reticuloendothelial cell

Human Physiology and Health Education-I

Unit: Unit-III

Topic: Macrophages

Class: Class-12

Reticuloendothelial System (RES)

  • The reticuloendothelial system, also known as the macrophage system, consists of primitive phagocytic cells vital for the body's defense mechanism.

Macrophage

  • A macrophage is a large cell derived from monocytes.

  • It exhibits the property of phagocytosis, defined as a large phagocytic cell.

Classification of Reticuloendothelial Cells

  • Reticuloendothelial cells can be classified into two types:

    1. Fixed Reticuloendothelial Cells (Tissue Macrophages)

      • Locations:

        • Connective tissue

        • Endothelium of blood sinusoids

        • Reticulum of spleen, lymph nodes, and bone marrow

        • Meningocytes of meninges

        • Alveoli of lungs

        • Subcutaneous tissues

    2. Wandering Reticuloendothelial Cells

      • These cells are present in blood and have the ability to migrate.

Functions of the Reticuloendothelial System (Macrophages)

1. Phagocytic Function

  • Macrophages, as large phagocytic cells, play a crucial role in defense by ingesting foreign bodies through phagocytosis.

  • They release antigenic products that activate helper T-lymphocytes and B-lymphocytes.

2. Secretion of Bactericidal Agents

  • Some macrophages secrete substances that destroy bacteria:

    • Superoxide

    • Hydrogen Peroxide

    • Hydroxyl Ions

3. Secretion of Interleukins

  • Macrophages secrete interleukins that facilitate the maturation of lymphocytes:

    • Interleukin-1: Accelerates B and T-lymphocyte production.

    • Interleukin-6: Promotes the growth of B-lymphocytes.

    • Interleukin-12: Accelerates T-lymphocyte production.

4. Secretion of Tumor Necrosis Factor (TNF)

  • Two types of TNF are secreted by tissue macrophages:

    • TNF-α: Induces tumor necrosis and activates immune responses.

    • TNF-β: Stimulates immune system and vascular response, causing tumor necrosis.

5. Secretion of Transforming Growth Factor

  • Tissue macrophages secrete transforming growth factor which plays a pivotal role in preventing the rejection of transplanted tissues/organs through immune suppression.

6. Secretion of Colony Stimulating Factor

  • M-CSF (Macrophage Colony-Stimulating Factor) is secreted by tissue macrophages and promotes the growth of granulocytes, monocytes, and macrophages.

7. Secretion of Platelet-Derived Growth Factor (PDGF)

  • Tissue macrophages secrete PDGF that enhances the repair of damaged blood vessels and aids wound healing.

8. Removal of Inhaled Substances

  • Tissue macrophages ingest carbon particles and silicon entering the body.

9. Destruction of Senile Red Blood Cells

  • Macrophages in the spleen destroy senile RBCs, releasing hemoglobin in the process.

10. Hemopoietic Function

  • Tissue macrophages also play a significant role in blood cell production.