MHS 231 Lymph Nodes

Lymph Nodes

Lymph nodes are small organs interposed along lymphatic vessels.

• Capsule - dense connective tissue enclosing the node.
  • Subcapsular Sinus - space underneath the capsule that receives lymph from afferent lymphatic vessels.
• Cortex - outer region of the node.
  • Outer Cortex - region adjacent to the capsule.
    • Primary Nodules - spherical accumulations of B cells (without a germinal center).
    • Secondary Nodules - spherical accumulations of B cells with a germinal center where B cells differentiate into plasma cells.
  • Inner Cortex (paracortex) - region between the outer cortex and the medulla that is free of nodules.
    • Thymus-dependent Cortex - this region contains most of the T cells in a node.
    • High Endothelial Venules (HEV; #1,#2,#3) - venules with unusually tall endothelial cells through which lymphocytes in the blood enter the node.
• Medulla - inner part of the node. The cells are arranged in cords surrounded by sinuses.

The macrophages in this specimen contain large amounts of brown lipofuscin pigment. This helps in their identification in the subcapsular sinus and the medulla.