Final answer:
Lymph from the left arm enters the venous circulation through the thoracic duct, which drains into the left subclavian vein.
Step-by-step explanation:
Lymph traveling from the left arm would enter the venous circulation via the thoracic duct. The thoracic duct is a large lymphatic duct that is responsible for draining lymph from the lower limbs, the left thorax, the left upper limb, and the left side of the head. This duct begins at the cisterna chyli and ultimately drains into the left subclavian vein. In contrast, the right lymphatic duct drains lymph from the upper right portion of the body, which includes the right side of the head, thorax, and right upper limb, into the right subclavian vein. Understanding this organization of the lymphatic system is crucial for the organization of immune function and proper lymphatic drainage.
Given this information, the student's question regarding where lymph from the left arm enters the bloodstream can be confidently answered as the thoracic duct. This is because the thoracic duct drains lymph from the entire left side of the body and the lower parts of the right side.