Which of the following is not a method that maintains lymph flow?

a. capillary smooth muscle contraction
b. skeletal muscle contraction
c. valves in lymph vessel walls
d. breathing

The correct answer is: D. breathing

Lymphatic system is an open system that does not have a central pump (such as heart in the circulatory system), so the flow of the lymph is different than blood flow. Transport and movement of the lymph are slow and sporadic. Lymph flow occurs thanks to:  

•peristalsis – contraction and relaxation smooth muscle tissue,  

•valves- so that lymph doesn’t flow backwards along the vessels

•contraction of adjacent skeletal muscle .