Lymph Vessels function and blood
An extensive network of channels that collect and circulate LYMPH, a watery fluid containing immune cells and substances as well as pathogens cleansed from the BLOOD and tissues. The lymph vessels, also called lymphatics, are similar in structure to the capillaries and veins of the cardiovascular system but have thinner walls. The lymph vessels carry lymph from the tissues through the lymph nodes, where lymphocytes neutralize or kill and macrophages consume pathogens, then deliver the cleansed fluid to the blood.
The smallest of the lymph vessels are the lymphatic capillaries, which arise from cul-de-sac structures within the interstitial fluid (fluid between the cells) in the tissues surrounding the CAPILLARY BEDS of the cardiovascular system. The shingled, single-cell walls of the lymphatic capillaries are permeable, allowing fluid to seep inside though preventing it from seeping back out. The lymphatic capillaries merge into the afferent lymphatics, somewhat larger lymph vessels that carry the lymph among the lymph nodes. The lymphatic capillaries in the SMALL INTESTINE, called lacteals, are uniquely able to absorb the fatty products of digestion, which they ultimately deliver to the blood.
The larger lymph vessels are not permeable and contain valves to keep lymph moving in only one direction, toward the central body. Their pathways roughly parallel those of the cardiovascular circulatory structures. In the central trunk region the lymph vessels merge into three reservoir-like structures. These structures are the
- CISTERNA CHYLI, which collects lymph from the lacteals and the abdominal lymph vessels
- THORACIC DUCT, which collects lymph from the cisterna chyli and the upper left body
- RIGHT LYMPHATIC DUCT, which collects lymph from the upper right body and head
The thoracic duct parallels the AORTA and drains into the left subclavian vein. The right lymphatic duct drains into the right subclavian vein. The lymph then becomes part of the blood.
For further discussion of lymph vessels within the context of blood and lymph structure and function please see the overview section “The Blood and Lymph.”