Lymphatic System 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 , proteins, microorganisms and absorbed fats can easily enter. once the extra cellular fluid enters the lymphatic capillaries, it is referred to as lymph  click here for complete lecture