-
- talking about in the lymph node
- medullary cord: loose CT, highly cellular (has reticular fibers, plasma cells, lymphocytes, fibroblasts, neutrophils)
medullary sinus: venous channel running between cords, discontinuous endothelium, traversed by reticular fibers
-
What's the difference between lymph node and splenic cords & sinuses?
- splenic nodes and sinuses are similar to lymph node medullary cords & sinuses but:
- 1) have blood cells in BOTH cords & sinuses
- 2) do NOT have reticular fibers transversing the sinuses
 - silver stain: recticular fiber gaps represent the spleen sinuses
-
What is the order in which lymphocytes traverse a lymph node?
- lymph is dumped from the afferent lymphatic --> subcapsular sinus --> trabeculum --> medullary sinus then cord then sinus --> efferent lymphatic
- * metastatic cells can also use this pathway to move throughout the body (achilles heel of the lymph system)
-
- the white invagination = trabeculum
- can see the lymph node's:
- nodules (follicles) diffuse T-cells, and plasla cells in the medulla CT
-
What are the three mechanisms that assure interaction between lymphocytes & pathogens?
- 1) sinuses are lined by a discontinuous endothelium
- 2) reticular fibers traverse ALL sinuses (lymph node not spleen)
 - 3) afferent lymphatics outnumber efferent; bottleneck results (take a while for lymph to leave, makes it more likely they'll come in contact with a pathogen)
-
- High endothelial venules (HEV)
- specialized post-capillary venous swellings characterized by plump endothelial cells (as opposed to the usual thinner endothelial cells found in regular venules)
- lymphocytes circulating in the blood can directly enter a lymph node by crossing through the HEV)
- found in all secondary lymphoid organs (EXCEPT spleen where blood exits through open arterioles and enters the red pulp) including MALTs, tonsils, pharyngeal adenoids, Peyer's patches in the small intestine, & appendix
-
What distinguishes Hodgkin's lymphoma from non-Hodgkin's lymphoma?
- Reed-Sternberg cells - present only in present in hodgkin's lymphoma
 - characteristic "owl-eye" appearance
- bilobed nucleus w/ really prominent nucleolus
-
lymph nodes & HIV infection
- virus targets helper T cells and either kills them directly or indirectly as a result of cytotoxic T-cell activity that recognizes infected cells as foreign
- with no helper T-cells, production of activated B lymphocytes drops
- marked changes evident in germinal centers: do not contain proliferating B- cells & thus produce no “plasmablasts"
- contain only dendritic cells and macrophages
-
lymphomas
excess proliferation of lymphocytes can lead to lymphomas, solid tumors of the lymphatic system
-
Spleen Functions
- 1) Immune response, B & T cells
- 2) Destroys damaged, senescent blood cells
- 3) Sequesters monocytes
- 4) Hematopoiesis (fetal development)
- 5) Storage of blood/platelets
- 6) Recycling of iron
-
How can you tell the difference between a trabecular artery and a trabecular vein?
- trabecular artery
trabecular vein has LESS smooth muscle
-
White pulp
- the lymphoid component of the spleen organized to maximize interactions between blood borne antigens and cells of the immune system
- consists of both nodular and diffuse lymphoid tissue organized around arteries (PALS)
- arteries surrounded by PALS are known as central arteries
- from these, smaller branches extend to the periphery of the white pulp and terminate in marginal sinuses
-
Red Pulp
- vascular component of the spleen is organized to promote red cell/macrophage interactions
- functions to filter the blood of antigens, microorganisms, and defective or worn-out red blood cells
- terminal, sheathed capillaries empty into the meshwork of red pulp cords (CT) where blood cells must traverse the sinusoidal wall in order to gain entry into the sinuses
-
spleen has an open circulatory system
traversing the narrow “filtration slits” between adjacent endothelial cells (stave cells) requires flexibility, a characteristic that diminishes with red cell agered cells that cannot traverse the filtration slits will be cleared by macrophages
-
What makes up the red pulp cords?
- loose connective tissue/reticular fibers
- cellular elements: red blood cells, platelets, macrophages, plasma cells lymphocytes
-
periarterial lymphatic sheath (PALS) surround central arteries and containing a nodule with a germinal center
-
the Marginal Zone is the interface between the NON-lymphoid red pulp and the LYMPHOID white-pulp of the spleen
|
|