DETAILED PRESENTATION ON LYMPHOID ORGANS ND HEMATOPOIESIS

1. PRESENTATION ON:
LYMPHOID ORGANS
BY- ANISHA KAZI
M.Sc SEM 1(MICROBIOLOGY)

2. INTRODUCTION
HEMATOPOIESIS
LYMPHOID PROGENITOR
MYELOID PROGENITOR
ORGANS OF IMMUNE SYSTEM
PRIMARY LYMPHOID ORGAN
SECONDARY LYMPHOID ORGAN
OTHER ASSOCIATED LYMPHOID ORGAN
MALT(MUCOSA ASSOCIATED LYMPHOID TISSUE)
GALT(GUT ASSOCIATED LYMPHOID TISSUE)
CONCLUSION
REFERENCES

3. INTRODUCTION:
 The immunity system consists of Immune cells that continuously circulate
between the Blood & Lymphoid organs.
 The Lymphatic system consists of Lymphatic organs & the circulating clear
fluid called Lymph.
 The Lymphatic system was first described in the 17th century independently
by Olaus Rudbeck & Thomas Bartholin.
 Lymphoid organs are classified into two types. They are:
1. Primary lymphoid organs.
2. Secondary lumphoid organs.

4. HEMATOPOI
ESIS:
 All blood cells arise from a type of cell called hematopoiesis stem cell (HSC). Stem
cells are cells that can differentiate into other cell types. They are self renewing,
maintaining their population level by cell division.
 In humans, hematopoiesis, the formation and development of red and white blood
cells, begins in the embryonic yolk sac during the first week of development. Yolk
sac stem cells differentiate into primitive erythroid cells that contain embryonic
hemoglobin.
 Early in hematopoiesis, a multipotent stem cell differentiates along one of two
pathways, giving rise to either a lymphoid progenitor cell or a myeloid progenitor
cell.
 Progenitor cells have lost the capacity for self renewal and are committed to a
particular cell lineage.

6. ORGANS OF THE IMMUNE
SYSTEM:
 A number of morphologically and functionally diverse organs and tissues
contribute to the development of immune responses. These organs can be
distinguished by function as the:
PRIMARY LYMPHOID ORGANS
SECONDARY LYMPHOID ORGANS
 The thymus and the bone marrow are the primary (or central) lymphoid organs
where maturation of lymphocytes takes place.
 The secondary (or peripheral) lymphoid organs include lymph nodes, the
spleen, and various mucosa associated lymphoid organs, they circulate in the
blood and lymphatic system, a network of vessels that collect fluid that has
escaped into the tissues from capillaries of the circulatory system. Ultimately,
this escaped fluid is returned to the blood.

7. PRIMARY LYMPHOID ORGANS
 Central lymphoid organs.
 These are the sites where
Leukocytes(WBCs) are generated . It
includes (i) Bone marrow & (ii) Thymus.
 The Lymphoid stem cells proliferate
,differentiate & mature.
 Contains either B-cells or T-cells.
 Site for maturation for T & B-cells.
 Differentiation of lymphocytes(eg- T-cells,
B-cells, NK-cells) is taken place here.
 Decrease in size & strength with age.
SECONDARY LYMPHOID ORGANS
 Peripheral lymphoid organs.
 These are the sites where Adaptive immune
responses are initiated.It includes (i)Spleen
(ii)Lymph node & (iii) MALT.
 The Lymphoid stem cells becomes
functional.
 Contains both B-cells or T-cell.
 Site of Cell function for T & B cells.
 Interaction of immune cells with each other
& antigen processing are taken place here.
 Increase in size with age.
PRIMARY & SECONDARY LYMPHOID
ORGANS:

8. THYMUS

9. THYMUS & ITS
FUNCTION:
 The thymus site of T- cell development and maturation, is a flat, bilobed organ
situated above the heart. Each lobe is surrounded by a capsule and divided into
lobules, which are separated from each other by strands of connective tissue called
trabeculae.
 Each lobule is organized into two compartments ,or cortex, is densely packed with
immature T- cells, called thymocytes, whereas the inner compartment, or medulla,
is sparsely populated with thymocytes.
 FUNCTION OF THYMUS:
 The main function of thymus is to release thymosin hormone that will stimulate
the maturation of T-cells.
 Failure of the thymus development shows dramatic decrease in circulating
lymphocytes of the T-cell lineage & absence of cell mediated immunity.
 Aging is accompanied by a decline in the thymic functions.

10. BONE MARROW
 Bone marrow is the site of B-cell
origin and development. Arising from
lymphoid progenitors, immature B
cells proliferate and differentiate
within the bone marrow, and stromal
cells within the bone marrow
interact directly with the B cells and
secrete various cytokines that are
required for development.
 Bone marrow B cells are the source
of about 90% of the immunoglobulins
IgG and IgA in plasma. A selection
process within the bone marrow
eliminates B cells that possess self-
reactive antibody receptors.

