It is an extensive network of thin-walled vessels that arise as blind-ended lymph capillaries in most of the tissues of the body. The lymph capillaries unite to form a tree like structure of increasingly larger lymph vessels, which finally drain lymph into veins in the lower neck region. Lymphatic system is an open circulatory system.
• Lymph capillaries are microscopic, closed-ended tubes that form vast network in the intercellular spaces. The walls are composed of endothelial cells, with porous junctions, through which interstitial fluid/ extracellular fluid (ECF), proteins, microorganisms and absorbed fats can easily enter. Once the extra cellular fluid enters from the lymphatic capillaries, it is referred to the as lymph.
• The lymph capillaries merge and form large, lymphatic vessels which lead into larger lymph ducts. The walls of the lymph vessels and ducts are similar to those of veins and are provided with valves. The smooth muscles of their walls cause peristaltic waves of contraction pushing lymph towards the neck region.
All the lymph vessels from the lower part of the body eventually empty lymph into the thoracic duct. The thoracic duct of the lymphatic system is the largest lymphatic vessel (lymph duct) in the body. It is also known as the left lymphatic duct, chyliferous duct etc., and it empties the lymph into the venous system at the junction of the left internal jugular vein and left subclavian vein. Lymph collected from the left side of the head, the left arm, and the parts of the chest region also enters the thoracic duct before it empties into the venous system. Lymph from the right side of the neck, head, right arm, and the right part of the thorax is collected into the right lymphatic duct which empties it into venous system at the junction of the right sub clavian vein and internal jugular vein.
