An inadequate secretion of thyroid hormones results in , which is characterized by weight gain and lethargy, while an excess of thyroid hormone secretion results in , which is characterized by weight loss and rapid pulse.

hypothyroidism, hyperthyroidism

Explanation: Thyroid is a small gland with the shape of a butterfly located in the lower neck that controls the body's metabolism by secreting two hormones: thyroxine (T4) and iodothyronine (T3). A well functioning thyroid secretes the right quantity of hormones that are needed to maintain the normal body metabolism. When the thyroid malfunctions, it results in a thyroid disease. Hypothyroidism is a thyroid disease that results from the undersecretion of thyroid hormones by the thyroid gland while hyperthyroidism is a thyroid disease resulting from the oversecretion of thyroid hormones by the thyroid gland. Hypothyroidism results from an interactive thyroid gland and it is characterized by weight gain and lethargy while hyperthyroidism results from overactive thyroid gland and it is characterized by weight loss and increase metabolism.