The pineal gland is a small bean-shaped body located between the mesencephalon and the thalamus, which is connected to the roof of the third ventricle and is mainly composed of pineal cells, glial cells, and nerve fibers. It can play a role in regulating our neurosecretory and reproductive systems, and can significantly control our emotions and moods, which are influenced by the pineal gland in humans. Its regulation accepts circadian rhythms, while it is able to influence and intervene in a variety of human neurological functions through the secretion of hormones that affect our sleep and wakefulness. The biological cycle effect and the influence of light can also affect the function of the pineal gland. The pineal gland also indirectly controls the functions of our nervous system, endocrine system, and immune system. Melatonin secreted by the pineal gland can inhibit the secretion of gonadotropins and thus inhibit gonadal activity and sexual maturation.