Flashcards in TBL14 - Lymph Nodes Deck (15):
How many lymph nodes are scattered throughout the body? What occupy the lymph nodes? What function does this serve?
1) 500-600 lymph nodes are scattered throughout the body
2) Billions of immunocompetent lymphocytes occupy the lymph nodes; thus, pathogenic antigens residing in the incoming lymph are readily exposed to the lymphocytes
What do B cells do once they react with an antigen? What do B cells form in the lymph nodes?
1) B cells that selectively react with the antigens undergo replication
2) Like activated B cells of MALT, the B cell progeny form lymphoid nodules in the lymph nodes
What are lymph nodes surrounded by and organized into? What accounts for dark staining of the cortex?
1) Lymph nodes are surrounded by dense connective tissue capsules and organized into a darkly stained outer cortex and paler stained central medulla
2) The lymphoid nodules in the cortex account for its dark staining
Trabeculae that extend from the capsule are spanned by what?
Trabeculae that extend from the capsule are spanned by a three-dimensional reticular fiber meshwork that provides a suspension system for the resident lymphocytes
What forms the reticular fibers?
Type III collagen forms the thin reticular fibers, which unlike the cable-like type I collagen fibers of the capsule, are interwoven into the fine fibrous meshwork
What are venules lined with and where do they reside? What does the endothelia of venules do?
1) Venules, which are lined with simple cuboidal endothelium (aka high endothelial venules or HEV), reside along the boundary of the medulla and the cortex
2) HEV endothelia selectively bind to circulating B cells and T cells and thereby enable the lymphocytes to migrate from the bloodstream into the reticular fiber meshwork of the cortex
Where do arteries enter a lymph node and what do they do? What do the HEV empty into?
1) Arteries enter the hilum and supply the medullary and cortical capillaries, which drain into the HEV
2) HEV empty into veins that exit the lymph node at the hilum
What other vessels enter the lymph node?
Multiple afferent lymphatic vessels pierce the capsule and deliver lymph into the lymph node
Where do lymphatic vessels deliver lymph to? What two sinuses are continuous with one another? What do the sinuses do?
1) Afferent lymphatic vessels deliver lymph directly into the subcapsular sinus
2) The sinus is continuous with the trabecular sinus
3) The sinuses, which are lined by discontinuous endothelium, contribute to the filtration of lymph as it percolates through the lymph node
What are macrophages closely associated with?
Macrophages closely associate with the sinuses; thus, pathologic antigens are readily filtered from the percolating lymph by the macrophages and surrounding B cells
What do the sinuses weave among?
The trabecular sinuses are continuous with the medullary sinuses that weave among the medullary cords, which are linear aggregates of antigen-activated lymphocytes and plasma cells that migrated from the cortical lymphoid nodules into the medulla
What accounts for pale staining of the medulla? What travels from the medullary cords?
1) Extensive branching of the medullary sinuses accounts for pale staining of the medulla
2) From the medullary cords, activated lymphocytes and plasma cell-derived antibodies easily traverse the porous medullary sinuses to enter the percolating lymph
What does coalescence of the medullary sinuses form?
Coalescence of the medullary sinuses forms a single efferent lymphatic vessel that at the hilum, transports filtered lymph with added activated lymphocytes and selective antibodies out of the lymph node
What conditions can cause lymphadenopathy?
1) Abnormal enlargement of lymph nodes, or lymphadenopathy, may be due to increased numbers of lymphocytes and macrophages in the node during antigenic stimulation in a bacterial or viral infection
2) It may also be caused by metastasis, whereby neoplastic cells spread from a local site of development to distant locations. Such cells are often carried by lymphatics to the nearest lymph node