Thyroid function is mainly regulated by two glands, the hypothalamus and the pituitary gland, and we will discuss the role of the hypothalamus in regulating thyroid function. The hypothalamus has supraoptic and paraventricular nuclei, which synthesize and secrete thyrotropin-releasing hormone, or TRH, from neuronal cells in the supraoptic and paraventricular nuclei. After stimulation, the pituitary gland synthesizes thyrotropin and secretes the synthesized thyrotropin in pulses, on average, every 1.8 hours. This pulsatile secretion of thyroid stimulating hormone has a circadian rhythm, usually peaking between 0:00 p.m. and 4:00 a.m. In hypothyroidism, the secretion of thyroid stimulating hormone and the pulsatile nighttime secretion peak are significantly higher than normal, whereas in hyperthyroidism, the opposite is true, that is, the secretion of thyroid stimulating hormone and the nighttime pulsatile secretion peak are significantly lower than normal, that is, the thyroid stimulating hormone secreted by it is reduced, which is clinically useful for identifying This is clinically significant for differentiating primary hyperthyroidism and primary hypothyroidism.