The Thyroid Gland

Body

Anatomy of the thyroid gland

The thyroid gland is located in the front of the neck (just above the breastbone and below the Adam's apple). The small, two-inch gland consists of two lobes, one on each side of the windpipe, connected by a small bridge of thyroid tissue called the isthmus.

The thyroid tissue is made up of two types of cells: follicular cells and parafollicular cells. Most of the thyroid tissue consists of the follicular cells, which secrete the iodine-containing thyroid hormones. They consist of thyroxine (T4) and triiodothyronine (T3). The parafollicular cells (also called C cells) secrete the hormone calcitonin. Calcitonin is a weak hormone that helps in the regulation of calcium in some animals. In humans, calcitonin has only a  minor role in calcium regulation. When the thyroid is completely removed because of cancer or disease, the removal of these C cells produces no problems with calcium regulation. The follicular cells require an adequate supply of iodine in order to produce the thyroid hormones.

Functions of the thyroid gland

The thyroid plays an important role in regulating the body's metabolism. Virtually every tissue in the body is affected or regulated by thyroid hormone. It regulates our metabolism, brain development and function, skin, hair, eyes, heart, and intestine function. The thyroid hormones enter into tissues and regulate how those tissues produce or do not produce certain proteins. The thyroid function is controlled by the pituitary, which sits at the base of the brain. The pituitary is controlled by a region in the brain called the hypothalamus.

How a thyroid disorder affects a woman's body

The functions of the thyroid gland have much to do with a woman's reproductive system, particularly if the thyroid is overactive or underactive. Effects of this imbalance in hormone levels may have the following effects on a woman's body:

Puberty and menstruation - Thyroid disorders can cause abnormally early or late onset of puberty and menstruation. In addition, abnormally high or low levels of thyroid hormone can cause very light or very heavy menstrual periods, very irregular menstrual periods, or absent menstrual periods (a condition called amenorrhea).

Reproduction - An overactive or underactive thyroid may also affect ovulation (the release of an egg for fertilization). Thyroid disorders may prevent ovulation from occurring at all. In addition, the ovaries are at an increased risk for cyst development if the woman has an underactive thyroid (hypothyroid). Severe hypothyroidism can actually cause milk production in the breast, while preventing ovulation.

Pregnancy and postpartum - Thyroid disorders during pregnancy can harm the fetus and may lead to thyroid problems in the mother after birth, such as postpartum thyroiditis.

Menopause - Thyroid disorders may cause the early onset of menopause (before age 40 or in the early 40s). In addition, some symptoms of hyperthyroidism (overactive thyroid), such as lack of menstruation, hot flashes, insomnia, and mood swings may be mistaken for early menopause. Treating hyperthyroidism sometimes can alleviate symptoms of, or the actual onset of, early menopause.

What are thyroid function tests?

Thyroid function tests are common procedures done to determine how well the thyroid is functioning. Some of the most common thyroid function tests include the following:

Blood tests. This test is done to measure the level of thyroid-stimulating hormone (TSH) in the blood which helps determine thyroid function. High levels of the hormone indicate an underactive thyroid. In addition, a blood test can measure levels of hormones thyroxine (T4) and triiodothyronine (T3), and less often, a protein called thyroglobulin.

Ultrasound exam of the thyroid gland. An ultrasound scan is a diagnostic technique that uses high-frequency sound waves to create an image of the internal organs. It's done to detect signs of abnormal enlargement, or nodules, on the thyroid, and to guide biopsies of concerning nodules.

Thyroid scans using radioactive iodine or technetium (another radioactive element). This test helps determine the cause of abnormal thyroid function. This may be important in deciding whether a person will need a total thyroidectomy or partial thyroidectomy.