Melatonin: The Sleep Hormone

Definition and Function:
- Melatonin is a non-steroidal hormone secreted by the pineal gland.
- Its primary function is to regulate sleep and circadian rhythms, including growth and the menstrual cycle.
Production and Secretion:
- Site:
- Melatonin is secreted by the pineal gland, located on the posterior epithalamus.
- Control Mechanism:
- The release of melatonin is under nervous control.
- The process can be outlined as follows:
  - Darkness → SCN (Suprachiasmatic Nucleus) → Pineal Gland → Increased Melatonin Levels.
- Diurnal Cycle:
- Melatonin production follows a diurnal cycle, meaning levels rise and fall in accordance with the day-night cycle.
Impact on Other Hormones:
- Melatonin influences various biological processes, including:
- Growth hormone levels
- Cortisol levels
Regulation:
- Melatonin operates under a negative feedback control system. This means that the presence of certain light conditions can inhibit melatonin production.
- Suppression of Melatonin:
  - Dim light conditions, such as those encountered when pupils are dilated (e.g., when using televisions or devices), can suppress melatonin release, impacting the ability to sleep.
Illustrations:
- Figure 1: Diagram depicting the secretion of melatonin and its regulation by the SCN.
- Figure 2: Graph showing the diurnal cycle of melatonin production.
- Figure 3: Illustration demonstrating the impact of melatonin on growth hormone and cortisol levels.