Lymphatic System

The lymphatic system and immunity

Lymphatic SystemThe lymphatic system mediates our immunity. It is comparable in the complexity of its functions to the nervous system: both systems operate through multiple organs dispersed through most of the body’s tissues.

The average immune system in a man weighs two pounds and consists of a trillion cells (lymphocytes) and 100 million trillion molecules (antibodies) produced and secreted by the lymphocytes.

Lymphocytes and antibodies circulate through the body via the bloodstream, passing through capillary walls to enter tissues where they identify and destroy cells identified as foreign, such as cancer cells, bacteria, and viruses.

After their work is done, lymphocytes and antibodies enter their own vascular network, the lymphatic system. The vessels of the lymphatic system collect lymphocytes, antibodies, large protein molecules, fat molecules and approximately three liters of the fluid (interstitial fluid) that bathes all the cells in the body.

This load of cells and fluid passes through a series of lymph nodes which filter out pathogens, cell debris and excess water. The concentrated lymph then continues its journey to the two major ducts located behind the collar bones where it re enters the circulatory system via the subclavian veins.

Lymphocytes form and are stored in the lymph nodes, pea sized glands located in large numbers in the abdomen, groin, armpits and neck. Other lymphatic tissues are the tonsils, the spleen, and specialized lymphoid tissues in the intestines.

 

The lymphatic system and fluid balance

The circulatory system and the lymphatic system work together to regulate the fluid balance throughout the body. Plasma moves out of the capillaries into the tissues to bathe the cells, bringing nutrients and oxygen and removing waste products. Once outside of the capillary wall the plasma is called interstitial fluid. Interstitial fluid that enters a lymphatic vessel is called lymph.

Until recently it was believed that 90% of the interstitial fluid returned to the circulatory system via the venous capillaries, and only 10%  was taken up by the lymph vessels.  Recent studies have shown just the reverse: approximately 90% of the interstitial fluid (2 to 3 liters) is carried by the lymphatic vessels to be returned to the circulatory system.
 

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