Lymphatic Anatomy

Lymphatic vessels use one-directional valves to move lymph only toward the heart. Lymphatic capillaries are small vessels beneath the skin with highly permeable endothelial walls. The permeability of lymphatic capillaries allows large molecules and immune cells to enter the lymphatic system from tissues. Lymph nodes trap pathogens in lymph fluid and resident immune cells destroy them. The spleen, thymus, tonsils, and bone marrow contribute to white blood cell production and immune function. Most lymph drains through the thoracic duct into the left subclavian vein near the collarbone.