The thyroid gland is located in the center of the neck, in front of the trachea (windpipe) and just below the Adam’s apple. The thyroid has a left and a right lobe, which give the gland a butterfly-shaped appearance. The two lobes are connected by a thin strip of thyroid tissue called the isthmus.
The thyroid gland is one of the most important glands in the endocrine system. It uses iodine from food intake to make the hormone thyroxine, which helps regulate body metabolism, bone loss, temperature, heart rate and how forcefully the heart contracts. It also affects growth rate, how quickly food moves through the digestive tract, and how quickly sugar is made and used by the body.
Thyroxine is stored in the thyroid gland and released, as needed, into the blood stream. The release of thyroxine is actually controlled by the pituitary gland, which is located in the brain. The pituitary gland makes the hormone called thyroid stimulating hormone (TSH), which is responsible for stimulating the thyroid to make and release thyroxine. When there is enough or too much thyroxine in the body, the pituitary gland stops releasing TSH. When a patient has a hyperactive thyroid, the effects of the thyroid function are increased.
When a patient has an underactive thyroid, the effects of thyroid function are slowed down. For example, a person with a hyperactive thyroid may experience an increased heart rate or an increased body metabolism, leading to unexplained weight loss. A person with an underactive thyroid may feel extra tired and experience unexplained weight gain.
If a thyroid becomes cancerous, it may affect the lymph nodes located near the trachea and esophagus, as these lymph nodes are responsible for lymphatic drainage of the thyroid gland. If a thyroid becomes enlarged it may affect speech or the ability to talk or swallow. Two nerves that are involved in speech, called the recurrent laryngeal nerves, run right behind each thyroid lobe. These nerves enter the voice box near where the thyroid is closest to the trachea. These nerves help move the vocal chords and control the voice. Injury to or pressure on these nerves can cause hoarseness in the voice, and it can also cause the airway to close down, making breathing difficult. Also, external branches of the superior laryngeal nerve, which play a role in the pitch or volume of the voice, cross just above the thyroid. Injury to these branches could cause a person’s voice to lower and make it difficult to raise his or her voice.