Lymphatic tissues of Lymph Node
After leaving the bone marrow, cells travel in the blood stream and will pass through small bean-shaped structures called lymph nodes (LNs). LNs are usually <1 cm and found where blood and lymph vessels converge. THey often travel as a part of a neruovascular bundle with a nerve, artery, and vein.
Lymphatic tissues are responsible for filtering and processing antigens present in the lymphatic fluid as it travels through the lymph node (from the afferent vessels to the efferent vessel)
Route of lymph fluid through Sinuses
Lymph fluid passes through the afferent lymphatic vessel into the sub-capsular, aka, marginal sinus
It then travels through the cortex, (trabecular or para-trabecular sinus), to the medullary sinus
Exits medullary sinus through efferent lymphatic vessel.
From there, it is transported in the lymphatic vessels to other lymph nodes and eventually returned to the blood.
Lymph Node Anatomy:
Lymphatic tissues (B cells & T cells) are densely packed in the cortex into follicles/nodules & reside more loosely in the medulla as the medullary cords. Here we will look in further detail at the anatomy of a LN.
Reticular fibers and cells
Gives rise to trabeculae, which divide the node into sections and provide passage for blood vessels.
Afferent lymphatic vessels pierce the capsule to deliver lymphatic fluid to the node; valves promote unidirectional flow of blood into the LN (here) then exit the LN in the efferent vessel (hilum)
Lies just beneath the capsule. Divided into outer & inner cortex
Aggregations of B cells form primary follicles.
When the B cells proliferate, they produce secondary follicles, which comprise a lighter-staining germinal center surrounded by the darker-staining mantle zone (containingT cells).
The light and dark areas in a germinal center (dark zone/light zone) are due to variations in lymphocyte size:
Germinal centers = active medium-sized loosely organized (lighter-staining) lymphocytes
Mantle zone = smaller lymphocytes with condensed chromatin (darker).
In addition to lymphocytes, macrophages and follicular dendritic cells (FDC) reside within the follicles;
T cells and dendritic cells; Dendritic cells are the primary antigen-presenting cells (APC); that present microbial antigens on their surfaces to trigger T cell activation.
Sinuses and Medullary cords
Sinuses are lined by endothelial cells
Macrophages & Additional lymphocytes (plasma cells) reside in the sinuses & medullary cords
Open to the hilum
Area of indentation of the node; the efferent lymphatic vessel drains lymph from the node at the hilum.
Blood vessels also enter and exit at the hilum.
A portion of these notes were adapted and modified from the awesome medical education website, DrawItToKnowIt.com. This is a GREAT website for visual learners. Please subscribe to their website to view the complete lecture and see step by step drawings and charts.
Reference: DrawItToKnowIt.com - Lymph Nodes (Immune Response & Autoimmune disorders)
Edward Klatt. Robbins and Cotran Atlas of Pathology. 3rd ed. 2015. Chapters 1-4.