Answer: The body's circadian rhythm and sleep-wake cycle.
- A The body's circadian rhythm and sleep-wake cycle
- B Basal metabolic rate of body tissues in standard reference material
- C Water reabsorption in the kidney tubules as widely reported
- D Blood glucose levels following meals in the majority of documented cases
Correct answer: A. The body's circadian rhythm and sleep-wake cycle
Explanation: Melatonin secretion follows a light-dependent rhythm and helps regulate circadian rhythms, including the timing of the sleep-wake cycle.
The hypothalamus releases hormones that direct the pituitary, which releases its own trophic hormone to a target gland; that gland's hormone output then feeds back (dashed lines) to suppress both the pituitary and hypothalamus once levels are sufficient - a self-correcting loop running the entire endocrine system.
Concept context
The endocrine glands, hormone classification and mechanism of action, and negative feedback regulation.