The thyroid gland is a butterfly-shaped gland in the front of
the neck. Hypothyroidism is a condition in which the thyroid
gland does not produce enough thyroid hormones. A healthy
thyroid produces the hormones thyroxine (T4) and
triiodothyronine (T3), which control metabolism. This affects
how many calories you burn, how warm you feel, how much you
weigh, and how the body handles functions of the cardiovascular,
gastrointestinal, and nervous systems. Hypothyroidism results in
a slower metabolism and a slower heartbeat. Hashimoto's
thyroiditis occurs when the immune system produces antibodies
that attack cells of the thyroid gland. This results in thyroid
swelling. Other less common causes include hypothyroidism as a
result of neck radiation for lymphoma and treatment of
hyperthyroidism or thyroid cancer with radioactive iodine or
surgery. Other causes of hypothyroidism include: - Subacute
thyroiditis —This occurs when there is inflammation of the
thyroid gland after a viral upper respiratory tract infection.