BONE MARROW: Site of pluripotent stem cells. Those in the lymphoid lineage develop into B-cells and T-cells. T-cells are “educated” in the thymus; B-cells are “educated” in the bone marrow. –B-cells receive signals from STROMAL cells which include: fat cells, endothelial cells, fibroblasts, and macrophages.
The principal drainage system… Liquids of the circulatory system “leak out”; become interstitial fluids. The fluid which permeates connective tissue constitutes a few per cent of the total blood volume. This plasma is not actively pumped; rather it is moved by the constriction of the surrounding musculature; as such, the liquid becomes a drainage system. Valves prevent back flow. The fluids drain into progressively larger ducts and, ultimately, into the thoracic duct which returns the fluid to the circulatory system by emptying into the subclavian vein.
Lymph arrives in afferent vessels and leaves in efferent vessels. Afferent delivers Ag; efferent, Ab. Node is divided into cortex, paracortex, and medulla. Paracortex is the command center. There T-cells see Ag’s on stromal cells (interdigitating dendritic cells and macrophages); contact B-cells. B-cells migrate to cortex and into primary follicles; Ag stimulation continues with Ag- presentation on follicular dendritic cells; proliferative response transforms primary follicle into secondary follicle. Mature B-cells differentiate into plasma cells that migrate to medulla (to be away from Ag stimulating the response) Plasma cells secrete a single type of Ag-specific Ab into efferent fluids.
Red pulp: degradation and consumption of exhausted erythrocytes. White pulp: site of immunological monitoring of blood. Red and white pulp are separated by “marginal zone.” PALS (“periarteriolar lymphoid sheaths) surround blood arteries; arteries deliver blood to sinuses of the marginal zone. Ag’s are displayed on dendritic cells. PALS have follicles ( like lymph nodes ).
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