Hormone named Melatonin which is associated with the diurnal rhythms of the body is secreted by

Options

A. skin
B. thymus
C. pituitary
D. pineal gland

Explanation

**Step-by-Step Solution:**

1. **Identify the Hormone**: The hormone in question is Melatonin, which is known to be associated with the diurnal rhythms of the body.

2. **Locate the Gland**: Melatonin is secreted by the pineal gland. The pineal gland is a small gland located in the brain, specifically between the cerebral hemispheres and protruding from the roof of the third ventricle.

3. **Understand the Function**: Melatonin plays a crucial role in regulating sleep patterns and is often referred to as the "sleep hormone." Its secretion is influenced by light; it increases in dim light and decreases in bright light.

4. **Diurnal Rhythm**: The concentration of melatonin in the blood follows a diurnal rhythm, meaning it varies throughout the day and night, helping to regulate the body's internal clock.

5. **Additional Functions**: Besides regulating sleep, melatonin also has roles in skin pigmentation in some animals, immune defense regulation, and menstrual cycle regulation.

6. **Conclusion**: Based on the information gathered, the correct answer to the question is that melatonin is secreted by the pineal gland.

**Final Answer**: Melatonin is secreted by the pineal gland.

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