Lymphatic Vessels

Extracellular fluid circulates back to the vascular system through lymphatic vessels. Extracellular fluid enters lymphatic vessels through closed-ended lymphatic capillaries. Lymphatic capillaries consist of simple squamous epithelium and are highly permeable.

Fluid movement in lymphatic vessels is driven primarily by skeletal muscle contraction. Valves in lymphatic vessels ensure one-way flow in a low pressure system. As lymph is carried back to the veins, it passes through lymph nodes to remove foreign invaders.