Where does the thoracic duct empty into the circulatory system?

The thoracic duct is a crucial component of the lymphatic system, responsible for draining lymph fluid from the lower body, left side of the head, neck, arms, and most of the thorax into the circulatory system. It empties at the junction of the left internal jugular vein and the left subclavian vein, forming what is commonly referred to as the venous angle.

This location is significant as it allows for the re-entry of lymph into the bloodstream at a point where it can quickly circulate throughout the body, effectively maintaining fluid balance and immune function. Proper understanding of the drainage pathways of the thoracic duct is essential for comprehending lymphatic flow and its interactions with the vascular system. Thus, the junction of the left internal jugular and the left subclavian vein is the correct answer, emphasizing the thoracic duct's vital role in connecting the lymphatic system to the bloodstream.