Lymph Nodes

About the Lymph Nodes

Lymph nodes are small, bean shaped organs distributed along the lymphatic vessels, and the body contains several hundred of them, with major clusters in the neck, armpits, groin, chest, and abdomen. Lymph carrying fluid, debris, and microbes from the tissues enters a node through several afferent vessels, percolates through a network of sinuses lined by macrophages, and leaves through an efferent vessel. Inside, the outer cortex contains follicles rich in B lymphocytes, the deeper paracortex contains T lymphocytes, and dendritic cells present antigens from the tissues to these lymphocytes, making the nodes key meeting points for starting adaptive immune responses. When they are activated by infection, lymph nodes commonly swell and may become tender. Persistent, hard, or painless enlargement can occur in lymphomas and when cancers spread through the lymphatic system. For this reason, the sentinel lymph node, the first node draining a tumor, is often sampled in breast cancer and melanoma to assess spread.