Lymphatic system: Encyclopedia II - Lymphatic system - Lymphatic circulation

Lymphatic system - Lymphatic circulation

The lymphatic system acts as a secondary circulatory system. Unlike the circulatory system, the lymphatic system is not closed and has no central pump; the lymph moves slowly and under low pressure due mostly to the milking action of skeletal muscles. Like veins, lymph vessels have one-way valves and depend mainly on the movement of skeletal muscles to squeeze fluid through them. Rhythmic contraction of the vessel walls may also help draw fluid into the lymphatic capillaries. This fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); these ducts drain into the circulatory system at the right and left subclavian veins.

Lymph vessels are present in the lining of the gastrointestinal tract. Whilst most other nutrients absorbed by the small intestine are passed on to the portal venous system to drain, via the portal vein, into the liver for processing, fats are passed on to the lymphatic system, to be transported to the blood circulation via the thoracic duct. The enriched lymph originating in the lymphatics of the small intestine is called chyle. The nutrients that are released to the circulatory system are processed by the liver, having passed through the systemic circulation. The lymph system is a one-way system (interstitial fluid back to blood).

Adapted from the Wikipedia article "Lymphatic circulation", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki