Lymphatics
Tubular vessels transport back lymph to the blood ultimately replacing the volume lost from the blood during the formation of the interstitial fluid. These channels are the lymphatic channels or simply called lymphatics.
Function of the fatty acid transport system
Lymph vessels 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. (There are exceptions, for example medium-chain triglycerides (MCTs) are fatty acid esters of glycerol that passively diffuse from the GI tract to the portal system.) 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.
Diseases of the lymphatic system
Lymphedema is the swelling caused by the accumulation of lymph fluid,[7] which may occur if the lymphatic system is damaged or has malformations. It usually affects the limbs, though face, neck and abdomen may also be affected.
Some common causes of swollen lymph nodes include infections, infectious mononucleosis, and cancer, e.g. Hodgkin's and non-Hodgkinlymphoma, and metastasis of cancerous cells via the lymphatic system. 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. Lymphangiosarcoma is a malignant soft tissue tumor, whereas lymphangioma is a benign tumor occurring frequently in association with Turner syndrome. Lymphangioleiomyomatosis is a benign tumor of the smooth muscles of the lymphatics that occurs in the lungs.
Some common causes of swollen lymph nodes include infections, infectious mononucleosis, and cancer, e.g. Hodgkin's and non-Hodgkinlymphoma, and metastasis of cancerous cells via the lymphatic system. 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. Lymphangiosarcoma is a malignant soft tissue tumor, whereas lymphangioma is a benign tumor occurring frequently in association with Turner syndrome. Lymphangioleiomyomatosis is a benign tumor of the smooth muscles of the lymphatics that occurs in the lungs.
Development of lymphatic tissue
Lymphatic tissues begin to develop by the end of the fifth week of embryonic development. 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 from 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.
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 from 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.
Lymphatico-Venous Communications
Present research has found cues about a lymphatico-venous communication. In mammals, lymphatico-venous communications other than those at the base of the neck are not easy to demonstrate, but described in some experiments.[8]
The specialists observed that the pulmonary complications following lymphangiography (a test which utilizes X ray technology, along with the injection of a contrast agent, to view lymphatic circulation and lymph nodes for diagnostic purposes)are more often severe in patients with lymphatic obstruction. In these cases, the contrast medium is thought to reach the vascular system via lymphovenous communications with shunt the material directly into the venous stream, bypassing those lymph nodes distal to the communications,[9] Because less contrast agent is absorbed in lymph nodes, a greater portion of the injected volume passes into the vascular system. Since pulmonary complications are related to the amount of medium reaching the lungs area, the early recognition of lymphovenous communications is a great significance to the lymphangiographer.[9] Another "hint" in proving a lymph-vein communication is offered by a Robert F Dunn experiment. The passage of radioactively tagged tracers, injected at elevated pressure, through the lymph node-venous communications coincides with the increased pressures of injection and subsequent nodal palpation in dogs. The passage of iodinated I 125 serum albumen (ISA) indicates that direct lymph node-venous communications are present, whereas passage of nucleated erythrocytes requires a communication structure the size of a capillary or larger.[10] Moreover, the evidence suggest that in mammals under normal conditions, mostly of the lymph is returned to the blood stream through the lymphatico-venous communications at the base of the neck. When the thoracic duct-venous communication is blocked, however, the resultant raised intralymphatic pressure will usually cause other normal non-functioning communications to open and thereby allow the return of lymph to the blood stream.[
The specialists observed that the pulmonary complications following lymphangiography (a test which utilizes X ray technology, along with the injection of a contrast agent, to view lymphatic circulation and lymph nodes for diagnostic purposes)are more often severe in patients with lymphatic obstruction. In these cases, the contrast medium is thought to reach the vascular system via lymphovenous communications with shunt the material directly into the venous stream, bypassing those lymph nodes distal to the communications,[9] Because less contrast agent is absorbed in lymph nodes, a greater portion of the injected volume passes into the vascular system. Since pulmonary complications are related to the amount of medium reaching the lungs area, the early recognition of lymphovenous communications is a great significance to the lymphangiographer.[9] Another "hint" in proving a lymph-vein communication is offered by a Robert F Dunn experiment. The passage of radioactively tagged tracers, injected at elevated pressure, through the lymph node-venous communications coincides with the increased pressures of injection and subsequent nodal palpation in dogs. The passage of iodinated I 125 serum albumen (ISA) indicates that direct lymph node-venous communications are present, whereas passage of nucleated erythrocytes requires a communication structure the size of a capillary or larger.[10] Moreover, the evidence suggest that in mammals under normal conditions, mostly of the lymph is returned to the blood stream through the lymphatico-venous communications at the base of the neck. When the thoracic duct-venous communication is blocked, however, the resultant raised intralymphatic pressure will usually cause other normal non-functioning communications to open and thereby allow the return of lymph to the blood stream.[