The document describes the primary and secondary lymphoid organs of the immune system, detailing their structure and function. Primary lymphoid organs, including the bone marrow and thymus, are essential for the development and maturation of lymphocytes, while secondary lymphoid organs, such as the spleen and lymph nodes, facilitate immune responses. It highlights the roles of various cell types and processes, including hematopoiesis in the bone marrow and T cell maturation in the thymus.

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)

18. THANK YOU