Thyroid Gland Function: The pituitary gland in the brain secretes TSH, which stimulates the thyroid gland (located in the neck) to release thyroid hormones – primarily T3 (triiodothyronine) and T4 (thyroxine). Thyroid Disorders: There are two major types – Hypothyroidism and Hyperthyroidism. Hypothyroidism: This is the more common condition. It occurs when the thyroid gland secretes less thyroid hormone (T3 & T4) than required. Hyperthyroidism: The hormone production is excessive, and TSH levels decrease. Signs, Symptoms, and Treatment: Each condition has distinct signs and symptoms, and treatments are available depending on the specific diagnosis.