The lymphatic system is made up of very fine capillaries that are next to the blood vessels. These merge into larger branches known as trunks, and these in turn merge into two larger vessels called ducts. The thoracic and right lymphatic ducts empty into the venous system in the region of the collarbones. Venous blood is blood returning to the heart. This means that it is deoxygenated. Lymph fluid runs into this type of blood, so any infection being carried in the lymphatic fluid would then go right into the heart.
Nodes and ducts also make up the lymphatic system. The lymph nodes, which are approximately one to two centimeters long produce the lymphatic fluid, which is made from the fluid and protein that has been extracted from of the blood (blood plasma). This lymph is then drained from the tissue in microscopic vessels called lymph capillaries.