Endocrine glands release hormones (chemical messengers) into the bloodstream to be transported to various organs and tissues throughout the body. For instance, the pancreas secretes insulin, which allows the body to regulate levels of sugar in the blood. The thyroid gets instructions from the pituitary to secrete hormones which determine the pace of chemical activity in the body (the more hormone in the bloodstream, the faster the chemical activity; the less hormone, the slower the activity).

This image shows enlargement of the thyroid gland and extension down behind the breastbone (retrosternal space). The image, called a scintiscan, was generated using a radioactive isotope.

Graves disease is an autoimmune disorder that involves overactivity of the thyroid gland (hyperthyroidism). Hallmarks of the condition are bulging eyes (exophthalmos), heat intolerance, increased energy, difficulty sleeping, diarrhea, and anxiety.

The thyroid gland, a part of the endocrine (hormone) system, plays a major role in regulating the body's metabolism.