Final answer:
Lymph and venous blood flow depend on the transportation of lymph through lymphatic vessels and its eventual return to the venous bloodstream, a process facilitated by muscle actions and one-way valves.
Step-by-step explanation:
Both lymph and venous blood flow are reliant on movement processes that are not directly driven by heart pressure. The movement of lymph through the lymphatic system is essential for maintaining fluid balance and protecting the body from infection. As fluid leaks out from the capillaries into the interstitial spaces, it accumulates as interstitial fluid. A portion of this fluid enters the lymphatic system, becoming lymph. Lymph is then transported through the network of lymphatic vessels by the actions of smooth muscle contractions, the external pressure of skeletal muscles, and one-way valves that prevent backflow, eventually emptying into the venous bloodstream through the subclavian veins.
The lymphatic capillaries collect excess fluid and proteins that cannot leave the blood capillaries. This system of vessels ensures a one-directional flow from the periphery towards the heart. It also acts as a filtration system through lymph nodes, with white blood cells removing infectious agents from the lymph. The flow of lymph is facilitated by smooth muscle action, skeletal muscle contractions, and one-way valves, culminating in its return to the bloodstream via the vena cava.