What is the Thyroid?

The thyroid is a gland that is found in the front of the neck, under layers of skin and muscle. It is a small gland, but plays a huge role in our overall health. Like other glands in the body, the thyroid is vulnerable to conditions and diseases, such as thyroid cancer. Benign conditions that fall under the umbrella of "thyroid disease" include hypothroidism, hyperthyroidism, Graves' disease, and several others.

Anatomy of the Thyroid

The thyroid is a butterfly-shaped gland located in the neck. It is about 2-3 inches in size and weighs about one ounce. It is composed of two lobes, which are located on either side of the trachea, and connected by tissue called the isthmus. Each lobe contains an upper pole and lower pole. These poles are the highest and lowest points of thyroid tissue. The carotid artery can be found on either side of each lobe. On the right side, the jugular vein is present.

Behind the thyroid rest four parathyroid glands, which regulate calcium levels and are essential for our bodies to function. They are not dependent on the thyroid or affect thyroid function, but do work together to regulate calcium levels. If you are having thyroid surgery, you may hear your surgeon discuss how important it is to preserve these glands during surgery and avoid damage to them.

Function of the Thyroid

The thyroid primarily serves to regulate our body's metabolic rate. It accomplishes this task by producing the hormones thyroxine (T4), triiodothyronine (T3), and calcitonin. The thyroid uses iodine from our water and food intake to produce these hormones. Thyroid cells are unique because they are the only cells in the body that absorb iodine. This factor helps us to identify and eliminate thyroid cells in the body after cancer treatment by using a radioactive iodine scan and radioactive iodine therapy.

The thyroid is regulated by the pituitary gland, which is a tiny gland found in the base of the brain. The thyroid begins to produce T3 and T4 hormones when the pituitary releases a hormone called thyroid stimulating hormone (TSH). When thyroid levels begin to decrease in the body, the pituitary gland releases TSH, which prompt the thyroid to begin producing T3 and T4. T3 and T4 enter the bloodstream and circulate throughout the body, controlling cellular metabolic rate.

Ultimately, the pituitary gland is regulated by the hypothalamus in the brain. The hypothalamus releases thyrotropin releasing hormone (TRH), a hormone that tells the pituitary to produce TSH. It is a negative feedback system that sometimes does not properly function for various reasons, resulting in several possible thyroid diseases.

• Symptoms of Thyroid Disease
  
• Symptoms of Thyroid Cancer
  
• Thyroid Cancer 101

_Source:

_{American Cancer Society. Detailed Guide: Thyroid Cancer. How is Thyroid Cancer Diagnosed?. Revised 07/20/2010.}