What is the thyroid?
The thyroid gland lies at the base of the neck. It is shaped like a butterfly and wraps around the windpipe (trachea) beneath the voice box (larynx). Its parts include:
wings of the butterfly (left and right lobes)
body of the butterfly (isthmus, joining the left and right lobes)
there is a small part that lies over the voice-box (pyramidal lobe).
When the thyroid is larger than normal it is called a goitre. Lumps in the thyroid are called nodules. Most thyroid nodules are benign but some can be cancerous.
What does the thyroid do?
Glands that release hormones into the blood stream are called endocrine glands, the thyroid is the largest endocrine gland of the body.
The thyroid produces hormones that are released into the blood and carried to every tissue in the body. There are two types of thyroid hormone, tri-iodothyronine (T3) and thyroxine (T4). These hormones control the speed at which the cells work (metabolism), and are important in brain development and growth in children. These hormones also determine how sensitive other organs are to endocrine hormones. Thyroid hormone is made in cells called follicular cells.
The amount of thyroid hormone in the blood stream is controlled by the pituitary gland. The pituitary gland, is a small endocrine gland that sits under the brain. It releases a hormone into the blood called thyroid stimulating hormone (TSH). When doctors order thyroid tests, they will look at all three of these hormones (T3, T4 and TSH) but TSH is the most important.
Too much thyroid hormone is called hyperthyroidism or an overactive thyroid. This can lead to heart palpitations, trouble sleeping, shaky hands, muscle weakness, nervousness or anxiety, feeling hot and problems with your menstrual periods.
Not enough thyroid hormone is called hypothyroidism or an underactive thyroid. This can lead to weight gain, lethargy, intolerance to cold weather, depression, constipation and problems with hair loss and dry skin.