The document summarizes several secondary lymphoid organs that are part of the peripheral immune system, including lymph nodes, spleen, tonsils, Peyer's patches, and mucosa-associated lymphoid tissue (MALT). It describes the basic structure and functions of lymph nodes, which filter lymph and allow for exposure of antigens to T and B cells. The spleen filters old red blood cells from the blood and contains white pulp with T lymphocytes. MALT includes lymphoid tissues associated with mucosal surfaces that defend against pathogens entering through various entry sites.

1. VIVEKANANDHA COLLEGE OF ENGINEERING FOR WOMEN
BY :
P
.BHUVANESHWARI
3RD B.TECH/BIOTECHNOLOGY
SECONDARY LYMPHOID ORGANS

2. THYMUS GLAND
BONE MARROW
LYMPH NODES
SPLEEN
GALT,MALT,BALT
TONSILS
SALIVARY,TEAR
IMMUNE SYSTEM STRUCTURE
CENTRAL/PRIMARY
SECONDARY/PERIPHERAL

3. LYMPH NODES:
STRUCTURE OF LYMPH NODES
The lymph nodes are small, round or
ovoid bodies (2.6 cm in length)placed
along the course of lymphatic vessel.
Lymph nodes can be divided in to
three concentric regions:
 Cortex
 Paracortex
 Medulla
The capsule is made of collagen and
has a sub capsular sinus.
The lymph flow into the sinus
carrying lymphocytes, Antigen
processing macrophages and
dendritic cells to the node Cortex,
Paracortex and medulla.

4. CORTEX:
The outermost layer, Cortex contains Lymphocytes (mostly B-cells),
Macrophages and Follicular dendritic cells arranged in Primary follicles.
The primary follicles enlarge in to Secondary follicles, each containing a
Germinal centre.
PARACORTEX:
 The paracortex region of lymph nodes are populated with T-lymphocytes and
interdigitating dendritic cells.
 In the paracortex also contain specialised blood vessels (high endothelial venules)
through which many B and T cells enter the nodes.

5. MEDULLA:
 The medulla is the innermost layer of lymph node where the
lymphocytes are arranged as medullary cords.
 The medullary cords contain antibody secreting plasma cells, B-cells and
macrophages.
 The function of medullary sinus is to drains the lymph in to the efferent
lymphatic vessels.
FUNCTIONS OF LYMPH NODES:
 Lymph nodes act as a filter for lymph(filtering interstitial fluid collected)
 Filtering this exudative fluid allows for exposure of T and B cells to a wide range of
antigen
 The exposure takes place with the aid of antigen presenting cells and dendritic cell.
 Play a important role in adaptive immunity.

8. SPLEEN:
The spleen is an organ located in the left side of the Abdominal cavity under the
diaphragm, the muscular partition between the abdomen and chest.

9.  The spleen in healthy adult is approximately 7cm (2.8 in)to 14 cm(5.5) in length.
It usually weighs between 150g and 200 g.
 The spleen is surrounded by a capsule that extends a number of projections called
Trabeculae which it forms a compartmentalized structure.
 The compartments are of two types.
Red pulp
White pulp which are separated by marginal zone
RED PULP:{Macrophages, numerous RBCs and few Lymphocytes}
Site where old and defective red blood cells are destroyed and removed.
WHITE PULP:{T-Lymphocytes}
The splenic white pulp surrounds the branches of the splenic artery forming a
Periarteriolar lymphoid sheath(PALS) populated mainly by T-lymphocytes.

12. A BOY IN THE PLASTIC BUBBLE:

13. MALT:
 The mucous membranes lining the digestive, respiratory and urogenital systems
have a combined surface area of about 400m2 and are the major sites of entry for
most pathogens.
 These vulnerable membrane surfaces are defended by a group of organized
lymphoid tissues mentioned collectively as Mucosal-associated lymphoid tissue
(MALT).
MALT
GALT BALT

14. Tonsils, Appendix and Peyer’s patches are the representative of lymphoid
tissue found in and around the mucosal epithelia.
TONSILS:
 The Tonsils play a major role in
protecting the body against Respiratory
and Gastrointestinal Infection.
 Each tonsil consists of a network of
crypts (pits) that store cells used to fight
infections.
 The tonsils contains B and T cells that
fight against infections.
 Tonsils produce antibodies against Polio,
Streptococcal pneumonia, Influenza and
numerous infection.

15. APPENDIX:
 Appendix is a blind ended tube connected to the cecum.
 The human appendix average 9 cm in length but can range from 2 to 20 cm. The
diameter of the appendix is usually between 7 and 8 cm.

17. PEYER’S PATCHES:
 Peyer’s patches are small masses of lymphatic tissue present throughout the ileum of
the small intestine.
 It is roughly egg shaped lymphatic tissue nodules that are similar to lymph nodes in
structure except that they are not surrounded by a connective tissue capsule.
 Important part of the immune system by monitoring intestinal bacteria population and
preventing the growth of pathogenic bacteria in the intestines.
 Peyer’s patches also playing an important role in trapping antigens from pathogens
and destroying them.

18. Antigen transported across mucous membrane by M cells
Activate B cells in follicle
Differentiate in to plasma cells
Secrete Ig A class of antibodies
Transported across epithelial cells
Secretary Ig A in to lumen
Interact with antigen

20. THANK YOU