Hormone regulating diurnal rhythm/sleep wake cycle is

Options

A. Thymosin
B. Glucagon
C. Melatonin
D. Oxytocin.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks for the hormone that regulates the diurnal rhythm or sleep-wake cycle. This means we need to identify which hormone is responsible for controlling our sleep patterns and daily biological rhythms.

2. **Analyzing the Options:**
We have four options to consider: thymosin, glucagon, melatonin, and oxytocin.

3. **Evaluating Thymosin:**
- Thymosin is secreted by the thymus gland.
- Its primary function is to stimulate T cells, which are crucial for the immune response.
- Since thymosin is involved in immunity and not in regulating sleep, this option is incorrect.

4. **Evaluating Glucagon:**
- Glucagon is a hormone produced by the pancreas.
- It functions to increase blood glucose levels, counteracting the effects of insulin.
- Glucagon is related to metabolism and energy balance, not to sleep regulation, making this option incorrect as well.

5. **Evaluating Melatonin:**
- Melatonin is often referred to as the "sleep hormone."
- It is produced by the pineal gland in response to darkness and helps regulate the sleep-wake cycle.
- Melatonin plays a vital role in maintaining the body's internal clock and diurnal rhythms, making this the correct choice.

6. **Evaluating Oxytocin:**
- Oxytocin is produced by the posterior pituitary gland.
- It is primarily known for its role in childbirth and lactation, as it stimulates uterine contractions and milk ejection.
- Since oxytocin does not have a role in regulating sleep or diurnal rhythms, this option is also incorrect.

7. **Conclusion:**
After evaluating all the options, the hormone that regulates the diurnal rhythm or sleep-wake cycle is **melatonin**.

---