Tissues & Organs
Tissues & Organs
Diffuse Lymphoid Tissue
Found in
Mucosa of gastrointestinal, respiratory, and urinary tracks
Cellular Component
Lymphocytes, macrophages, reticular cells
Connective Tissue
Reticular fibres (type III collagen)
Gut-Associated Lymphoid Tissue
Organized lymphoid tissue is found throughout the gastrointestinal system except in the stomach. They are referred to as GALT. The largest lymphoid aggregates are found in the ileum and are called Peyer’s Patches.
Lymph Nodule
Key IDs
Primary Lymph Nodule | uniform colour
Secondary Lymph Nodule | 2 distinct colours (primary nodule and germinal centre)
Ileum
Lymphoid nodules found in the ileum are called Peyer’s Patches. These follicles often contain germinal centres where mature B cells proliferate and differentiate. Although too far to see, the simple epithelium of the epithelial cells found in the mucosa of lymphoid tissues facilitate antigen sampling in the lumen.
Rabbit Appendix
Large masses of lymphoid tissue are present in the mucosa and submucosa as shown by the dark purple stain. The lymphoid tissue forms follicles containing germinal centres. Lymphocytes heavily infiltrate this area.
Lymph Node
Found
Throughout body along major lymphatic vessels; neck, axilla, groin
Cellular Component
T & B cells, plasma cells, APCs, macrophages, reticular cells
Connective Tissue
Capsular layer | dense irregular collagenous connective tissue
Stroma | reticular fibres (type III collagen)
Cortex | dense irregular type I collagen
Paracortex | thymus-dependent zone and HEVs (simple cuboidal epithelium)
Medulla | loose connective tissue
Lymph Node
The outer part of the lymph node is highly cellular and is the cortex, while the medulla is the inner part and is less cellular. The cortex houses follicles which can be primary of secondary (germinal centre) lymphoid nodules. The presence of germinal centres indicates that an active immune response is underway as B cells are actively responding and proliferating. Note the characteristic reticular framework of the lymph node.
Lymph Node
Closer look at the lymph nodules inside the lymph node. Be able to differentiate between primary and secondary follicles. You can also see part of the collagenous capsule which surrounds the lymph node.
Spleen
Cellular Component
T & B cells, APCs, macrophages, reticular cells
Connective Tissue
Capsular Layer | dense irregular collagenous connective tissue with type I collagen and SMC
Stroma | reticular fibres (type III collagen)
White Pulp & Marginal Zone | PALs, trabeculae
Key ID | blood vessel passing through lymph nodule
Red Pulp | splenic sinuses and cords (loose network of reticular fibres and reticular cells)
Spleen
The white pulp consists of lymphoid aggregations (dark purple) while the red pulp (bulk of the organ) is highly vascular tissue. The thin fibroelastic cartilage is shown, from which the trabeculae descend into the parenchyma. Note, again, the reticular tissue framework which is also seen in the lymph node.
Spleen
A closer look at a central arteriole passing through the splenic nodule.