Lymphatic

• Lymph


  Interstitial fluid once it has entered lymphatic vessels; contains many proteins, microbes, cancer cells
• Lymphatic system


  • Consists of two semi-independent parts: a meandering network of lymphatic vessels, and lymphoid tissues and organs scattered throughout the body
  • Functions: Returns interstitial fluid and leaked plasma proteins back to the blood, absorbs fat in small intestine, filters/destroys foreign antigens
• Lymphatic capillaries


  Similar to blood capillaries, yet more permeable with endothelial minivalves that remain open and withstand pressure; Allow interstitial fluid to enter, but not to escape from lymph capillaries; Keep lymph flowing in a one-way direction; During inflammation, can absorb cell debris, pathogens, and cancer cells

  
• Lymphatic collecting vessels


  Have thinner walls, with more internal valves than veins and more anastomoses; Travel with arteries/veins; Nutrients are supplied from branching vasa vasorum

  
• Lymphatic trunks


  Formed by the union of the largest collecting vessels; Major trunks include: paired lumbar, intercostal, bronchiomediastinal, subclavian, and jugular trunks and a single intestinal trunk; Lymph is ultimately drained into one of two large ducts: Right lymphatic duct and Thoracic duct

  
• Diffuse lymphatic tissue


  Scattered reticular tissue elements in every body organ with many macrophages and lymphocytes

  
• Lymphatic nodules


  Solid, spherical bodies consisting of tightly packed reticular elements and cells; Have a germinal center composed of maturing B cells; Examples: Peyer's Patches, Tonsils, and Appendix
• Peyer's Patches


  Isolated clusters of lymphoid tissue, similar to tonsils, found in small intestine (esp. ileum); Destroy bacteria and preventing them from breaching the intestinal wall

  
• Tonsils


  Located in oro/nasopharynx; Filters air: removes foreign materials; Contains Tonsillar Crypts to trap microbes; Types: Pharyngeal (adenoids), Palatine, and Lingual

  
• Red bone marrow


  A primary lymphoid organ (site of B and T lymphocyte production; site of B lymphocyte maturation); Formed in Children: medullary cavity of long bones; Formed in Adults: axial skeleton and proximal heads of humerus and femur; Contains sinusoids with macrophages that destroy malformed blood cells
• Thymus


  A primary lymphoid organ (site of T lymphocyte maturation); A bilobed organ that secrets hormones (thymosin) that cause maturation of T lymphocyte cells; The size of the thymus varies with age, stops growing during adolescence and then gradually atrophies; Important for development of entire immune system
• Lymph nodes


  The principal lymphoid organs of the body; Aggregations of these nodes occur near the body surface in thoracic, abdominal, intestinal/mesenteric, popliteal, inguinal, axillary, and cervical regions of the body; Swell with infection or cancer; The cortex contains follicles with germinal centers, heavy with maturing B cells; The deep cortex houses T cells in transit

  
• Spleen


  Largest lymphoid organ; Functions: Site of B lymphocyte production, Cleanses the blood, Stores products of RBC breakdown for later reuse, Spleen macrophages salvage and store iron for later use by bone marrow, Site of fetal erythrocyte production (normally ceases after birth), Stores blood platelets
• The spleen can often repair itself, resulting in dramatically decreasing emergency surgeries
• White pulp of the spleen

  Area containing mostly lymphocytes suspended on reticular fibers and involved in immune functions (lymphocyte maturation)
• Red pulp of the spleen

  Remaining splenic tissue concerned with disposing of worn-out RBCs and bloodborne pathogens