MH 024-026 Mesentery

Lymph Nodes
(H&E)

Lymph nodes are small organs interposed along lymphatic vessels that immunologically monitor lymph.

This specimen of mesentery contains many lymph nodes (#1,#2,#3,#4).

• Capsule - dense connective tissue that surrounds the node
  • Subcapsular Sinus - space underneath the capsule that receives lymph from afferent lymphatic vessels that penetrate the capsule (lymphocytes are seen within this sinus)
  • Trabeculae - connective tissue that extends inward from the capsule.
  • Trabecular Sinuses - spaces alongside trabeculae in which lymph flows from the subcapsular sinus into the cortex.
• Cortex - outer region of the node adjacent to the capsule.
  • Nodules - spherical clusters of B lymphocytes.
• Medulla - inner part of the node.
  • Medullary Cords - irregular cords that contain plasma cells, B lymphocytes, and macrophages.
  • Medullary Sinuses - spaces surrounding medullary cords in which lymph from the cortex accumulates before exiting the node.
• Hilum - region where medullary sinuses drain into efferent lymphatic vessels and leave the node. It is also the entrance and exit for blood vessels and nerves.

Macrophages are large cells with eccentric nuclei and "foamy" cytoplasm due to numerous vacuoles. Examples are often seen individually or in clusters within nodules.

Lymph Nodes
(Azan)

Lymph nodes (#1,#2,#3) stained with azan to distinguish the stroma (or connective tissue components) from the parenchyma. Collagen fibers are restricted to the capsule and connective tissue associated with blood vessels.

Compare this slide with the previous one stained with H&E.

• Capsule - dense connective tissue (blue) enclosing the node.
  • Subcapsular Sinus - space underneath the capsule that receives lymph from afferent lymphatic vessels that penetrate the capsule.
  • Trabeculae - dense connective tissue (blue) which extends inward from the capsule.
  • Trabecular Sinuses - spaces alongside trabeculae in which lymph flows from the subcapsular sinus into the cortex.
• Cortex - outer region of the node adjacent to the capsule. It contains B lymphocytes organized into nodules.
• Medulla - inner part of the node. The cells are arranged in medullary cords surrounded by medullary sinuses.
• Hilum - region where medullary sinuses drain into efferent lymphatic vessels and leave the node. It is also the entrance and exit for blood vessels and nerves.

Macrophages are large cells with eccentric nuclei and "foamy" cytoplasm due to numerous vacuoles. Examples are often seen within nodules (#1,#2,#3).