The correct option is 1, 2 and 3 only.
Explanation
Melatonin is a hormone secreted by the pineal gland, a small endocrine gland located on the dorsal side of the forebrain. It plays a critical role in the regulation of the 24-hour (diurnal) rhythm of the body.
Statement-wise Analysis
- Statement 1 is Correct: Melatonin is the primary hormone responsible for regulating the body's internal clock. It maintains the normal rhythms of the sleep-wake cycle (circadian rhythm).
- Statement 2 is Correct: Along with the sleep-wake cycle, melatonin helps regulate body temperature, typically lowering it during sleep to facilitate rest.
- Statement 3 is Correct: Melatonin influences metabolism and pigmentation. In many vertebrates, it affects skin coloration (pigmentation), and in mammals, it plays a role in metabolic processes.
- Statement 4 is Incorrect: Melatonin does influence the menstrual cycle. Additionally, it plays a role in the body's defense capability (immunity).
Key Takeaway
Melatonin, secreted by the pineal gland, regulates the diurnal rhythm (sleep-wake cycle), body temperature, metabolism, pigmentation, the menstrual cycle, and defense capabilities.