11. LYMPH NODE

12.  Lymph nodes are a group of small, been–shaped organ found mainly in the neck and
trunk of human body. They play vital roles in filtration of antigens and debris from
lymph and in the generation of immune responses to pathogens.
 The capsule is made up of collagen & has a sub-capsular sinus. The lymph flows into
the sinus carrying lymphocytes, Antigen processing macrophages and Dendritic cells
to the node Cortex, paracortex, & medulla.
 Morphologically, Lymph node can be divided into three roughly concentric regions: (1)
Cortex (2) Paracortex (3) Medulla.
 The outermost layer , Cortex contains lymphocytes (B-cells), Macrophages & Follicular
dendritic cells arranged in Primary follicles.
 The primary follicles enlarge into Secondary follicles, each containing a Germinal
centre. Beneath the cortex is the Paracortex, which is populated largely by T-
lymphocytes & also contains Interdigitating dendritic cells thought to have migrated
from tissues to the node.
 The innermost layer of a lymph node, the Medulla is more sparsely populated with
Lymphoid-lineage cells of those present, many are Plasma cells actively secreting
antibody molecules. The Medulla in the core of the lymph node mainly processes T-
lymphocytes.

13. SPLEEN

14.  The spleen is an organ located in the left side of the Abdominal cavity under the
Diaphragm. Similar to lymph node, it acts primarily as a blood filter.
 Old RBCs are recycled in the Spleen. Platelets and WBCs are stored in Spleen.
The Spleen also helps to fight against certain kinds of bacteria that cause
Pneumonia & Meningitis.
 It is commonly ovoid shaped and reddish brown in colour. It is surrounded by a
Capsule that extends a number of projections called, Trabeculae into the interior
to form a compartmentalized structure.
 The compartments are of two types, the (1) Red pulp & (2) White pulp which are
separated by a diffuse marginal zone.
 The splenic Red pulp consists of a network of sinusoids populated by Macrophages
& numerous RBCs & few lymphocytes. It is the site where old & defective RBCs
are destroyed & removed.

15.  The splenic White pulp surrounds the branches of splenic artery, forming a
Periarteriolar lymphoid sheath ( PALS ) populated by T-lymphocytes.
 The Marginal zone located peripheral to the PALS, is populated by Lymphocytes
& Macrophages. In the marginal zone antigen is trapped by Interdigitating-
dendritic cells which carry it to the PALS.
 The initial activation of B & T–cells takes place in T-cell rich PALS.
 FUNCTIONS :
 Spleen acts primarily as a blood filter.
 Old RBCs are recycled in the Spleen.
 Platelets and WBCs are stored in the Spleen

16. OTHER ASSOCIATED LYMPHOID ORGAN
MALT (MUCOSA ASSOCIATED LYMPHOID ORGAN):
The mucous membranes lining the digestive, respiratory, and urogenital systems have a
combined surface area of about 400 m (nearly the size of a basketball court) and are the
major sites of entry for most pathogens. These vulnerable membrane surfaces are defended
by a group of organized lymphoid tissues mentioned earlier and known collectively as
mucosal-associated lymphoid tissue (MALT).
 The functional importance of MALT in the body’s defense is attested to by it large
population of antibody-producing plasma cells, whose number far exceeds that of plasma
cells in the spleen, lymph nodes, and bone marrow combined.

17. GALT(GUT ASSOCIATED LYMPHOID TISSUE):
 The secondary lymphoid tissue associated with the respiratory epithelium is
designated bronchus associated lymphoid tissue (BALT), and that associated with
the epithelium of the digestive tract is collectively called gut associated lymphoid
tissue (GALT).
 The GALT gene provides instructions for making an enzyme called galactose-1-
phosphate uridylyltransferase. This enzyme enables the body to process a simple
sugar called galactose, which is present in small amounts in many foods.

18. CONCLUSION:
The primary and secondary lymphoid organs include thymus, bone marrow, lymph
nodes, the spleen, and various mucosa associated lymphoid organs, they circulate in
the blood and lymphatic system a network of vessels that collect fluid that has escaped
into the tissues from capillaries of the circulatory system. The main function of
lymphoid organ is to synthesize and mature T-lymphocytes, B-lymphocytes and to
maintain the immune system of the body.

19. REFERENCES
:
 Immunology by Dulsy Fatimah & N. Arumugam.
 Kuby Immunology 7th Edition.
 Fundamentals of Immunology by Willaim Paul.
 Immunology : Tizzard
 Immunology : Abbas et al.

20. THANK YOU