The 24 hour (diurnal) rhythm of our body such as the sleep-wake cycle is regulated by the hormone
Or
Which hormone is secreted more in dark condition

Options

A. Calcitonin
B. Prolactin
C. Adrenaline
D. Melatonin

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the hormone that regulates the 24-hour rhythm of our body, specifically the sleep-wake cycle, and which hormone is secreted more in dark conditions.

2. **Identifying the Relevant Gland**: The gland responsible for regulating the sleep-wake cycle is the pineal gland. This gland is located in the brain and plays a crucial role in the production of certain hormones.

3. **Identifying the Hormone**: The primary hormone secreted by the pineal gland is melatonin. Melatonin is known for its role in regulating sleep patterns and circadian rhythms.

4. **Understanding Melatonin's Function**: Melatonin levels increase in response to darkness, signaling the body that it is time to sleep. This hormone helps to induce sleep and regulate the sleep-wake cycle.

5. **Eliminating Other Options**:
- **Calcitonin**: This hormone is secreted by the thyroid gland and is involved in calcium regulation, not sleep.
- **Prolactin**: This hormone is involved in milk production and does not play a role in sleep regulation.
- **Adrenaline**: This hormone is associated with the fight-or-flight response and is not related to sleep.

6. **Conclusion**: Based on the information gathered, the hormone that regulates the sleep-wake cycle and is secreted more in dark conditions is **melatonin**.

### Final Answer:
The hormone that regulates the 24-hour rhythm of our body, such as the sleep-wake cycle, and is secreted more in dark conditions is **melatonin**.

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