Histology 7- The Lymphatic System PDF

THE LYMPHATIC (Immune) SYSTEM Dra\Amal Hussain The Lymphatic System A vessel system that connected to the circulatory system Composed of lymphatic capillaries, lymphatic vessels, lymphatic ducts and lymph nodes Its purpose is to return lymph cells (clear colorless alkaline fluid) fr...

THE LYMPHATIC (Immune) SYSTEM Dra\Amal Hussain The Lymphatic System A vessel system that connected to the circulatory system Composed of lymphatic capillaries, lymphatic vessels, lymphatic ducts and lymph nodes Its purpose is to return lymph cells (clear colorless alkaline fluid) from tissue spaces to the bloodstream The function of LS ◆ Transport proteins and fluids lost by capillary seepage back to the bloodstream ◆Protect the body against pathogens by phagocytosis and immune response ◆ Serve as the pathway for absorption of fats from small intestine into the bloodstream  lymphocytes are more common in lymphatic system-giving the system its name. ✓ B- Lymphocytes when activate by an antigen, they differentiate into plasma cells and B-memory cells. Plasma cells produce antibodies that bind to pathogens to enable their destruction(( humoral immunity). ✓ T lymphocytes): When activated by an appropriate antigen, they differentiate into:- ▪ Cytotoxic (CD+8) cells are able to kill virus infected cells or tumor cells. ▪ Helper T- (CD+4) cells are activate T& B cells. ▪ Suppressor T- cells: modulate the immune system. ▪ Memory cells This process known as cellular immunity. Immune response Accessory organs Spleen Tonsils Thymus The Spleen Located in the upper left quadrant of the abdomen The major site of erythrocyte destruction and serves as a reservoir for blood (emergency bleeding) Has essential role in the immune response and acts as a filter, removing microorganisms from blood Structure of spleen The spleen is formed of C.T stroma and parenchyma. Stroma It is the C.T frame work which includes capsule, trabeculae and reticular C.T. Parenchyma It is the soft tissue which fills the C.T frame work of the spleen, it include the white and the red pulps. white pulp A- B cell area (the lymphoid follicles) They are rounded or elongated lymphatic nodules Formed mainly of B-lymphocyte, macrophage and dendritic cells. central arteriole(small artery) is penetrates the follicle in eccentric position. Structure of spleen B- T-cell area(Peri-arterial lymphatic sheaths ) Around the central arteriole contain T-lymphocyte, macrophage and denderitic cells Red pulp or billroth cords: It is soft tissue present between the white pulps and blood sinusoids. It is formed of: Lymphocytes, Erythrocytes, Leucocytes, Plasma cells, macrophages and DC. Spleen The Tonsil ❑ Tonsils are lymphoid masses located in the depressions of the mucous membranes of the face and pharynx that filter bacteria ❑ They Include: Palatine tonsils Pharyngeal tonsils (adenoids) Lingual tonsils The Tonsil The simplest lymphoid organs, form a ring of lymphoid tissue around the pharynx Lymphoid tissue of tonsils contains follicles with germinal centers Tonsil masses are not fully encapsulated epithelial tissue overlying tonsil masses invaginates, forming blind-ended crypts Crypts trap and destroy bacteria and particulate matter Tonsil Tonsil The Thymus Located in the mediastinal cavity Plays an important role in forming antibodies and development of immune system in baby Produce T-Cell, infection fighting cells, essential for the body’s immune response It help in recognizing normal T-Cell from those attacking body’s own tissue  Structure of the Thymus Stroma : Capsule of connective tissue Incomplete septa of CT dividing the organ into two lobes and incomplete lobules which are continuous with each other. Parenchyma Cortex Outer cortex: immature T- cells (thymus cells) Inner cortex: thymus epithelial cell, macrophage, DC Medulla Mature T cells + thymus epithelial cell, macrophage, DC Thymus  Hassall's corpuscles Hassall's corpuscles (or thymic corpuscles(bodies)) are the most prominent structures in the human thymus , are found in the medulla formed from eosinophilic epithelial reticular cells arranged concentrically, and inner parts are often degenerate. Thymus SUMMARY