Final answer:
Lymph is moved through the lymphatic vessels by the contraction of skeletal muscles, aided by the vessel's own contractions and one-way valves that prevent backflow. The lymphatic system does not have a central pump like the heart in the cardiovascular system.
Step-by-step explanation:
The muscle that moves lymph through the lymphatic vessels and prevents it from flowing backward is the skeletal muscle. Unlike the cardiovascular system where the heart pumps blood, the lymphatic system relies on the contraction of skeletal muscles during body movements and breathing to help propel lymph. This mechanism is aided by one-way valves known as semi-lunar valves, which ensure that lymph moves in the direction toward the heart.
In addition to muscular contractions, lymphatic vessels themselves contract periodically to facilitate lymph movement. Lymph flows from the lymphatic capillaries, through the vessels, and is eventually returned to the circulatory system through lymphatic ducts at the junction of the jugular and subclavian veins.
Lymphatic vessels are crucial for the transportation of lymph fluid, which contains immune cells and is essential for removing excess fluid from tissue spaces. The lymphatic system is also involved in filtering pathogens at lymph nodes and transporting immune cells and dietary lipids.