Most lymph nodes are kidney-shaped, lymphoid organs, less than 2.5 cm in length. They are enclosed in a dense fibrous connective tissue capsule (Cp). The capsule sends trabeculae (red arrow) into the stroma or parenchyma of the node, subdividing it into a number of incomplete compartments. Lymph flows from afferent lymphatic vessels into the subcapsular sinus (blue arrows). The lymph percolates through cortical sinuses until it reaches the medullary sinusoids (not visible in the image) in the central region of the node. Macrophages filter the lymph in the cortical sinuses. Portions of three lymph nodules with germinal centers (Xs) are evident in the node cortex. Actively proliferating B lymphocytes are prevalent in nodule germinal centers.
Spleen Red Pulp 400X
In the spleen, red pulp consists of splenic/venous sinuses (Ss) separated by splenic cords, or cords of Billroth (yellow arrows). Red pulp appears red because a large amount of blood fills both the splenic sinuses and the splenic cords. As arterial blood percolates through the meshwork of reticular fibers of the cords, aging RBCs (red arrow) and damaged platelets are degraded and removed. Filtration of these blood cells is one of several important hemopoietic functions performed by the spleen. Darkly stained nuclei of epithelial cells surrounding a small portion of a splenic sinus are present in the micrograph. Degraded RBCs (red arrow) are in the splenic sinus. Numerous lymphocytes, along with a variety of other cells, are scattered in the splenic cords.
Splenic Nodule White Pulp 100X
As populations of B cells accumulate in the periarterial sheath (PALS) of the splenic nodule, the central artery (red arrow) becomes eccentrically displaced. The thin marginal zone (green arrows), which is not distinguishable in the image, lies immediately exterior to the PALS. It is in this zone that lymphocytes exit tiny capillaries and first enter the splenic sinuses of the red pulp. Pink splenic cords and clear splenic sinuses can be identified in the red pulp.
Thymus Medulla 400X
The thymic medulla is the inner region of the thymus stroma. The medulla contains epithelioreticular cells (yellow arrows), loosely packed T lymphocytes (blue arrows), and thymic, or Hassall’s corpuscles (Hc). After T lymphocytes complete their development and maturation in the medulla, they become immunocompetent cytotoxic T cells, helper T cells, or gamma/delta T cells. Cytotoxic and helper T cells represent the majority of circulating lymphocytes. Gamma/delta T cells migrate from the thymus to a variety of epithelial tissues, such as the skin and mucosa of the GI tract, where they serve as the first line of defense against antigens.
OTHER IMAGES AVAILABLE WITH THE BOOK AND CD-ROM
Diffuse Lymphatic Tissue Colon 100X 400X
Primary Lymphatic Nodule Ileum 40X
Secondary Lymphatic Nodules Caecum 40X
Secondary Lymphatic Nodule Lymph Node 400X
Lymph Node 40X
Lymph Node Medullary Region 400X
Lymph Node Reticular Fibers 400X 2 Images
Palatine Tonsil Tonsillar Crypt 40X
Palatine Tonsil Lymph Nodules 40X
Palatine Tonsil Lymph Nodule Germinal Center 400X
Spleen Capsule + Stroma 40X
Spleen Capsule + Red Pulp 100X
Spleen Capsule Collagenous CT 400X
Spleen Trabecula + Splenic Pulp 100X
Spleen Trabecular Artery LS 40X 400X
Spleen Red Pulp 400X
Spleen White Pulp 100X
Splenic Nodule White Pulp 100X
Splenic Nodule Central Artery 400X
Thymus Capsule + Stroma Fetal 40X
Thymus Cortex 400X
Thymus Thymic(Hassall’s) Corpuscle 400X
Thymus Adult Involution Process 40X 2 Images
Thymus Adult Involution Process 100X
