Describe the general architecture of the lymph node
Parenchyma
Cortex: Outer portion of the lymph node except the hilum
Superficial (Nodular) cortex
Primary nodules: Small lymphocytesSecondary nodules: Possess a germinal center
Deep cortex (Paracortex): Contains most of the T-cells (Thymus-dependent)
Medulla: Inner part of the lymph node
Medullar sinus: Opening that drains at the hilum into efferent vesselsMedullary cords: Contain reticular fibers, B lymphocytes, Macrophages, Dendritic cells, and plasma cells
Architecture of a Lymph Node
Describe the events and cells involved in ‘thymic education
Double-negative stage: T-cells do not yet express CD4 and CD8 molecules on their surface
Double-positive stage: As maturation continues, T-cells express CD4 and CD8 molecules on their surface
Type II and Type III epithelioreticular cells present T-cells with foreign and self antigens
Positive selections: Occurs in the cortex. Cells that recognize self-MHC and Self/Foreign antigens progress to the medulla: where they undergo negative selection
Negative selection: Cells that recognize self-MHC and self-Antigens are eliminated
Single-positive stage: Cells that survive negative selection either become Cytotoxic CD8+ T-cells or Helper CD4+ T-cells (By stopping expression of either CD8 and CD4 molecules on their surface)
What are Hassall’s corpuscles
Hassal’s corpuscles are isolated concentric arrangements of type IV epithelioreticular cells. These cells contain keratohyalin granules, and are joined by desmosomes; the centers show keratinization.
Their function is to produce interleukines (IL-4 and IL-7) that are necessary for the differentiation and education of T-cells.
Briefly describe the open and closed circulation of the spleen
Open circulation: Pencillar arterioles empty directly into the cords of Billroth rather than connecting to the endothelium-lined splenic sinuses. Blood entering the red-pulp seeps through the cords and is exposed to macrophages residing there.
Closed circulation: Pencillar arterioles empty directly into the splenic sinuses. The endothelium of the pencillar arterioles and that of the splenic sinuses is continuous.
