Lymph Node Histology
| Basic Components |
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- Overview
- Lymph Nodes are generally small, peanut-shaped organs surrounded by a fibrous capsule. The organ can be roughly divided into a cellular Cortex and a less cellular Medulla with different subtypes of lymphocytes occupying different histological regions of the lymph node.
- Lymph Node Capsule
- A collagenous capsule invests the entire lymph node and sends trabeculae into the organ's mass. These branching trabeculae usually stop short of the medulla.
- Afferent and Efferent Lymphatic Vessel
- Afferent lymphatic vessels pierce the capsule and drain antigen-rich lymphatic fluid into the organ while efferent lymphatic vessels drain filtered lymph from the medulla and out of the lymph node.
- Lymph Node Sinuses
- A branching network of sinuses are found throughout the lymph node mass as well as existing as a continuous sheet underneath the capsule. Lymph from afferent vessels travels through this network and comes into contact with surrounding immune cells. Lymph node sinuses possess a fine reticular network and are filled with macrophages and Dendritic Cells. Some of these cells may have traveled to the lymph node following ingestion of antigens in peripheral tissues while others may be actively phagocytosing antigens within the lymph as lymphatic fluids travels through the node. These cells ultimately act as Antigen Presenting Cells and enter the cortex or paracortex to induce an Adaptive Immune Response.
- Outer Cortex
- The highly cellular lymph node outer cortex largely consists of B-cells which in certain areas may be spherically arranged in lymphoid follicles. Some lymphoid follicles may contain Germinal Centers which represent B-cells proliferating in response to their recognized microbial antigen
- Paracortex
- Under the outer cortex lies the lymph node Paracortex which is composed largely of T-cells. The paracortex also possess specialized post-capillary venules, termed "High Endothelial Venules", which represent the entry point of circulating peripheral B-cells and T-cells into the lymph node.
- Medulla
- The Lymph Node Medulla is not very cellular but small cellular extensions of the cortex into the Medulla are termed the "Medullary Cords". The medullary cords are largely filled with Plasma Cells which are actively secrete antibody.