Question

Melatonin is secreted by:

• A. Thyrotrophs
• B. Gonadotrophs
• C. Pineal gland
• D. Adrenal gland

Hint:

The pineal gland is the primary source of melatonin, a hormone crucial for regulating the circadian rhythm. Its secretion increases in response to darkness.

Answer 1

The Correct Option is C

Step 1: Understanding melatonin secretion. Melatonin is a hormone primarily secreted by the pineal gland, a small endocrine gland located in the brain. 

Step 2: Role of melatonin. Melatonin regulates the sleep-wake cycle (circadian rhythm) and is influenced by the light-dark cycle. Its secretion increases in darkness and decreases in light. 

Step 3: Why other options are incorrect. 
- (A) Thyrotrophs: These are cells in the anterior pituitary gland that secrete thyroid-stimulating hormone (TSH), not melatonin. 
- (B) Gonadotrophs: These are pituitary cells that secrete gonadotropins like LH and FSH. 
- (D) Adrenal gland: Secretes hormones like cortisol, aldosterone, and adrenaline, but not melatonin.

Answer 2

The question asks which gland secretes melatonin. Let's check what each of the four listed glands or cell types is actually known to produce.

1. Thyrotrophs: These are specialized cells in the anterior pituitary gland that secrete thyroid-stimulating hormone (TSH), which controls thyroid hormone output. They have no role in melatonin production.
2. Gonadotrophs: These are also anterior pituitary cells, but they secrete luteinizing hormone and follicle-stimulating hormone to regulate reproductive function. Melatonin is not among their products.
3. Pineal gland: The pineal gland, a small structure located deep in the brain, is the primary source of melatonin. Its secretion is directly tied to the light-dark cycle, rising in darkness and falling with light exposure, which lets melatonin regulate the sleep-wake cycle.
4. Adrenal gland: The adrenal gland secretes hormones like cortisol, aldosterone, and adrenaline, all involved in stress response, salt balance, and the fight-or-flight reaction. Melatonin is not one of its secretions.

Thyrotrophs, gonadotrophs, and the adrenal gland each secrete their own distinct set of hormones unrelated to sleep regulation, leaving the pineal gland as the actual source of melatonin.

So the correct answer is Pineal gland.