What are the functions of the Lymphatic System?
- to protect the body against pathogenic organisms and their products
- to help in the removal and disposal of cells undergoing natural or induced degenerations
What is the function of the primary lymphatic organs?
List the organs
generate lymphocytes from progenitor cells
- bone marrow
- cloacal bursa/bursa of fabricius
- thymus
What is the function of the secondary lymphatic organs?
List the organs
sites of lymphocyte activation/differentiation in context of immune response
- lymph nodes
- spleen
- mucosal associated lymphoid tissue
Describe the Bone Marrow
- source of pluripotent cells
- B cells mature
- contains a background of stromal cells that release factors aiding cell differentiation, and macrophages
What is the Cloacal Bursa?
- Bursa of Fabricius
- bird equivalent of bone marrow
- contain nodules full of lymphoid cells with B cell rich cortex
- background of stromal cells and macrophages
Describe the Thymic Cortex
- stains darker due to increased number of lymphocytes
- area of positive selection
What are the functions of the stromal cells?
- clear up debris
- release factors that help environment for differentiation
Describe the Thymic Medulla
- contains more prominent reticular cells
- area of negative selection
- tingible body macrophages eliminate dead T cells
- presence of Hassall’s corpuscles
What are Hassall’s Corpuscles?
large central calcified or degenerated cells surrounded by concentric circles of keratinized cells
What is the function of lymph nodes?
- to filter antigens from lymph before returning it to bloodstream
What is the Hilus?
a slight indentation in the lymph node where arteries enter, and veins and efferent vessels leave
What is the pathway of the lymph through the lymph node?
afferent vessel subcapsular sinus cortical sinus medullary sinus efferent vessel
What is the function of the spleen?
- filters blood
- removes antigens from blood
- mounts immune response
- stores RBCs and platelets (not cats)
- iron recycling
What does the red pulp in the spleen contain?
- sinusoids
- macrophages and blood cells
What does the white pulp in the spleen contain?
- B cells in follicles
- T cells around central arterioles
- periarteriolar lymphoid sheaths
Explain the blood flow through the spleen
central artery > branches to penicillary arteries > end in sheathed capillaries > parenchymal space > sinuses > splenic vein > hepatic portal vein
List the Mucosal Associated Lymphoid Tissues
- gut-associated lymphoid tissue (GALT)
- bronchial-associated lymphoid tissue (BALT)
- tonsil
- ocular
- urogenital
- mammary
Describe Peyer’s Patches
- aggregation of lymphatic nodules in submucosa of small intestine
- B cells migrate here, some level of maturation
- may involute with age
- have lacteals or lymphatic vessels
What is the function of Peyer’s Patches?
to take nutrients in the form of chylomicrons to various parts of the body
What are lacteals?
blind-ended lymphatic capillaries within intestinal villi of the chyle to lymphatic vessels
What are M cells and what is their function?
- specialized epithelial cells that sit above Peyer’s patches
- pinocytose GI contents and secrete contents on lymphocytes and macrophages of the patches
What are some features of the tonsils?
- no afferent lymphatic vessels
- presence of crypts
