The document discusses the structure and functions of the immune system. It describes the central lymphoid organs as the thymus and bursa of Fabricius, which educate lymphocytes. The peripheral lymphoid organs include the spleen, lymph nodes, and mucosa-associated lymphoid tissue (MALT), which filter pathogens and allow proliferation and local antigen stimulation of lymphocytes. The thymus educates T cells, while the bursa of Fabricius is responsible for B cell education in birds.

1. STRUCTURE AND FUNCTIONS
OF THE IMMUNE SYSTEM
MARYAM JAMILAH BINTI ABDUL HAMID
082013100002
IMS BANGALORE

2. LEARNING OUTCOME
 Lymphoid organs
 Central lymphoid organs
 Peripheral lymphoid organs

3. INTRODUCTION
 Lymphoid system:-
Lymphoid cells
Lymphocytes
Plasma cells
Lymphoid organs
Central (Primary)
Peripheral (Secondary)

4. Lymphoid Organs
Central Lymphoid Organs
Peripheral Lymphoid
Organs
Thymus Bursa of Fabricius Spleen
Lymph
nodes
Mucosa associated
lymphoid tissue (MALT)

5. CENTRAL LYMPHOID ORGANS
THYMUS
EMBRYOLOGY
3rd & 4th pharyngeal pouches
Mesenchymal stem cells (yolk sac, fetal liver and bone
marrow) reach thymus
Differentiate into thymic lymphoid cells (thymocytes)
Maximally relative size just before birth
Continues to grow about the twelve year
After puberty:
Spontaneous progressive involution
Functions best in early life

6. ANATOMY
 Site: behind sternum
 2 lobes surrounded by fibrous capsule
 Outer cortex: actively proliferating small lymphocytes
 Inner medulla: epithelial cells & mature lymphocytes (with
Hassall’s corpuscles)

7. MICROBIOLOGY PART
Production of thymic lymphocytes
Lymphocyte proliferation in the body
Acquire new surface antigens (‘Thy’ antigens)
Not dependent on antigenic stimulation
Prethymic lymphocytes are not
immunocompetent
‘Educated’ in thymus
Peripheral lymphatic tissue

8. BURSA OF FABRICIUS

9. BURSA OF FABRICIUS
Pouch from dorsal part of the cloaca
Day 15: becomes lymphoid organ
Near hatching: full functional ability
7-13 weeks age/puberty: involuting ( normally in
size and functional activity)
Immunocompetent 'bursal lymphocytes' or B cells
Migrate to SPLEEN (mantle, germinal follicles,
perifollicular regions) and LYMPH NODES (cortical
areas and medullary cords)

10. FUNCTION
Humoral immunity
Chicken BURSECTOMISED at hatching failed to form antibodies
when challenged with a bacterial antigen -Glick and Chang (1956)
Competence for Ig M production -early (Day 14 of embryonation)
Ig G late (about Day 21)
Birds bursectomised on Days 18 to 20 synthesize Ig M, but not Ig G
Peyer's patches; 20th week of gestation (spleen and lymph nodes)
Ig M > after birth
Ig G < 3rd month. Adequate by 2-3 years

11. PERIPHERAL LYMPHOID ORGANS
LYMPH NODES
Cortex
Medulla
Cortical follicles and medullary cords
Intermediate zone
Filter for lymph
Proliferation ofT cells and B cells
Local antigenic stimulation -ENLARGED 11

13. SPLEEN
Largest of the lymphoid organs
As a graveyard (effete blood cells)
White pulps and red pulps
Malphigian corpuscles
Germinal centre
'Mantle layer'
Marginal zone
13

14. Thymus dependent area:
 lymphatic sheath surrounds central arteriole
Bursa dependent (Thymus independent) area:
 perifollicular region
 germinal centre
 mantle layer
A systemic filter trapping circulation bloodborne foreign
particles

16. MUCOSA ASSOCIATED LYMPHOID
TISSUE (MALT)
Mucosa lining of alimentary, respiratory,
genitourinary and other lumina/surfaces that
constantly expose to numerous antigens
Rich lymphoid cells
Peyer's patches
Scattered isolated lymphoid follicles (MALT)
GALT (adenoids, tonsils to follicles of the colon)
BALT (respiratory tract) 16

17. Cells: lymphoid cells, phagocytic cells, B cells andT
cells
Predominantly IgA -from mucosa
Free traffic of antigen-specific effector
lymphocytes between various mucosal and
secretory areas; 'common mucosal or secretory
immune system'

19. Lymphoid Organs
Central Lymphoid Organs
Peripheral Lymphoid
Organs
Thymus Bursa of Fabricius Spleen
Lymph
nodes
Mucosa associated
lymphoid tissue (MALT)
CONCLUSION

20. REFERENCES
 Ananthanarayan and Paniker’s,Textbook
of Microbiology, 8th Edition
 Dir. Prof. C P Baveja,Textbook of
Microbiology, 4th Edition