Sleep wake cycle regulated by

The correct answer is Melatonin (pineal gland)

Explanation:

• The sleep-wake cycle, also known as the circadian rhythm, is a natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours. It is influenced by various factors, but the primary regulator is the hormone melatonin, which is produced by the pineal gland in the brain.
• Melatonin is often referred to as the "sleep hormone" because it is responsible for signaling the body to prepare for sleep as it gets dark outside.
• Melatonin also influences metabolism, pigmentation, the menstrual cycle as well as our defense capability.

Other Options:

• Growth Hormone (GH) (pituitary gland): GH is produced by the pituitary gland and primarily stimulates growth, cell reproduction, and cell regeneration. It plays an important role in human development.
• Adrenaline (adrenal gland): Adrenaline, also known as epinephrine, is a hormone and neurotransmitter produced by the adrenal glands. It is part of the body's fight-or-flight response and prepares the body for a quick reaction in stressful situations. Adrenaline increases heart rate, muscle strength, blood pressure, and sugar metabolism.
• Thyroxin (thyroid gland): Thyroxin, or T4, is a hormone produced by the thyroid gland. It regulates metabolism, heart rate, and growth and development.