Histology Lec 3 - Lymphatic System PDF

# Lymphatic System ## Lymphatic Organs - Lymph nodes - Spleen - Tonsils - Thymus ## Lymph Vessels - Formed of: - Blood plasma - Lymphocytes - Antibodies ## Description of Lymphatic System and its Organs - The lymph is filtered through the cortical and medullary sinuses. - The spleen...

# Lymphatic System ## Lymphatic Organs - Lymph nodes - Spleen - Tonsils - Thymus ## Lymph Vessels - Formed of: - Blood plasma - Lymphocytes - Antibodies ## Description of Lymphatic System and its Organs - The lymph is filtered through the cortical and medullary sinuses. - The spleen is the largest lymphoid organ in the body. - The spleen filters blood, storing erythrocytes, phagocytosing damaged and aged red blood cells. - The spleen acts as a site of proliferation of B and T lymphocytes and the manufacture of antibodies - The spleen differs from other lymphoid organs in that it lacks cortex and medulla - The spleen is present in the abdomen. - The spleen is divided into regions: - Red pulp - White pulp ## Stroma - Capsule - Composed of dense irregular collagenous connective tissue - Has elastic fibers and smooth muscle cells - Thicker at hilum - Sepra (trabecula) - Network of reticular fibers - Collagenous connective tissue that forms the frame work of the spleen - Attached to the internal aspect of the capsule ## Parenchyma - White Pulp - Include the central artery - Red Pulp - Splenic cords - Blood sinusoid (Billroth cords) ## Histology of Spleen - **Splenic nodules (white pulp)** - Central zone (B-lymphocytes) - Red pulp (RBCs and plasma cells) - Cords of Billroth - **Capsule** - Trabeculae - **Central artery** - **Perioterial lymphoi sheath (PALS)** - Contains T-lymphocytes - **Splenic marginal aterry** - Arteriolar loopes - Receive B lymphocytes - Macrophage ## Additional Details - **Nerves, blood and lymph vessels enter and leave the spleen at its hilum** - **Intraperitoneal organ, covered by a simple squamous epithelium (peritonum)** ## Anatomy of White Pulp - Includes the central artery and lymphatic nodules - Lymphatic nodes consist mainly of B lymphocytes. - Antigen-presenting cells and macrophages are also present in the white pulp. ## Anatomy of Marginal Zone - Region between red and white pulps - Receives capillary loops from the central artery, which drain into small sinusoids located at the periphery of the lymphatic nodules. - Is the first site where blood contacts the splenic parenchyma and is richly supplied by avidly phagocytic macrophages and antigen-presenting cells. - Is the site where T and B lymphocytes enter the spleen prior to becoming segregated to their specific locations within the organ. ## Anatomy of Red Pulp - Is composed of an interconnected network of sinusoids supported by a loose type of reticular tissue consisting of splenic cords (Cords of Billroth). ## Anatomy of Sinusoids - Their endothelial cells are long and fusiform, with relatively large intercellular spaces. - Outside the endothelium are circumferentially arranged "ribs" composed of filamentous material and containing a few collagen fibrils. - "Ribs" appear to constitute a thick, discontinuous basal lamina supported by reticular fibers. ## Anatomy of Splenic Cords - Contain plasma cells, reticular cells, various types of blood cells and macrophages enmeshed within the spaces of the reticular fiber network. - Processes of the macrophages enter the lumina of the sinusoids through the large intercellular spaces between the sinusoidal lining cells.