LYMPHATIC SYSTEM MUDr. Hisham El Falougy, PhD. [email protected] Unencapsulated lymphoid tissue • Lymphoid follicles (nodules) • Urinary tract • Digestive tract (Peyer’s patches) • Upper respiratory tract Tonsils • Palatine • Pharyngeal • Lingual • Pharyngeal circle of Waldeyer • Tonsilla tubaria SPLEEN • Vascular and lymphoid tissue • Left hypochondrium (regio hypochondriaca sinistra) • 12 cm long, 7 cm broad (adult) • 80 – 300 g (adult) SPLEEN • Function – Phagocytosis (removal of particulate material including aging erythrocytes) – Pitting of red blood cells – Immune responses (humoral, cellular) – cytopoiesis SPLEEN • Diaphragmatic surface – Convex and smooth • Visceral surface – Gastric, renal, colic and pancreatic impressions – Hilum SPLEEN • Superior border – Convex – Separating diapgragmatic surface from gastric impression • Inferior border – Separating diapgragmatic surface from renal impression – Lower margin of 11th rib SPLEEN • Posterior extremity – Faces the vertebral column • Anterior extremity – Forms margin connecting the superior and inferior borders – Related to the left colic flexure SPLEEN • Peritoneum – Firmly adheres to the splenic capsule – Peritoneal folds (splenorenal ligament, gastrosplenic ligament) • Connective tissue trabeculae – Fibrous skeleton of spleen – Supporting delicate tissues of spleen (red pulp, white pulp) SPLEEN • Surface anatomy – Position assessed by percussion – Dull area extends over the 9th to 11th ribs – Should not go forward beyond the midaxillary line – Normal spleen is not palpable SPLEEN • Vessels and nerves – Splenic artery (branch of the coeliac artery) – In the splenorenal ligament divids into segmental branches – Enter hilum to supply splenic segments – Each artery ramifies in the trabeculae to supply parenchyma and capsule SPLEEN • Vessels and nerves – Minor veins pass from red pulp into the trabeculae – Form segmental veins leaving the hilum to the splenorenal ligament – The splenic vein drains directly into the hepatic portal vein SPLEEN • Vessels and nerves – Lymphatics drain along the trabeculae – Pass out of the hilum into lymphatic vessels accompanying the splenic artery and vein – Splenic lymph goes to pancreatosplenic and coeliac lymph nodes – Sympathetic fibers from coeliac plexus (vasomotor) – Regulates blood flow through the spleen SPLEEN • White pulp – Lymphoid tissue – B and T lymphocyte maturation an proliferation – Adventitia of arterioles within trabeculae repalced by sheath of T lymphocytes (periarteriolar lymphatic sheath) – Enlarged lymphoid follicles (Malpighian bodies) SPLEEN • White pulp – Enlarged lymphoid follicles (Malpighian bodies) – Aggregations of B lymphocytes – At terminal branches of arterioles – Germinal centers after antigen stimulation – Penicilli (terminal branches of arterioles) SPLEEN • Red pulp – Filtration device – Complex system of interconnected spaces – Phagocytic macrophages – 75% of spleen SPLEEN • Red pulp – Venous sinuses (50µm in diameter) draining into the tributaries of the splenic veins – Reticulum (fibrocellular network) – Splenic cords (of Billroth) SPLEEN • Marginal zone – Loosly arranged lymphocytes – Small aggregation of macrophages (periartetiolar macrophage sheath) • Fibrous framework – Capsule (1.5mm thick) – trabeculae SPLEEN • Splenic hypertrophy • Splenomegaly • Hymolytic diseases • splenectomy Thymus • Primary lymphoid organ • Thymus-processed lymphocytes (T lymphocytes) • Immune tolerance to the body’s own components • Neuroendocrine axis of the body Thymus • Largest up to age of 15 years • Active into old age • Pyramidal shape, red and firm in children • Thin, gray, yellow in adult • Two lobes • 20g (at birth 10-15g) Thymus • Superior and anterior inferior mediastinum • Level of 4th costal cartilage (lower border) • Extends to neck • Anterior: sternum, 4 upper ribs, sternohyoid, sternothyroid • Posterior: pericardium, aortic arch, left brachiocephalic vein, trachea Thymus • Vessels – Arteries: from internal thoracic and inferior thyroid arteries – Veins: drain to the left brachiocephalic, internal thoracic and inferior thyroid veins Thymus • Innervation – Sympathetic from stellate (cervicothoracic) ganglion – Parasymphathetic from vagus nerve – Autonomic nerves are vasomotor – Capsule of thymus recieves fibers from the phrenic nerve Thymus • Outer cortex – Densely packed cells (T lymphocytes) – Outer cortical region(subcapsular) • Inner medulla – Rich in connective tissue – Fewer lymphoid cells Thymus • Capsule – Losse connective tissue – Septa penetrate to the junction of the cortex and medulla Thymus • Cells of the mononuclear phagocyte system • Fibroblasts • Myoid cells • Lymphocyte population (thymocytes) • Thymic heamopoiesis .