Understanding Lymph Nodes: Histology, Zones, And Immune Functions

Understanding Lymph Nodes: Histology, Zones, And Immune Functions

Histology of Lymph Node
Answer:

• They are small beanshaped structures scattered along the course of lymphatic vessels
• Its concavity constitute a hilum for entry & exit of blood vessels
• Histology of medium sized artery It consists of:
  1. Connective tissue framework
     • Interstitial spaces of it is filled with lymphocytes & other cells
     • Lymph node is surrounded by a capsule
     • It consists of mainly collagen fibres & some elastic fibres & smooth muscle
     • Remaining part of lymph node contains reticular fibres
     • Each lymph node is divided into lobules by septa or trabeculae that extendsfrom capsule into the node
  2. Cells
     1. Lymphocytes
        • Lymphocytes present in blood are of two types
          1. BLymphocytes
             • It divides rapidly
             • Matures into plasma cells
             • Functions:
             • Remain in lymph node as memory cells & produce plasma cells
             • Return to blood stream via lymph
             • Concern with humoral immunity
          2. T-Lymphocytes
             • Present in between the lymphatic nodules
             • Concern with cellmediated immunity
     2. Fibroblasts
        • Spindle shaped cell
        • Present along reticular fibres
     3. Macrophages
        • Present in lymph sinuses & around germinal center
        • More in medulla than in cortex
        • Help in phagocytosis
     4. Endothelial cells
        • Present lining the blood vessels of lymph node
     5. Pericytes & smooth muscle cells
        • Present around the blood vessels

Histology of medium sized artery Zones:

1. Cortex
   • Outermost zone
   • Contains densely packed lymphocytes
   • It is darkly stained
   • Several rounded areas called lymphatic follicles or nodules are present
   • Each nodule contains a germinal center surrounded by densely packed lymphocytes
2. Medulla
   • It is lighter zone surrounding cortex
   • Contains fewer lymphocytes
   • These lymphocytes are arranged in the form of branching

2. Histology of medium sized artery Lymphocytes

• Present in the cortex of each lobules as densely packed
• Less densely packed in medulla of lobule

3. Histology of medium sized artery Macrophages

• Placed subjacent to the capsule at corticomedullary junction & in the medulla
  Functions:
• Phagocytosis
• Deeper cells are dendritic

4. Histology of medium sized artery Corpuscles of Hassall

• They are small rounded cells
• Present in medulla