AP BIOLOGY

Detailed explanation-1: -There is no pump in the lymphatic system like the heart in the cardiovascular system. The pressure gradients to move lymph through the vessels come from the skeletal muscle action, respiratory movement, and contraction of smooth muscle in vessel walls.

Detailed explanation-2: -The lymphatic system is an active pumping system driven by segments that have a function similar to peristalsis. They lack a central pump (like the heart in the cardio vascular system), so smooth muscle tissue contracts to move lymph along through the vessels.

Detailed explanation-3: -Accordingly, when the muscle contracts, the lymphatics collapse and propel fluid forward, with the valvular structure of the lymphatic capillaries allowing only unidirectional flow of lymph (Skalak et al. 1984).