Overview of the lymphatic system

• Lymph - clear, watery fluid, made from reabsorbed interstitial fluid
• What is the lymphatic system?

  • fluid conducting system
  • transports lymph in lymphatic vessels connected by lymph nodes
  • accessory route for reabsorption of interstitial fluid
• Role of lymph

  • draining excess interstitial fluid
  • transporting dietary lipids
  • carries out immune response
  • return lost plasma proteins into circulation
• Lymph maintains circulating volume and blood pressure. 3L reabsorbed per day.
• Lymphatic vessels transport lipids and lipid soluble vitamins
• Lymphatic tissue initiates highly specific responses directed against particular microbes or abnormal cells.
• Lymph capillaries are located in the spaces between cells and are closed at one end.
• Lacteals are lymphatic capillaries found in the small intestine. They carry dietary lipids into the lymphatic vessels and ultimately into the blood. Lymph here is called chyle.
• Lymphatic capillaries are found everywhere except avascular tissues, CNS, portions of the spleen, bone marrow.
• Anchoring filaments attach lymphatic endothelial cells to surrounding tissues. When pressure in interstitial space rises these pull cells apart allowing more fluid to enter.
• Endothelial cells overlap allowing one way flow of lymph.
• Passage of lymph in body

  • lymphatic capillary
  • lymph vessel
  • lymph node
  • lymphatic trunks
  • lymphatic ducts
• Transport of lymph is reliant on two actions

  • skeletal muscle pump - milking action of skeletal muscle contractions
  • respiratory pump - in inhalation lymph travels from abdomen which is under higher pressure to chest which is under lower pressure
• Lymphatic trunks

  • jugular - head and neck
  • subclavian - upper limbs
  • bronchomediastinal - thoracic wall, lung and heart
  • intestinal - stomach, intestines, liver, pancreas, spleen
  • lumbar - drain lower limbs, wall and viscera of the pelvis, kidneys, adrenal glands, abdominal wall
• Right lymphatic duct drains lymph from

  • right jugular
  • right subclavian
  • right bronchomediastinal
• Thoracic duct drains lymph from

  • both lower limbs
  • lumbar and intestinal trunks
  • left jugular
  • left subclavian
  • left bronchomediastinal
• The venous angle is the site of drainage of the lymphatic ducts. The junction of the internal jugular vein and subclavian vein bilaterally
• Right lymphatic duct and left thoracic duct can be injured in neck dissections to remove cancerous lymph nodes. Heat seal (diathermy) or better still ligate (tie off) if seen during surgery. May need to replace fats and protein if damaged with long term leak/fistula.
• Primary lymphatic organs - sites where stem cells divide and become immunocompetent
• Secondary lymphatic organs - where most immune responses occur (lymph nodes, spleen, lymph nodules)
• Lymph nodes

  • encapsulated bean shaped organs
  • act as a filter
  • scattered throughout the body both superficially and deep
  • foreign substances trapped by reticular fibres
• Immune system is comprised of organs and tissues that produce and mature lymphocytes (primary lymphoid organs) and organs that house lymphocytes (secondary lymphoid organs)
• B cells develop and mature in bone marrow
• T cells develop in bone marrow but mature in thymus
• Once B cells and T cells are mature, they migrate to secondary lymphoid organs
• The spleen is the largest single mass of lymphatic tissue, located in the left hypochondrium
• Functions of the spleen

  • immune mediated response
  • degradation of RBCs
  • haematopoesis in fetal life
  • storage of RBC
• The spleen consists of white pulp and red pulp
• Nasopharyngeal tonsils (adenoid) located behind nose, on roof of posterior wall of pharynx, posterior opening of nasal cavity
• lymphatic tissues

  A) thymus

  B) cisterna chyli

  C) lymph nodes

  D) spleen

  E) peyers patch

  
• How much fluid does the lymphatic system return to the circulating volume each day?

  3 L
• How many lymph trunks are there and what are they called?

  5 - jugular, subclavian, bronchomediastinal, lumbar, intestinal
• Name the 2 primary lymphatic organs?

  Thymus and bone marrow
• What is the difference between primary and secondary lymphatic organs?

  Primary is a site of stem cell division and lymphocyte maturation. Secondary is a site of immune response
• What are the two lymphatic ducts?

  Right lymphatic duct and left thoracic duct