The Lymph Node
Lymph nodes are encapsulated secondary lymphoid organs that act as filters for lymph, facilitating the interaction between antigens and immune cells.
Structural Organization
| Region | Key Components |
|---|---|
| Cortex | Outer region containing lymphoid follicles (B-cell zones). Primary follicles are inactive; secondary follicles contain germinal centers. |
| Paracortex | Region between follicles and medulla; primarily T-cells and High Endothelial Venules (HEVs). |
| Medulla | Inner region with medullary cords (plasma cells) and medullary sinuses. |
Lymphatic Flow & Function
- Afferent Vessels: Carry lymph into the node via the subcapsular sinus.
- HEVs: Specialized vessels in the paracortex that allow lymphocytes to exit the blood and enter the lymph node.
- Efferent Vessels: Carry filtered lymph out of the node at the hilum.
High-Yield Exam Pearl:
The paracortex is underdeveloped in patients with DiGeorge syndrome (thymic aplasia/hypoplasia), leading to a significant T-cell deficiency. In contrast, B-cell zones (follicles) are typically preserved.