The Lymph nodes are secondary lymphoid tissues. They form part of a network that filters antigens from the interstitial tissue fluid and lymph during its passage from the periphery to the thoracic duct. Thus, the Lymph nodes are the primary sites of immune response to tissue antigens.
Lymph nodes anatomy
The lymph nodes are round or kidney-shaped clusters of mononuclear cells that normally are less than 1 cm in diameter. A collagenous capsule surrounds a typical lymph node and has an indentation called the hilus where blood vessels enter and leave.
Lymph nodes typically are present at the branches of the lymphatic vessels and form part of the extensive network of lymphatic channels that extends throughout the body. Several afferent lymphatic channels that drain lymph from regional tissues into the lymph node perforate the capsule of each lymph node.
The lymph draining from the node leaves through one efferent lymphatic vessel at the hilus. The lymph from the node, in turn, empties into efferent lymphatic vessels that eventually drain into larger lymphatic channels leading eventually to the thoracic duct. The thoracic duct in turns drains into the left subclavian vein, thus returning lymph into the systemic circulation.
Lymph nodes structure
Beneath the collagenous capsule is the subcapsular sinus, into which the afferent lymphatic channels drain . This sinus is lined with phagocytic cells. Fibrous trabeculae radiate from the medulla adjacent to the hilus of the node to the subcapsular sinus, thus breaking the node into several follicles, called cortical follicles.
These trabeculae, together with the capsule and a network of reticulin fibers, support the various cellular components of the Lymph nodes and serve as the scaffolding for lymphatic spaces, namely, the subcapsular and cortical sinuses. These lymphatic spaces are continuous with medullary sinuses and the solitary efferent lymphatic channel exiting the hilus.
Lymph nodes Function
The Lymph nodes is the site where different types of lymphocytes, macrophages, and dendritic cells can interact with one another to generate an immune response to antigens carried within the lymph.
As the lymph passes across the nodes from afferent to efferent lymphatic vessels, particulate antigens are removed by the phagocytic cells and transported into the lymphoid tissue of the Lymph nodes. Abnormal cells within the lymph, such as neoplastic cells, also can be trapped within the lymph nodes.