Sleep hormones are a collective term for the key endocrine signaling molecules that regulate the initiation, maintenance, and architecture of the sleep-wake cycle and whose secretion is tightly controlled by the circadian rhythm. The primary examples include melatonin, which signals darkness and promotes sleep propensity, and cortisol, whose awakening response promotes arousal. Other crucial regulators are Growth Hormone and Prolactin, which are released during specific sleep stages to support cellular repair and immune function. The coordinated rhythm of these hormones is essential for restorative sleep.
Origin
The identification of hormones that regulate sleep began with the discovery of melatonin in the pineal gland and the subsequent understanding of its role as a darkness signal. The concept evolved as endocrinologists mapped the pulsatile release of other systemic hormones, confirming their dependence on the sleep state. The term is a functional classification within the broader discipline of neuroendocrinology.
Mechanism
Melatonin acts on receptors in the SCN to reinforce the nocturnal phase of the circadian clock, reducing core body temperature and increasing the drive for sleep. Cortisol secretion is suppressed during the deep sleep phase but surges pre-waking to prepare the body for metabolic activity. The reciprocal relationship between these hormones and the sleep stages ensures that the body’s major anabolic and catabolic processes are appropriately timed for optimal physiological restoration and daytime function.
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