Thoracic duct opens into

Options

A. Right subclavian artery
B. Left subclavian artery
C. Right subclavian vein
D. Left subclavian vein

Answer

**Step-by-Step Solution:**

1. **Understanding the Thoracic Duct**: The thoracic duct is the largest lymphatic duct in the human body. It plays a crucial role in the lymphatic system by transporting lymph, which is a fluid containing infection-fighting white blood cells, throughout the body.

2. **Function of the Thoracic Duct**: The thoracic duct collects lymph from approximately 75% of the body, including the left side of the head, neck, chest, left arm, and the entire lower body. It is essential for maintaining fluid balance and immune function.

3. **Location of the Opening**: The thoracic duct typically opens into a specific vein. The options provided in the question include:
- Right subclavian artery
- Left subclavian artery
- Right subclavian vein
- Left subclavian vein

4. **Identifying the Correct Opening**: The thoracic duct opens into the left subclavian vein. This is an important anatomical feature as it allows the lymph to re-enter the circulatory system.

5. **Pathway to the Heart**: Once the lymph enters the left subclavian vein, it eventually flows into the superior vena cava (or inferior vena cava), which then leads to the heart. This is crucial for the return of lymphatic fluid to the bloodstream.

6. **Conclusion**: Therefore, the thoracic duct opens into the left subclavian vein.

**Final Answer**: The thoracic duct opens into the **left subclavian vein**.

---