An essential part of the immune system, the lymph node is where immune cells interact with antigens and infections. The parenchyma, which is made up of several sections within the lymph node, is essential for processing and filtering lymphatic fluid. The cortex and the medulla are the two primary sections that make up a lymph node's parenchyma. Specialized structures and functions found in each of these regions support the immune response as a whole. Cortex: The cortex, which is separated into the superficial cortex and the deep cortex (paracortex), is the outermost part of the lymph node parenchyma. Superficial Cortex: This area is home to tightly packed B cell formations known as lymphoid follicles. Antibodies are produced by B cells and are vital for identifying and eliminating infections. Follicle dendritic cells are specialized cells found within follicles that deliver antigens to B cells, so triggering the immunological response. Deep Cortex (Paracortex): T cells, a different subset of immune cell essential to cellular immunity, make up the paracortex in the main. T cells are in charge of identifying aberrant or infected cells and initiating a focused immune response. High endothelial venules (HEVs), specialized blood veins found in the paracortex, enable immune cells to enter the lymph node from the bloodstream. Medulla: The medullary sinuses and cords are located in the medulla, which is the innermost part of the lymph node parenchyma. Medullary Cords: B lymphocytes, plasma cells, and macrophages are found in these lymphatic tissue cords. B cells give rise to plasma cells, which are in charge of making a lot of antibodies to support the immune response. Macrophages are phagocytic cells that consume and break down cellular waste and infections. Medullary Sinuses: These are areas lined by reticular cells and macrophages that are filled with lymphatic fluid. Prior to the lymphatic fluid leaving the lymph node, macrophages in the medullary sinuses continue to phagocytose pathogens and cellular detritus. In conclusion, the parenchyma of the lymph nodes is a dynamic, well-organized structure that is essential to the immune response. Different types of immune cells, each with particular roles aimed at identifying and removing infections to preserve general immunological health, are housed in its cortex and medulla.
