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Which cells make melatonin, and what shuts its production down?
APinealocytes, shut down by bright light
BPinealocytes, shut down by falling light
CMelanocytes, shut down by bright light
DRetinal cells, shut down by darkness
Answer & Solution
Correct answer: A. Pinealocytes, shut down by bright light
1. Melatonin is an amine hormone derived from serotonin and made by the pinealocytes of the pineal gland.
2. Light striking the retina sends an impulse to the suprachiasmatic nucleus of the hypothalamus.
3. That signal travels on to the pineal gland, where melatonin production is inhibited and blood levels fall, promoting wakefulness.
4. Falling light does the reverse and raises melatonin, and melanocytes make skin pigment rather than any hormone of sleep.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 17 "The Endocrine System", section 17.7 The Pineal Gland_
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