Illustration of an enlarged and inflamed thyroid gland (goitre), caused by the autoimmune disorder thyroiditis, or Hashimoto's disease. The thyroid is an endocrine gland found in the neck, responsible for the production of hormones controlling the body's metabolism. When Hashimoto's disease occurs, the patient's immune system attacks the thyroid gland, causing hypothyroidism (lowered thyroid function). Treatment involves the use of levothyroxine, a synthetic thyroid hormone.