Thyroid gland

Thyroid gland wraps around the trachea just below the larynx, with two lobes connected by a thin isthmus. Follicular cells inside the gland absorb iodine from the bloodstream and build the hormones thyroxine (T4) and triiodothyronine (T3), which influence how quickly cells burn fuel, produce proteins, and generate heat.

The pituitary gland releases thyroid-stimulating hormone (TSH) to regulate production. When circulating T3 and T4 levels drop, TSH rises, prompting the thyroid to work harder; when levels rise, TSH falls, creating a feedback loop that maintains stability. Iodine from seafood, dairy, and iodized salt is essential for this process.

Thyroid hormones shape growth and brain development in infancy, support heart rate, digestion, and muscle function in adulthood, and help the body adapt to cold by boosting metabolism. Thyroid cells also make calcitonin, a hormone that helps regulate calcium levels by signaling bones to store more mineral when blood calcium rises.

Disorders occur when the gland produces too little or too much hormone. Hypothyroidism can cause fatigue, weight gain, and cold intolerance, often due to autoimmune Hashimoto's disease or iodine deficiency. Hyperthyroidism, frequently caused by Graves' disease, speeds metabolism, leading to weight loss, nervousness, and rapid heart rate. Goiters, nodules, or cancer may also develop within the thyroid tissue.

Doctors evaluate thyroid health with blood tests for TSH and hormone levels, ultrasound imaging, and sometimes radioactive iodine uptake scans. Treatments include medication to replace hormones, antithyroid drugs, radioactive iodine to shrink overactive tissue, or surgery. Maintaining adequate iodine intake and monitoring for family history of thyroid disorders help keep this metabolic conductor in tune.