<P> Like the thymus, the spleen possesses only efferent lymphatic vessels . The spleen is part of the lymphatic system . Both the short gastric arteries and the splenic artery supply it with blood . </P> <P> The germinal centers are supplied by arterioles called penicilliary radicles . </P> <P> The spleen is unique in respect to its development within the gut . While most of the gut organs are endodermally derived (with the exception of the neural - crest derived adrenal gland), the spleen is derived from mesenchymal tissue . Specifically, the spleen forms within, and from, the dorsal mesentery . However, it still shares the same blood supply--the celiac trunk--as the foregut organs . </P> <Table> <Tr> <Td> Area </Td> <Td> Function </Td> <Td> Composition </Td> </Tr> <Tr> <Td> red pulp </Td> <Td> Mechanical filtration of red blood cells . In mice: Reserve of monocytes </Td> <Td> <Ul> <Li> "sinuses" (or "sinusoids"), which are filled with blood </Li> <Li> "splenic cords" of reticular fibers </Li> <Li> "marginal zone" bordering on white pulp </Li> </Ul> </Td> </Tr> <Tr> <Td> white pulp </Td> <Td> Active immune response through humoral and cell - mediated pathways . </Td> <Td> Composed of nodules, called Malpighian corpuscles . These are composed of: <Ul> <Li> "lymphoid follicles" (or "follicles"), rich in B - lymphocytes </Li> <Li> "periarteriolar lymphoid sheaths" (PALS), rich in T - lymphocytes </Li> </Ul> </Td> </Tr> </Table>

Old and defective erythrocytes are removed from circulation in the of the spleen