SPLEEN:
The spleen plays a major role in mounting immune response to antigens in the blood stream.It is a large,ovoid secondary organ sitauted high in the left abdominal cavity.While lymph nodes are specialized for trapping antigen from local tissues,the spleen specializes in filtering blood and trapping blood-borne antigens;thus ,it can reepond to systemic infections.Unlike the lymph nodes,the spleen is not supplied by lymphatic vessels.Instead,blood-borne antigens and lymphocytes are carried into spleen through the splenic artery.
The spleen is surrounded by a capsule that extends a number of projections(trabaculae)into the interior to form a compartmentalized structure.The compartments are of two types,the red pulp and white pulp,which are separated by a diffuse marginal zone.The splenic red pulp consists of a network of sinusoids populated by macrophages and numerous red blood cells(erythrocytes)and few lymphocytes;it is the site where old and defective red blood cells are destroyed and removed.Many of the macrophages within the red pulp contain engulfed red blood cells or iron pigments from degraded hemoglobin.The splenic white pulp surrounds the branches of the splenic artery,forming a periarteriolar lymphoid sheath(PALS)populated mainly by T lymphocytes.Primary lymphoid follicles are attached to thePALS.These follicles are rich in B cells and some of them contain germinal centers.The marginal zone,located peripheral to the PALS,is populated by lymphocytes and macrophages.
The spleen plays a major role in mounting immune response to antigens in the blood stream.It is a large,ovoid secondary organ sitauted high in the left abdominal cavity.While lymph nodes are specialized for trapping antigen from local tissues,the spleen specializes in filtering blood and trapping blood-borne antigens;thus ,it can reepond to systemic infections.Unlike the lymph nodes,the spleen is not supplied by lymphatic vessels.Instead,blood-borne antigens and lymphocytes are carried into spleen through the splenic artery.
The spleen is surrounded by a capsule that extends a number of projections(trabaculae)into the interior to form a compartmentalized structure.The compartments are of two types,the red pulp and white pulp,which are separated by a diffuse marginal zone.The splenic red pulp consists of a network of sinusoids populated by macrophages and numerous red blood cells(erythrocytes)and few lymphocytes;it is the site where old and defective red blood cells are destroyed and removed.Many of the macrophages within the red pulp contain engulfed red blood cells or iron pigments from degraded hemoglobin.The splenic white pulp surrounds the branches of the splenic artery,forming a periarteriolar lymphoid sheath(PALS)populated mainly by T lymphocytes.Primary lymphoid follicles are attached to thePALS.These follicles are rich in B cells and some of them contain germinal centers.The marginal zone,located peripheral to the PALS,is populated by lymphocytes and macrophages.
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