How does the structure of lymphatic capillaries correlate with their function?

Intelligent design: The fluid carried by the blood stream/arteries leaks out into the tissues through the capillary walls and when the tissues are healthy, are drawn into the minute lymph channels and flows back into the blood stream at the superior vena cava just above the heart before the blood goes through the lungs for re-oxygenation. Impairment of the delicate channels or lymph nodes results in edema.

Intelligent Design 2: Dr. Barton's answer is excellent. All of flow through your arteries, veins and lymphatics depends on pressure differences between the three to keep the system operating properly all the time. The higher pressure in arterial capillaries allows blood cells to travel into lower pressure venous capillaries. At the same time, lower tissue pressure allows lymph to leave arteries and not go into veins.