10.4. Lymphatic System
The lymphatic system has three main roles:
- To collect excess fluid and proteins from tissues and return these to the blood in the form of lymph;
- To transport fats from the small intestine into the blood via lacteals;
- To support immunity by destroying microorganisms.
The Main Lymphatic Vessels
There are two main lymphatic vessels in the body. These are called the right lymphatic duct and the thoracic duct. Their job is to drain their lymph fluid back into the systemic circulation. The right lymphatic duct drains the upper right side of the body (specifically, the right side of the head and neck, right arm and right axilla - and that is all). The thoracic duct drains lymph from the rest of the body. It begins as the cisterna chyli, an enlarged sac of lymph in the upper abdomen, close to the stomach. This can be seen in the diagram. This sac receives all of the lymph from the abdominal and pelvic cavities and the lower limbs. It then narrows and ascends, as the thoracic duct, through the aortic hiatus (which we said in Section 2.8. runs behind the diaphragm at the level of T12). The thoracic duct gradually veers left until it reaches the root of the neck, at which point it curves 180o back down and empties into the left brachiocephalic vein. While in the root of the neck, it actually receives other lymph vessels from the left side of the head and neck, left upper arm and left axilla. As said, this lymph is all returned into the venous system.