Schematic of lymph node showing lymph sinuses. A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. In the lymphatic system a lymph 2 ounces is a secondary lymphoid organ.

A lymph node is enclosed in a fibrous capsule and is made up of an outer cortex and an inner medulla. Lymph nodes become inflamed or enlarged in various diseases, which may range from trivial throat infections to life-threatening cancers. Cross-section of a lymph node with sections labelled. Lymph nodes are kidney or oval shaped and range in size from 2 mm to 25 mm on their long axis, with an average of 15 mm. Each lymph node is surrounded by a fibrous capsule, which extends inside a lymph node to form trabeculae. The substance of a lymph node is divided into the outer cortex and the inner medulla.

Lymph enters the convex side of a lymph node through multiple afferent lymphatic vessels and from there flows into a series of sinuses. Lymph nodes are present throughout the body, are more concentrated near and within the trunk, and are divided into groups. There are about 450 lymph nodes in the adult. Histology of a normal lymphoid follicle, showing dark, light, mantle and marginal zones. B cells, a paracortex of T cells, and a part of the nodule in the medulla. The medulla contains large blood vessels, sinuses and medullary cords that contain antibody-secreting plasma cells.

There are fewer cells in the medulla. The medullary cords are cords of lymphatic tissue, and include plasma cells, macrophages, and B cells. There are fewer cells in the medulla than the cortex. The medulla contains plasma cells, as well as macrophages which are present within the medullary sinuses. As part of the reticular network, there are follicular dendritic cells in the B cell follicle and fibroblastic reticular cells in the T cell cortex.

The reticular network provides structural support and a surface for adhesion of the dendritic cells, macrophages and lymphocytes. Labeled diagram of human lymph node showing the flow of lymph. These are channels within the node lined by endothelial cells along with fibroblastic reticular cells, allowing for the smooth flow of lymph. The endothelium of the subcapsular sinus is continuous with that of the afferent lymph vessel and also with that of the similar sinuses flanking the trabeculae and within the cortex. These vessels are smaller and don’t allow the passage of macrophages so that they remain contained to function within a lymph node.

There is usually only one efferent vessel though sometimes there may be two. A lymph node contains lymphoid tissue, i. The regions where there are few cells within the meshwork are known as lymph sinus. It is lined by reticular cells, fibroblasts and fixed macrophages. Diagram of a lymph node showing lymphocytes. The primary function of lymph nodes is the filtering of lymph to identify and fight infection.

In order to do this, lymph nodes contain lymphocytes, a type of white blood cell, which includes B cells and T cells. These circulate through the bloodstream and enter and reside in lymph nodes. Antigens are molecules found on bacterial cell walls, chemical substances secreted from bacteria, or sometimes even molecules present in body tissue itself. B cells acquire antigen directly from the afferent lymph. If a B cell binds its cognate antigen it will be activated. Some B cells will immediately develop into antibody secreting plasma cells, and secrete IgM. Other B cells will internalize the antigen and present it to follicular helper T cells on the B and T cell zone interface.