What is the Origin of Term 13?

The term is rooted in neuroendocrinology and chronobiology, dating back to the identification of the pineal gland's function as a photosensitive organ in the 1950s. Melatonin's role as the "hormone of darkness" solidified its importance as a critical output signal of the master circadian clock in the suprachiasmatic nucleus (SCN). Understanding its rhythm is crucial for managing sleep disorders and optimizing hormonal timing.

What is the Mechanism of Term 13?

Melatonin synthesis and secretion are directly controlled by the SCN, which receives light input from the retina via the retinohypothalamic tract. When light levels diminish, the SCN disinhibits the sympathetic nervous system pathway leading to the pineal gland. This allows the rate-limiting enzyme, N-acetyltransferase, to become active, converting serotonin into N-acetylserotonin, which is then methylated to form melatonin for release into the systemic circulation.

Term 13 ∞ Area

Term 13

Meaning

Melatonin Secretion is the rhythmic, nightly release of the hormone melatonin, primarily from the pineal gland, which serves as the body’s key signal for darkness and the primary regulator of the sleep-wake cycle. This neurohormone is a potent antioxidant and plays a role in immune modulation and circadian rhythm synchronization across all peripheral organs. A healthy pattern of secretion is characterized by a rapid increase shortly after the onset of darkness, peaking in the middle of the night, and sharply declining toward morning. Disrupted secretion, often due to light exposure at night, is a common clinical issue leading to sleep disturbances and circadian misalignment.