The thyroid is a small gland in the neck located just under the Adam's apple. Shaped like a butterfly, the thyroid plays an important role in a person's health. It affects every organ, tissue, and cell in the body. But what happens during thyroid disease?

Thyroid anatomy
The thyroid produces hormones that help to regulate the body's metabolism and organ functions. The main functions thyroid hormones are to regulate the rate of the metabolic processes being carried out by the various cells in the body.

There are three different types of hormones that are produced and secreted by the thyroid gland. They are:

• calcitonin
• thyroxine or T4
• triiodothyronine or T3

What is thyroid disease?
When the thyroid is not working properly it can affect body weight, energy level, muscle strength, skin health, menstrual cycle (periods), memory, heart rate, and cholesterol level. Thyroid disorders occur when the thyroid gland is not as active as it should be (hypoactive) and when the thyroid is more active than it should be (hyperactive). The thyroid is considered dysfunctional when the thyroid is enlarged, called a "goiter" or "nodule". People with thyroid enlargement can have underactive, overactive or normal thyroid function.

Types of thyroid disorders

Goiter - When the size of the thyroid gland increases, it is known as goiter. This is a very key symptom of any kind of thyroid disease, such as thyroiditis. Goiter can also occur due to deficiency of iodine in the diet, but symptoms vary according to exact cause.

Hypothyroidism - This thyroid disorder is characterized by an underactive thyroid and occurs when the thyroid makes too little of the thyroid hormones that the body needs to function properly. Hypothyroidism is often caused by Hashimoto's disease. Hypothyroidism can also occur during disorders of the thalamus and the pituitary gland, as a result of postpartum thyroiditis( in women after giving birth) and is sometimes noted in inheritance diseases.

Hyperthyroidism - Hyperthyroidism is characterized by an overactive thyroid. When the thyroid gland is overactive, too much of the thyroid hormone is produced for the body to be healthy. Statistically, this condition affects women more than men. In young females, hyperthyroidism is often caused by Graves' disease, when the body's immune system produces proteins similar to pituitary thyroid-stimulatory hormones (TSH) that stimulate the thyroid into making too much thyroid hormone. This results in the entire thyroid becoming enlarged and overactive. Older females may experience another form of hyperthyroidism called toxic nodular goiter when overactive thyroid cells group together and form a lump in the neck. This lump is called a thyroid nodule and it makes more thyroid hormone than the body needs. This sudden release of the thyroid hormones can cause dramatic worsening of symptoms and if not treated fast and properly, can be fatal. Some thyroid disorders cause overactive thyroid, This can, at a later point in time, cause underactive thyroid, due to damage done to the thyroid gland.

Thyroid cancer - This type of cancer is most often found as a lump (or nodule) that is located in the thyroid gland but is not a common type of cancer. Cancers be either non-hormone or hormone productive. However, most thyroid nodules are benign (not cancerous).

Other problems with the thyroid involve:

• antigens in the organ
• immune system malfunctions
• tumors

What causes thyroid disease?  And who is at risk of developing it?  We'll answer your questions in the next section on causes of thyroid disease here.