Reticuloendothelial system - Human Anatomy and Physiology B. Pharma 1st Semester

Reticuloendothelial system


At the end of this lecture, student will be able to

• Explain Reticuloendothelial system

• Name different tissue macrophages

• List functions of RES


• Reticuloendothelial system (RES)

 • Classification of RES cells

• Functions of RES

Reticuloendothelial system and tissue macrophages

• Also known as:

– Monocyte-Macrophage system

– Mononuclear Phagocytic System

– Lymphoreticular system.

• Collection of cells united by the common property of phagocytosis.

• It is a generalized phagocytic system located in all tissues.

• Especially in those tissues where large quantities of particles, toxins, and other unwanted substances must be destroyed

• Ex: spleen, liver, lymph nodes, bone marrow, lungs.

Reticuloendothelial system

• System of cells which have highly phagocytic properties.

• RES consists of:

– Monocytes

– Mobile (wandering) tissue macrophages

– Fixed tissue macrophase or fixed histiocytes


• Largest leucocytes.

• Immature cells present in blood, with little ability to fight infectious agent.

• After 72 hours they enter the tissues to become ‘tissue macrophages’.

• In the tissue they swell to become large in size and cytoplasm is filled with lysosomes.

Functions of monocytes

1. Enter tissue and form tissue macrophages – act as scavengers.

2. Phagocyte several bacteria (up to 100)

3. Engulf large particulate matter, dead tissue cells and senile cells.

4. Along with macrophage involved in phagocytosis & destruction of necrotic material.

5. Co-operate with B & T lymphocyte in both Humoral & Cellular immunity.


• Monocytes leaving the blood become activated and differentiate into macrophages.

• Those that have recently left the blood are sometimes referred to as wandering macrophages.

• Monocyte changes during maturation:

– A. Increase in cell size

– B. Number and complexity of intracellular organelles increase, i.e., Golgi, mitochondria, lysosomes

– C. Increase in intracellular digestive enzymes

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 enter the circulation.

Fixed tissue macrophages

(Known by different name in different sites)


Kupffer cells


Alveolar macrophages


Langerhans cells

Connective tissue






Spleen/Bone marrow/Lymph nodes

Reticular or Dendritic cells


1.   Engulf inorganic particulate matter (carbon & dust particles).

2. When confronted with large insoluble particle, plenty of macrophage fuse together to become ‘Multinucleated Giant Cell’

3. Organic foreign matter such as thorn, fish bone, catgut are destroyed by enzyme action & lysis.

4. Engulf micro-organism, senile WBC, RBC, tissue debris & some parasites.

5. Help ‘T’ & ‘B’ lymphocyte in the acquired immunity by presenting antigens.

Function of Reticuloendothelial system

• Reticuloendothelial system plays an important role in the defence mechanism of the body

• Phagocytic Function: Macrophages are the large phagocytic cells

• When any foreign body invades, macrophages ingest them and liberate the antigenic products of the organism. The antigens activate the helper T lymphocytes and B lymphocytes

• Lysosomes of macrophages contain proteolytic enzymes and lipases, which digest the bacteria and other foreign bodies

• Secretion of Bactericidal Agents: Tissue macrophages secrete 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.

i.     Superoxide (O2–)

ii.    Hydrogen peroxide (H2O2)

iii.   Hydroxyl ions (OH–).

Even the bacteria which cannot be digested by lysosomal enzymes are degraded by these oxidants

• Secretion of Interleukins

• Tissue macrophages secrete

• 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.

• Secretion of Tumor Necrosis Factors (TNF)

 i. TNF-α: Causes necrosis of tumor and activates the immune responses in the body

ii.    TNF-β: Stimulates immune system and vascular response, in addition to causing necrosis of tumor

• Secretion of Transforming Growth Factor: plays an important role in preventing rejection of transplanted tissues or organs by immunosuppression

• Secretion of Colony-stimulation Factor Colony-stimulation factor (CSF)

• Secretion of Platelet-derived Growth Factor Tissue (PDGF) which accelerates repair of damaged blood vessel and wound healing

• Removal of Carbon Particles and Silicon

• Destruction of senile RBCs and release hemoglobin

• Destruction of Hemoglobin


– RES is an innate defense mechanism of the body and is located in all the tissues of the body

– RES works mainly through macrophage

– Macrophage act by Phagocytosis

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