1. RK Goit, Lecturer
Department of Physiology
Nepalgunj Medical College, Nepal

2. 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• Therefore, the term reticuloendothelial system is obsolete.

4. 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

5. 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

6. 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

7. 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

8. Tissue macrophages in the spleen & bone
• if an invading organism succeeds in entering the general
circulation, there are other lines of defense

9. 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

10. Tissue macrophages in the skin & subcutaneous tissues
(Histiocytes)
• 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

11. 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

12. 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

13. 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’

14. 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

15. • 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

17. 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

18. Thank You