GENERAL KEY POINTS

The lymphatic system has four major functions:

• 1.
  

  Produce, store and re-circulate lymphocytes , cells mainly responsible for immune response in the body.

  
  
• 2.
  

  Store macrophages (phagocytes).

  
  
• 3.
  

  Drain surplus tissue fluid to the bloodstream.

  
  
• 4.
  

  Transport absorbed fat from the intestine to the bloodstream.

The combined fluid product is known as lymph .

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  Lymph is drained from areas of tissue via very fine threadlike lymphatic vessels ( lymphatics ), that are thin walled, similar to veins , and have valves to ensure one-way flow .

  
  
• •
  

  Lymph flow is chiefly maintained by external pressure on the delicate-walled lymphatic vessels by surrounding tissue structures.

  
  
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  Lymphatics connect to main trunks and are interrupted en route by lymphoid organs and nodes , which act as filters.

  
  
• •
  

  Afferent lymphatic vessels carry unfiltered lymph into a node .

  
  
• •
  

  Efferent lymphatic vessels carry filtered lymph out of a node .

  
  
• •
  

  Several main lymphatic trunks converge towards their venous junction (cervical lymphovenous portals), returning lymph to the venous bloodstream.

There are normally three trunks on the right side of the body and four on the left .

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  The main lymphoid organs of the body are the tonsils , spleen , thymus and lymph nodes , of which some 400–450 are present in the normal adult.

  
  
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  Lymph nodes are sited regionally and may be found as singleton , pairs or in distinct multiple cluster groups ( Fig. 24 ).

  
  

  
  

  
  

  

  
  

  
  

  A cluster (group) of adult upper limb left axillary (lateral) lymph nodes with associated vessels. They are shown actual size as presented at dissection and are typical of normal lymph node appearance in the human body.

  
  
  
  
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  Nodes are usually small , ovoid or kidney (reniform) in shape and vary between 0.1 and 2.5 cm in length.

  
  
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  Some nodes , but not all , may be palpable in their normal state , but particularly so when diseased.