Lymph Node – Tutorial

Please read Unit 8 – Introduction to Lymphatic System Tissues prior to completing the activities in this chapter.

Introduction to Lymph Nodes

Lymph nodes are small lymphatic system organs located along lymphatic vessels that monitor lymphatic fluid for foreign antigens (immune surveillance) as it moves along lymphatic vessels from superficial tissues toward the right lymphatic and thoracic (left) lymphatic ducts.  Most lymph nodes are shaped like a tiny kidney and range between 1 mm to 25 mm in diameter.  Lymph nodes are located along lymphatic tracts all over the body but are more densely concentrated in the cervical (neck), axillary (armpit), and inguinal (groin) regions.

Each lymph node is surrounded by a fibrous connective tissue capsule with some collagen fibers extending from the outer capsule into the interior of the lymph node forming partial septa known as trabeculae.  The interior of a lymph node is packed with immune cells such as macrophages, dendritic cells, and lymphocytes held loosely in place by reticular fibers that form a mesh-like network throughout the interior of the lymph node.  Afferent lymphatic vessels drain lymphatic fluid into lymph nodes from distal tissues.  As lymphatic fluid slowly flows through the network of reticular fibers and immune cells inside the lymph node, most of foreign antigens are removed from the lymphatic fluid, some of which may trigger a greater immune response.  After lymphatic fluid flows through the interior of the lymph node it flows out of the node through an efferent lymphatic vessel that exits the node at a small indention in the capsule called the hilum.  The hilum is also the location where the artery and vein that service the lymph node enter and exit the node.

The interior of a lymph node is subdivided into regions known as the cortex, paracortex, and medulla.  Each of these regions have unique combinations of immune cells and are visibly distinct when observed under magnification.  The superficial cortex of a lymph node is dominated by spherical structures known as lymph follicles where B-lymphocytes proliferate (divide by mitosis) to produce large numbers of new B-lymphocytes.  The region of the cortex deep to the follicles is known as the paracortex.  The main type of cell that occupies the paracortex is T-lymphocytes.  The inner core of a lymph node is the medulla which contains mainly plasma cells organized into irregular shaped bunches called medullary cords.  The medullary cords are separated by open areas known as medullary sinuses that contain fewer lymphocytes.

Tutorial:  Use the image slider below to learn more about the structure and characteristics of lymph nodes. 

Microscopy:  Use the image slider below to learn how to use a microscope to study a lymph node on a microscope slide.

Tutorial:  Use the hotspot image below to learn more about gross structure of lymph nodes as viewed on a low power image. 

Tutorial:  Use the hotspot image below to learn more about detailed structure of the medulla of lymph nodes as viewed on a high power image. 

Tutorial:  Use the image slider below to study numerous examples of tissue from lymph nodes.