Final answer:
Contraction of skeletal muscles external to the lymphatic vessels helps force lymph toward the lymphatic ducts. The lymphatic system employs a series of one-way valves to prevent backflow and relies on skeletal muscle contractions and vessel contractions to move lymph back into the circulatory system.
Step-by-step explanation:
Contraction of skeletal muscles external to the lymphatic vessels forces lymph toward the lymphatic ducts. Lymph movement is facilitated by both the contraction of the muscles surrounding the lymph vessels and the contractions of the lymph vessels themselves. The presence of one-way valves, such as semi-lunar valves, in lymphatic vessels ensures that lymph moves in the right direction, toward the heart, preventing backflow. Lymph flows from lymphatic capillaries, through larger lymphatic vessels, known as trunks, and eventually into the circulatory system via the lymphatic ducts. These ducts are located at the junction of the jugular and subclavian veins in the neck, which allows the lymph to return to the bloodstream.