Which of the following hormones control 24 - hour diurnal cycle or rhythmic activity of human body ?

Options

A. Thymosin
B. Melanin
C. Melatonin
D. Thyroxine

Answer

To solve the question "Which of the following hormones control 24-hour diurnal cycle or rhythmic activity of the human body?", we will analyze the given options step by step.

### Step 1: Understand the Concept of Diurnal Cycle
- The diurnal cycle refers to the 24-hour cycle that includes the alternation of day and night. It is closely related to the sleep-wake cycle and other rhythmic activities in the human body.

**Hint:** Think about how our bodies respond to light and darkness throughout the day.

### Step 2: Analyze the Given Hormones
We have four options to consider:
1. **Thymosine**
2. **Melanin**
3. **Melatonin**
4. **Thyroxine**

**Hint:** Consider the function of each hormone and which one is related to sleep and circadian rhythms.

### Step 3: Evaluate Each Hormone
1. **Thymosine**:
- Secreted by the thymus gland, it plays a role in the immune system. It is not involved in regulating the diurnal cycle.

**Hint:** Focus on the role of thymosine in immunity.

2. **Melanin**:
- A pigment responsible for skin color. It does not have a role in regulating the diurnal cycle.

**Hint:** Remember that melanin is related to pigmentation, not hormonal regulation.

3. **Melatonin**:
- Secreted by the pineal gland, melatonin is known to regulate sleep-wake cycles and is directly involved in the diurnal rhythm of the human body.

**Hint:** Think about how melatonin levels change with light exposure and its effect on sleep.

4. **Thyroxine**:
- Produced by the thyroid gland, thyroxine regulates metabolism but does not control the diurnal cycle.

**Hint:** Consider the metabolic functions of thyroxine rather than sleep regulation.

### Step 4: Conclusion
Based on the analysis, the hormone that controls the 24-hour diurnal cycle or rhythmic activity of the human body is **melatonin**.

### Final Answer:
**Melatonin** is the correct answer.

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