Thyroid hormones play an important role in the regulation of the basal metabolic rate and also influence the maintenance of water and electrolyte balance , . The normal rhythm of the sleep-wake cycle is regulated by melatonin secreted by the pineal gland . The development of the immune system is a major role of the thymus gland and its hormones, thymosins , . Therefore, statements C and D describe functions not under the control of the thyroid hormone.