Lymph and Lymph Node Circulation

Lymphatic vessels, known as lymphatics, transport a watery fluid called lymph from body tissues, filter it through lymph nodes, and return it to the bloodstream. Blood capillaries filter fluid containing water, oxygen, and nutrients into the tissues to form interstitial fluid. Most of this fluid, along with cellular wastes, is reabsorbed into the bloodstream by capillaries.

Lymphatic capillaries drain excess extracellular materials, maintaining fluid balance and immunity. Their loose endothelial junctions allow macromolecules and pathogens to enter the lymph circulation. These capillaries converge into collecting vessels, along which lymph nodes are located. Inside a lymph node, sinuses connect the cortex and medulla, where immune cells like lymphocytes, macrophages, and other antigen-presenting cells filter the lymph, destroying pathogens and harmful cells or preparing an immune response.

After filtration, cleansed lymph, primarily composed of water, protein, and lymphocytes, exits the node via efferent collecting vessels. Vessel wall contractions push lymph through valves, preventing backflow. These collecting vessels combine into lymphatic trunks that drain specific body regions. These trunks empty into either the right lymphatic duct, which processes lymph from the right side of the head, right arm, and right thorax, or the thoracic duct, which handles lymph from the rest of the body. Both ducts return lymph to the subclavian veins, reintroducing it to the bloodstream.