For medical, nursing, and physiotherapy undergraduates, and postgraduates

1. LYMPHOID SYSTEM
DR. SUNDIP CHARMODE
ASSISTANT PROFESSOR

2. LYMPHOID ORGANS
1. Lymph node
2. Spleen
3. Thymus
4. Palatine tonsil

3. LYMPH NODE

4. GENERAL STRUCTURE
• Capsule (Connective tissue)-
• Venules
• Arterioles
• Lymphatic vessels with valves
• Subcapsular (marginal) sinus
• Connective tissue (trabeculae) with trabecular vessels

5. GENERAL STRUCTURE
• Cortex – Lymphatic nodules separated incompletely by inter-nodular
connective tissue trabeculae
• Lymphatic nodule-
• Deeper staining peripheral region
• Central light staining (Germinal center)
• Paracortex – Deeper portion of lymph node. Thymus dependent
zone, occupied by ‘T cells’

6. GENERAL STRUCTURE
• Germinal center:
• Cells are loosely arranged
• Developing lymphocytes are larger
• Lighter staining nuclei with more cytoplasm
• Medulla: Anastomosing cords of lymphatic tissue (Medullary
cords), interspersed with medullary sinuses

11. SUBCORTICAL SINUS
1. Reticular cells
2. Macrophages
3. Epithelial cells
4. Small lymphocytes : Peripheral region of lymphatic nodule, dark
stained nucleus, dense chromatin, less cytoplasm

12. SUBCORTICAL SINUS
5. Medium sized lymphocytes – Germinal center, larger and light
stained nucleus, more cytoplasm
6. Lymphoblasts – Germinal center, largest round cells with less
condensed chromatin, broad band of cytoplasm, large vesicular
nucleus

14. PARACORTEX / DEEP CORTEX
• Post capillary venules
• Unusual morphology to facilitate migration of lymphocytes from
blood into lymph node
• High endothelial venule – tall cuboidal epithelium
• Several migrating lymphocytes are seen moving through the venule
wall

16. SUBCAPSULAR SINUS
• Arrangement of supporting reticular fibers – black – silver stains
• Thicker and denser collagen fibers in capsule – eosinophilic
• Capsule and Trabeculae
• Subcapsular sinus, trabecular sinus
• Medullary sinus and cords

17. SPLEEN

18. GENERAL STRUCTURE
• Dense connective tissue capsule and Trabeculae
• Within trabeculae are trabecular arteries and veins
• White pulp – numerous aggregations of lymphatic nodules
• Red pulp / Splenic pulp - diffuse cellular meshwork composed of
network of reticular fibers, splenic cords (of Billroth), venous sinuses,
pulp arteries

20. WHITE PULP
• Lymphatic nodule:
1. Peripheral zone – periarterial
lymphatic sheath – densely packed
small lymphocytes
2. Germinal centre
3. Central artery – eccentrically
placed

21. WHITE PULP

22. RED PULP
• Splenic cords – thin aggregations of
lymphatic tissue containing small
lymphocytes, associated cells,
various blood cells
• Venous sinuses
• Pulp arteries – branches of central
artery

24. PECULARITIES
1. Does not exhibit cortex and medulla
2. Venous sinuses are found in spleen
3. Does not exhibit trabecular or sub-capsular sinuses
4. Capsule and trabeculae in spleen are thicker than those in lymph
node

27. THYMUS

31. PALATINE TONSIL

32. GENERAL FEATURES
• Epithelium
• Not surrounded by connective tissue capsule
• Deep grooves – tonsillar crypts