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RK Goit, Lecturer
Department of Physiology
Nepalgunj Medical College, Nepal
Reticuloendothelial system
• phagocytosis – ingestion of microbes or foreign cells or solid materials by a phagocyte
• phagocytes are neutrophils, monocytes & macrophages
• monocytes transform themselves into macrophages in tissue
• these macrophages are mononuclear cells, & this system of phagocytes is called as mononuclear phagocyte system (MPS)
• this system of cells was known as reticuloendothelial system– neither they are reticular in appearance
– nor they have endothelial origin
• Therefore, the term reticuloendothelial system is obsolete.
Macrophages (Kupffer cells) in the liver sinusoids
bacteria from ingested food pass through GIT into the portal blood
↓
it passes through the sinusoids of the liver
↓
these sinusoids are lined with Kupffer cells
↓
these cells form an effective particulate filtration system
Alveolar macrophages in the lungs
• organisms enter the body through the lungs
• macrophages can phagocytize particles
1. if the particles are digestible, the macrophages can digest them & release the digestive products into the lymph
2. if the particle is not digestible, the macrophages often form a “giant cell” capsule around the particle→ slowly dissolve
Microglia of brain
• microglia cells in brain & spinal cord appear to be inactive
• in inflammatory disease of the CNS, they become the immune effector cells
• they proliferate & become antigen presenting cells
Tissue macrophages in the lymph nodes
• if the particles are not destroyed locally in the tissues, they enter the lymph & flow to the lymph nodes
• foreign particles are then trapped in these nodes in a meshwork of sinuses lined by tissue macrophages
Tissue macrophages in the spleen & bone
• if an invading organism succeeds in entering the general circulation, there are other lines of defense
Mesangial cells in kidney
• are an unusual example of phagocytic cells derived from smooth muscle & not monocytes
• aid neutrophils in removing other mesangial cells undergoing apoptosis & also other debris in glomerulus
• when infection begins in a subcutaneous tissue & local inflammation ensues, local tissue macrophages can divide in situ & form still more macrophages
• then they perform the usual functions of attacking & destroying the infectious agents
Tissue macrophages in the skin & subcutaneous tissues (Histiocytes)
1. Phagocytic function– when any foreign body invades, macrophages ingest them by
phagocytosis & liberate the antigenic products of the organism
– antigens activate the helper T lymphocytes & B lymphocytes
2. Secretion of bactericidal agents– secrete many bactericidal agents which kill the bacteria
I. Superoxide (O-2)
II. Hydrogen peroxide (H2O2)
III. Hydroxyl ions (-OH-)
3. Secretion of interleukins– IL-1: accelerate maturation & proliferation of specific B
lymphocytes & T lymphocytes
– IL-6: cause growth of B lymphocytes
– IL-12: influence the T-helper cells
4. Secretion of tumor necrosis factors
– TNF-α: causes necrosis of tumor & activates the immune responses in the body
– TNF-β: stimulates immune system
5. Secretion of platelet derived growth factor
– accelerates repair of damaged blood vessel & wound healing
6. Secretion of colony stimulation factor
– M-CSF accelerates growth of granulocytes, monocytes & macrophages
7. Removal of carbon particles & silicon
– ingest the substances like carbon dust particles & silicon which enter the body
8. Destruction of RBC
– remove aged RBC
9. Giant cell
– 20 or more macrophages can fuse to form a multinucleate ‘giant cell’ that engulfs a bacillus
10. Foam cells
– macrophages store excess lipids & mucoprotein & become swollen to form ‘foam cells’
Functions of spleen
• Formation of blood cells
– play in important role in the hemopoietic function in embryo
– during the hepatic stage, spleen produces the blood cells along with liver
• Destruction of blood cells
– the older RBCs, lymphocytes & thrombocytes are destroyed in the spleen
• Reservoir function
– a large number of RBCs are stored in spleen
– RBCs are released form spleen into circulation during the emergency conditions like hypoxia & hemorrhage
• Role in defense of body
– spleen filters the blood by removing the microorganism
– macrophages in splenic pulp phagocytose the microorganism & other foreign bodies
– spleen contains about 25% of T lymphocytes & 15% of B lymphocytes & form the site of antibody production
Functions of lymph nodes
Lymph nodes serve as filters which filter bacteria & toxic substances form the lymph.
• when lymph passes through the lymph nodes, it is filtered i.e. the water & electrolytes are removed
– but the proteins & lipids are retained in the lymph
• bacteria & other toxic substances are destroyed by macrophages of lymph nodes
Thank You
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