What characteristic does the lymphatic vessel endothelial lining have?

The lymphatic vessel endothelial lining is characterized by a "flap valve" mechanism, which is crucial for its function. This structure allows the endothelial cells that make up the walls of lymphatic vessels to overlap and create flaps. These flaps open when interstitial fluid pressure rises, allowing excess fluid, proteins, and larger particles to enter the lymphatic system. Conversely, when the pressure inside the vessel is higher than that in the surrounding tissue, the flaps close to prevent backflow. This unique structure is vital for maintaining the unidirectional flow of lymph and the regulation of fluid balance in the body.

While other options may not describe the characteristics of lymphatic vessels accurately, it is essential to understand that the "flap valve" mechanism is what differentiates the lymphatic system from other vascular systems, allowing for the effective collection and transport of lymph.