that are malignant. Papillary carcinoma, the most common type of thyroid cancer, generally has an excellent prognosis. Goiter is thyroid enlargement from iodine deficiency or autoimmune disease.