View source for Lymph vascular system

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==Overview==
[[Image:Illu lymphatic system.jpg|thumb|250px|right]]
The '''lymphatic system''' is a complex network of lymphoid organs, [[lymph node]]s, [[Thoracic duct|lymph ducts]], [[lymphatic tissues]], [[lymph capillaries]] and [[lymph vessel]]s that produce and transport lymph fluid from [[Biological tissue|tissue]]s to the [[circulatory system]]. The lymphatic system is a major part of the [[immune system]].

The lymphatic system has three interrelated functions: (1) removal of excess fluids from body tissues, (2) absorption of fatty acids and subsequent transport of fat, as [[chyle]], to the circulatory system, and (3) production of immune cells such as [[lymphocyte]]s (e.g. antibody producing [[plasma cell]]s) and [[monocyte]]s. <ref> http://www.lymphomation.org/lymphatic.htm </ref>

==Discovery==
[[Olaus Rudbeck]] the Elder of Sweden (1630–1702) was a university dean, natural scientist, archaeologist and more. In 1652 he discovered the lymphatic system. He pointed to these as the source of production of white blood cells.

==Lymphatic circulation==
Unlike the cardiovascular system, the lymphatic system is not closed and has no central pump.  Lymph movement occurs  with low pressure due to [[peristalsis]], valves, and the milking action of skeletal muscles. Like [[vein]]s, lymph travels through vessels in one way only, due to [[semilunar valves]].  This depends mainly on the movement of skeletal muscles to squeeze fluid through them, especially near the joints.  Rhythmic contraction of the vessel walls through movements may also help draw fluid into the smallest lymphatic vessels, [[capillary|capillaries]]. Tight clothing can restrict this, thus reducing the removal of wastes and allowing them to accumulate. If tissue fluid builds up the tissue will swell; this is called [[edema]]. As the circular path through the body's system continues, the 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); both ducts ''drain'' into the circulatory system at the right and left [[subclavian vein]]s. The system collaborates with white blood cells in lymph nodes to protect the body from being infected by cancer cells, fungi, viruses or bacteria. This is known as a secondary circulatory system.

==Function of the fatty acid transport system==

[[Lymph vessel]]s called [[lacteals]] are present in the lining of the [[gastrointestinal tract]], predominantly in the small intestine. While 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 (lipids) 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]]. As the blood circulates, fluid leaks out into the body tissues.  This fluid is important because it carries food to the cells and waste back to the bloodstream.  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, transporting interstitial fluid back to blood.

==Pathology==
In [[elephantiasis]], infection of the lymphatic vessels cause a thickening of the skin and enlargement of underlying tissues, especially in the legs and genitals. It is most commonly caused by a [[parasitic disease]] known as [[lymphatic filariasis]].

[[Lymphedema]] also causes abnormal swelling, especially in the appendages (though the face, neck, and abdomen can also be affected).  It occurs if the lymphatic system is damaged, or underdeveloped in some way.  An estimated 170 million suffer with the disorder.
There are three stages:
<br />'''Stage 1''': Pressing the swollen limb leaves a pit that takes a while to fill back in.  Because there is little fibrosis (hardening) it is often reversible.  Elevation reduces swelling.
<br />'''Stage 2''': Pressure does not leave a pit.  Elevation does not help.  If left untreated, the limb becomes fibrotic.
<br />'''Stage 3''': This stage of lymphedema is often called elephantiasis.  It is generally only in the legs after lymphedema that has gone long untreated.  While treatment can help a little, it is not reversible.

Some common causes of swollen lymph nodes include [[staph]] infections, [[infectious mononucleosis]] and [[neoplasm]], e.g. Hodgkin's and [[non-Hodgkin's lymphoma]], and [[metastasis]] of cancerous cells via the lymphatic system.

==Development of lymphatic tissues==
Lymphatic tissues begin to develop by the end of the fifth week of embryonic life. Lymphatic vessels develop from lymph sacs that arise from developing veins, which are derived from [[mesoderm]].

The first lymph sacs to appear are the paired jugular lymph sacs at the junction of the internal jugular and subclavian veins. From the jugular lymph sacs, lymphatic capillary plexuses spread to the thorax, upper limbs, neck and head. Some of the plexuses enlarge and form lymphatic vessels in their respective regions. Each jugular lymph sac retains at least one connection with its jugular vein, the left one developing into the superior portion of the thoracic duct.

The next lymph sac to appear is the unpaired retroperitoneal lymph sac at the root of the mesentery of the intestine. It develops from the primitive vena cava and mesonephric veins. Capillary plexuses and lymphatic vessels spread form the retroperitoneal lymph sac to the abdominal viscera and diaphragm. The sac establishes connections with the cisterna chyli but loses its connections with neighboring veins.

The last of the lymph sacs, the paired posterior lymph sacs, develop from the iliac veins. The posterior lymph sacs produce capillary plexuses and lymphatic vessels of the abdominal wall, pelvic region, and lower limbs. The posterior lymph sacs join the [[cisterna chyli]] and lose their connections with adjacent veins.

With the exception of the anterior part of the sac from which the cisterna chyli develops, all lymph sacs become invaded by mesenchymal cells and are converted into groups of [[lymph nodes]].

The [[spleen]] develops from mesenchymal cells between layers of the dorsal mesentery of the stomach. The [[thymus]] arises as an outgrowth of the third pharyngeal pouch.

==See also==
* [[Lymphedema]]
* [[Lymphoma]]
* [[American Society of Lymphology]]
* [[Manual lymphatic drainage]]

==References==
{{reflist}}

==External links ==	 
{{commonscat|Lymphatic system}}
*[http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookIMMUN.html Lymphatic System]
*[http://www.innerbody.com/image/lympov.html Lymphatic System Overview] (innerbody.com)


{{Immune system}}
{{organ_systems}}
{{lymphatic_system}}
{{Lymphatics of head and neck}}
{{Lymphatics of upper limbs}}
{{Lymphatics of torso}}
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[[Category:Lymphatic system|*]]

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[[es:Sistema linfático]]
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[[ja:リンパ系]]
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[[yi:לימפעטיק סיסטעם]]
[[zh:淋巴系統]]


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