 A number of morphologically and functionally diverse organs and tissue organs and tissue contribute to the development of immune responses .  These organs can be distinguished by function as the primary and secondary lymphoid organs .

1. PRIMARY & SECONDARY
LYMPHOID ORGANS

2. ORGANS OF THE IMMUNE SYSTEM :-
 A number of morphologically and functionally
diverse organs and tissue organs and tissue
contribute to the development of immune
responses .
 These organs can be distinguished by function as
the primary and secondary lymphoid organs .

3. Lymphoid organs -
 Bone marrow
 Thymus
 Spleen
 Lymph node
 Tonsils
 Small intestine & appendix
aggregated lymphoid nodules

4. Lymphoid system:
Lymphoid organs are stationed throughout the body
They are concerned with the growth, development and differeciation of
lymphocytes .
There are structurally and functionally diverse lymphoid organs and tissues
They are interconnected by the blood vessels and lymphatic vessels through which
lymphocytes circulate .
Based upon the functional development of the lymphatic cells the lymphoid
organs are classified into 2 groups

5. 1. Primary lymphoid organs / central - BONE MARROW - All lymphocytes arise and B – cell
maturation ,,,,Thymus – T cell maturation
2 Secondary lymphoid organs / peripheral
MALT - MUCOSA ASSOICATED LYMPHOID
TISSUE
GALT – GULT ASSOICATED LYMPHOID TISSUE
SALT – SKIN ASS0ICATED LYMPHOID TISSUE

6. BONE MARROW :-
Bone marrow is primary lymphoid organs .
It is soft tissue within the cavity of bones
It is the site of generation of all circulating blood cells in the adult , including immature
lymphocytes , and is the site of B cells maturation .
All the cells of immune system are initially derived form the bone marrow through a
process called haematopoiesis .
Immature B cells arise from lymphoid progenitors , proliferate and differentiate within
the bone marrow .
Bone marrow also have stromal cells interact direct with B cells and secrets various
cytokines and help in the maturation of B cells .

7. In birds – B cells development in bursa of fabricus .
 Bone marrow is divisible into 2
I. Vascular region
II. Hematopoietic region
 Vascular region is the circulatory system that supplies nutrient and removes waste
from actively growing blood vessels .
 Red bone marrow is actively involved in haematopoiesis .
 Res bone marrow contains titipoent cells called stem cells . The development blood
cells from stem cells is called Haematopoiesis .
 Haematopoiesis is forms RBC , WBC – GRANULOCYTES , Lymphocytes , monocytes &
platlets

8. THYMUS:-
Thymus is the site of T cell differentiation and maturation .
It is flat bilobed organ , situated above heart in the thorax region is lobe is
encapsulated and it is divided into lobules which are separated by strands
of connective tissue called trabeculae .
Each lobules contains - lymphocytes & each lobule organized into two
compartments
1. Outer cortex
2. Inner medulla

10. The cortex contains mostly immature & proliferating thymocytes ,
Medulla is sparly populated with thymocytes .
Some of which Mature and migrate to the medulla – in medulla they
learn to discriminate between self and non self fetal development and
for a short time after birth .
T cells leave the medulla to enter the peripheral blood circulation ,
through which they are transported to the secondary lymphoid organs .
About 95 % of all T cells die in the thymus .

11. Besides lymphoid cells it is composed of
Epithelial cells
Macrophages
Dendritic cells
Nurse cells
Hassall’s corpuscles
Lymphocytes in the thymus are called thymocytes

12. Function of the thymus:-
Generated and select T cells
T LYMP. Cannot recognised antigen it only recognised these antigen which are bound with M
must have protein which recognised MHC .
TH- CD 4- MHC 2nd
+ SELECTION
TC – CD 8th MHC
Thus about 95 % of all T cells die in the thymus .
Change in the thymus with age --

13. Secondary lymphoid organ :-

14.  Red pulp is a site where defective RBC is destroyed

15.  Primary lymphoid follicleS are attached TO THE PALS .
 Marginal zones- located at primary of PALS. They are with lymphocyte and
macrophages .
 Antigen lymphocyte enter into the spleen antigen trapped by D.C ( Dendritic cell)
which carry antigen into PALS .
 lymphocytes also enters into pals so activation of B and T lymphocytes with the help
of dendritic cells .
 Means dendritic cells present antigen In MHC 2ND to TH cells activates B cells.
 B & T cells migrates to primary lymphoid follicle .
 Primary follicle contain germinal centres .
 Germinal centres have specific cells knows as plasma cells.
 Plasma cells produced antibodies .

16. Lymph Node : -
Bean shaped , encapsulated structures distributed throughout the body along the
course of lymphatic vessel .
They are made up of mostly B-cells , T – cells , macrophages and dendritic cells .

17. (MALT)

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