Your thyroid gland is in the front of your neck, below the larynx (voice box). The small, 2-inch gland has 2 lobes, one on each side of the windpipe. The lobes are connected by tissue called the isthmus.
The thyroid tissue is made up of 2 types of cells: follicular cells and parafollicular cells. Most of the thyroid tissue is made of the follicular cells. These cells secrete hormones that contain iodine. The hormones are called thyroxine (T4) and triiodothyronine (T3). The parafollicular cells secrete the hormone calcitonin. The thyroid needs iodine to make the hormones.
The thyroid plays an important role in regulating your body's metabolism and calcium balance. It also plays a role in fertility, growth, and skin health. The T4 and T3 hormones tell every tissue in your body to make proteins. T4 and T3 also increase the amount of oxygen used by cells. The harder the cells work, the harder the organs work. The calcitonin hormone works together with the parathyroid hormone to regulate calcium levels in your body.
Levels of hormones secreted by the thyroid are controlled by a hormone made by the pituitary gland. This hormone is in turn is controlled by the hypothalamus.