LYMPHOID

ORGANS

Assoc. Prof. Dr. Karim Al-Jashamy

MSU/IMS 2010

Lymphoid Tissue

Lymphoid tissue is CT with rich supply of

lymphocytes

Exists free within regular CT or is surrounded

by capsules.

Very little cytoplasm so stain dark blue with

H&E.

Rich network of reticular fibrils produced by

fibroblast whose many processes rest on fibrils.

Lymphatic System

Lymphatic Capillaries

Lymph Node

Structure of Lymph Node

Lymph Nodes

Functions include:

Filtration of particles and microorganisms to keep

them out of general circulation.

Interaction of circulating antigens in lymph with

lymphocytes to initiate immune response.

Activation, proliferation of B lymphocytes and

antibody production.

Activation, proliferation of T lymphocytes.

Cells of Lymph Node

Lymphoid cells

Macrophages and other phagocytic antigen processing

cells

Lymphatic and vascular endothelial cells and

fibroblasts responsible for lymph node supporting

framework.

Lymph Node

subcapsular sinus; (4) intermediate sinus; (5) medullary cords; (6) medullary

sinus; (7) trabecula.

(

Section of a lymph node showing

the cortex and the medulla

1 Capsule; 2 lymphoid nodule

with germinative center, Trabecula

Medulla of Lymph Node

Lymphocytes predominate

Medullary sinuses

Medullary cords

LYMPH NODE

Stained with H&E

1 - cortex

2 - paracortical zone

3 - medulla

4 - medullary cords

5 - lymphoid follicle of the

cortex

6 - capsule

7 - subcapsular sinus

8 - cortical sinus

9 - medullary sinus

Medullary sinus of a lymph node containing reticular cells with long

processes and elongated nuclei, macrophages, and many lymphocytes. (1)

Macrophage; (2) reticular cell; (3) trabecula. H&E stain. High

magnification.

Spleen

Largest accumulation of lymphoid tissue

Abundant phagocytic cells—defense against

antigens in blood

Site of destruction of aged erythrocytes.

Production site of activated lymphocytes which

are delivered to the blood.

THUS, an important blood filter and antibody-

forming organ.

Spleen

Spleen

Spleen

Lymphoid Nodule

1. Germinative Center

2. Central artery

Tonsil

Tonsils are lymphoid structures located in the mucosa

of the tongue, palate, and pharynx which provide sites

where immune surveillance cells (lymphocytes) can

encounter foreign antigens enter the body through the

mouth or nose.

Each tonsil consists of an epithelial crypt (invaginated

pocket) surrounded by dense clusters of lymph nodules,

each with a germinal center where lymphocytes

proliferate.

The nodules are embedded in a mass of diffuse

lymphoid tissue that consists of lymphocytes migrating

to and from the germinal centers.

The epithelium lining the

crypt corresponds with that

on the adjacent surface --

stratified squamous in the

tongue and palate, or

Pseudostratified Columnar in

the pharynx.

In either case, the epithelium may be heavily

infiltrated with lymphocytes, and the crypt may be filled

with lymphocytes and other debris

PALATINE TONSIL

1 - lymphoid follicle

2 - diffuse lymphoid tissue

3 - crypt

4 - epithelium of the oral cavity musosa

6 - submucosa of the inner cover of oral cavity forms

hemi-capsule of the tonsil

Thymus

THYMUS (lobule)

H&E

1 - cortex

2 - medulla

3 - Hassal's corpuscle

4 - interlobular connective tissue

(septa)