Lymph nodes

The lymph nodes (commonly shortened to nodes, and known as nodus lymphoideus in TA ⁴) collectively form one of the secondary lymphoid organs.

Gross anatomy

Macroscopically, a normal lymph node is a small ellipsoid structure, approximately 0.1 to 2.5 cm in maximal length ^2,3. Nodes often possess a reniform morphology, due to an indentation in their sides named the hilum, where their blood vessels pass in and out, as well as the draining efferent lymphatic vessel ^1-3. Nodes lie in clusters adjacent to the lymphatic vessels throughout the body, which both feed and drain the nodes ³.

Each node is macroscopically divided into a peripheral cortex and central medulla.

The prenodal collecting or afferent lymphatics pass into the node through its capsule, and not at its hilum, and drain into the subcapsular sinus, a contiguous space extending around the periphery of the node (only interrupted by the hilum). From here, the lymph drains via the radially-arranged trabecular (cortical) sinuses into the central medullary sinuses (lymphatic cords), which then coalesce to emerge at the hilum as the postnodal collecting or efferent lymphatic vessel(s).

Histology

In general, a lymph node comprises a predominantly cellular peripheral cortex in which lie the spherical lymphoid follicles (or nodules). The follicle consists of a ball of lymphocytes, with an inner paler germinal center. Centrally within each node is the medulla. Additional non-follicular lymphocytes are located in both paracortical and medullary regions. The B cells are in the follicles and medulla, conversely T cells are concentrated in the paracortical and interfollicular cortical areas ¹.