The major function of the thyroid gland is to produce thyroid hormones, according to HowStuffWorks. One hormone is called thyroxine and the other triiodothyronine, or T4 and T3. Together, they regulate the growth and development of nearly every system in the body.
The thyroid takes up iodine from the blood to make these hormones, claims HowStuffWorks, and they are stored in the thyroid until they are needed. When the body does need thyroid hormone, the gland releases them into the blood stream. Once in the cells, the hormones are converted into other hormones that help regulate the rate at which the cells take up oxygen and use it as fuel.
In some people, the thyroid gland is either underactive or overactive, explains HowStuffWorks. The first condition is known as hypothyroidism, while the second is called hyperthyroidism. If the thyroid is underactive, the processes of the body generally slow down. The person may be tired all the time, or may become depressed or confused. People who have hyperthyroidism may be nervous, suffer heart palpitations, sweating, trembling and weight loss. Fortunately, thyroid diseases are treatable.
The thyroid gland is found in the neck, says WebMD. It's made up of two lobes on each side of the trachea, or windpipe. It is well supplied with blood vessels.