Which statement about lymphatic capillaries is true?

• A. They lack endothelial cells
• B. They pump lymph by themselves
• C. Overlapping endothelial cells function as one-way valves
• D. They transport plasma within arteries

Answer: (C)

Lymphatic capillaries are lined by endothelial cells whose edges overlap to form tiny flap-like valves. These overlapping junctions create a one-way entry system: when interstitial fluid pressure rises, the flaps open to let fluid and tiny particles into the capillary, and they tend to close to prevent backflow, so the lymph moves in only one direction. This setup is aided by anchoring filaments that tether the capillaries to surrounding tissue, allowing the openings to widen with tissue swelling and increasing uptake during inflammation or edema. Lymph movement beyond the capillaries is driven by larger lymphatic vessels that have their own valves and muscle contractions; the capillaries themselves don’t pump lymph. They also don’t transport plasma within arteries—the plasma in arteries is separate from lymph.