Reticuloendothelial System and Tissue Macrophage.pptx

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1. Reticuloendothelial System and Tissue Macrophage

2. D EFINITION AND DISTRIBUTION RETICULOENDOTHELIAL SYSTEM OR MACROPHAGE SYSTEM Reticuloendothelial system or tissue macrophage system is the system of primitive phagocytic cells, which play an essential role particularly in defense mechanism of the body. The reticuloen - dothelial cells are observed in the following structures: 1. Endothelial lining of vascular and lymph channels. 2. Connective tissue and some organs like spleen, liver, lungs, lymph nodes, bone marrow, etc. Reticular cells in these tissues are responsible regarding formatiom of the tissue macrophage system.

3. MACROPHAGE Macrophage is a large phagocytic cell, derived from monocyte . CLASSIFICATION OF RETICULOENDOTHELIAL CELLS Reticuloendothelial cells are classified into two types: 1. Fixed reticuloendothelial cells or tissue macrophages. 2. Wandering reticuloendothelial cells.   FIXED RETICULOENDOTHELIAL CELLS – TISSUE MACROPHAGES Fixed reticuloendothelial cells are also termed as the tissue macrophages or fixed histiocytes because, these cells are usually l found in the tissues.

4. FUNCTIONS OF RETICULOENDOTHELIAL SYSTEM Tissue macrophages are present in the following areas: 1. Connective Tissue Reticuloendothelial cells in connective tissues and in serous membranes like pleura, omentum and mesentery are known as the fixed macrophages of connective tissue. 2. Endothelium of Blood Sinusoid Endothelium of the blood sinusoid in bone marrow, liver, spleen, lymph nodes, adrenal glands and pituitary glands also consist of fixed cells. Kupffer cells present in liver belong to this category. 3. Reticulum Reticulum of spleen, lymph node and bone marrow c onsists of fixed reticuloendothelial cells. 4. Central Nervous System Meningocytes of meninges and microglia play an important role regarding the formation of the tissue macrophages of brain. 5. Lungs Tissue macrophages are observed in the alveoli of lungs. 6. Subcutaneous Tissue Fixed reticuloendothelial cells are seen in subcutaneous tissue also.

5. WANDERING RETICULOENDOTHELIAL CELLS AND TISSUE MACROPHAGES Wandering reticuloendothelial cells are also termed as free histiocytes. There are two types of wandering reticuloendothelial cells:   1. Free Histiocytes of Blood i. Neutrophils ii. Monocytes, which become macrophages and migrate to the site of injury or infection. 2. Free Histiocytes of Solid Tissue During emergency, the fixed histiocytes from connective tissue and other organs become wandering cells and gain entry into the circulation.

6. FUNCTIONS OF RETICULOENDOTHELIAL SYSTEM Reticuloendothelial system plays an important role in the defense mechanism of the body. Most of the functions of the reticuloendothelial system are performed by the tissue macrophages.   Functions of tissue macrophages: 1. Phagocytic Function Macrophages are the large phagocytic cells, which play an important role regarding defense mechanism with the help of phagocytosis. When any foreign body invades, macrophages ingest them with the help of phagocytosis and liberate the antigenic products of the organism. The antigens activate the helper T lymphocytes and B lymphocytes. Lysosomes of macrophages co nsist of proteolytic enzymes and lipases, which digest the bacteria and other foreign bodies. 2. Secretion of Bactericidal Agents Tissue macrophages produce many bactericidal agents which kill the bacteria. The important bactericidal agents of macrophages are the oxidants. An oxidant is a substance that oxidizes another substance. Oxidants produced by macrophages are: i . Superoxide (O2 – ) ii. Hydrogen peroxide (H2 O2 ) iii. Hydroxyl ions (OH– ). These oxidants exhibit most potent bactericidal effects. So, even the bacteria which cannot be digested by lysosomal enzymes are degraded particulaly by these oxidants.  

7. 3. Secretion of Interleukins Tissue macrophages secrete the following interleukins, which assist in immunity: i. Interleukin-1 (IL-1): Accelerates the maturation and proliferation of specific B lymphocytes and T lymphocytes. ii. Interleukin-6 (IL-6): Causes the growth of B lymphocytes and production of antibodies. iii. Interleukin-12 (IL-12): Influences the T helper cells. 4. Secretion of Tumor Necrosis Factors Two types of tumor necrosis factors (TNF) are secreted by tissue macrophages: i. TNF-α: Causes necrosis of tumor and stimulates the immune responses in the body ii. TNF-β: Activates immune system and vascular response, besides in causing necrosis of tumor.

8. 5. Secretion of Transforming Growth Factor Tissue macrophages secrete transforming growth factor, which plays an important role regarding prevention of rejection of transplanted tissues or organs by immunosuppression. 6. Secretion of Colony-stimulation Factor Colony-stimulation factor (CSF) secreted by macrophages is M-CSF. It enhances the growth of granulocytes, monocytes and macrophages. 7. Secretion of Platelet-derived Growth Factor Tissue macrophages secrete the platelet-derived growth factor (PDGF), which enhances repair of damaged blood vessel and wound healing.   8. Removal of Carbon Particles and Silicon Macrophages ingest the substances like carbon dust particles and silicon, which enter the body. 9. Destruction of Senile RBC Reticuloendothelial cells, particularly those in spleen destroy the senile RBCs and release hemoglobin (Chapter 9). 10. Destruction of Hemoglobin Hemoglobin released from broken senile RBCs is broken down by the reticuloendothelial cells

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