General Histology Lecture 14 Lymph Node PDF

General Histology Lecture 14 Lymphoid system 2 Ahmed Abdul-Aziz Muhammad. PhD Lymphoid System Outline Primary lymphoid organs Bone marrow Thymus Secondary lymphoid organs Lymph nodes Spleen MALT Secondary (Peripheral) Lymphoid Organs Secondary ly...

General Histology Lecture 14 Lymphoid system 2 Ahmed Abdul-Aziz Muhammad. PhD Lymphoid System Outline Primary lymphoid organs Bone marrow Thymus Secondary lymphoid organs Lymph nodes Spleen MALT Secondary (Peripheral) Lymphoid Organs Secondary lymphoid organs act as filters that trap antigens and expose them to lymphocytes, which then go off and fight infections. There are three secondary lymphoid organs: Lymph nodes Filter lymph. Spleen Filters blood. Bonus function: destroys old red cells. Mucosa-associated lymphoid tissue (MALT) Filters antigens that try to cross mucosal surfaces. Lymphoid System Lecture Outline Introduction Primary lymphoid organs Bone marrow Thymus Secondary lymphoid organs Lymph nodes  Lymph Node Components Cortex contains round structures called lymphoid follicles (composed of B cells) Paracortex (just beneath cortex) contains T cells and high endothelial venules Medulla composed of cords (containing B cells and macrophages) and sinuses (containing reticular fibers, lymph, circulating cells and antigens) Stroma is composed of reticulin (type III collagen) fibers  Lymph Node Follicles Primary (unstimulated) follicles are composed of small, dark, mature lymphocytes. Secondary (stimulated) follicles are composed of: Germinal center: a lighter-staining central area containing larger lymphocytes Mantle zone: around germinal center; contains small, dark lymphocytes Afferent and Efferent Lymphatic Vessels Afferent lymphatic vessels Penetrate the capsule of the lymph node on the convex side. Carry lymph (with antigen and cells) from sites of infection back to the lymph nodes. Efferent lymphatic vessels Leave through the the hilum. Carry lymph (with lymphocytes) from the lymph node and return it to the blood. Lymphoid System Lecture Outline Introduction Primary lymphoid organs Bone marrow Thymus Secondary lymphoid organs Lymph nodes Spleen  Functions of the Spleen Filters blood (traps antigens) Provides a place for lymphocytes to encounter antigens and become activated Removes old red cells and platelets  Structure of the Spleen The parenchyma of spleen is called splenic pulp and consists of white pulp and red pulp. No cortex or medulla are present. Stroma consists of capsule, trabeculae, and reticular connective tissue. Hilum contains nerves, arteries and veins.  White Pulp of the Spleen White pulp consists of: Periarteriolar lymphatic sheaths (PALS) Tubule-shaped collections of T cells around arterioles Splenic follicles (nodules) Just like secondary follicles in lymph nodes, except with one more layer: the marginal zone Composed of B cells  Red Pulp of the Spleen Splenic sinuses (sinusoids) Leaky vessels lined by specialized endothelial cells (“stave cells”) and surrounded by rings of reticular fibers. Healthy red cells easily squeeze through! Old or damaged red cells get stuck Splenic cords (cords of Billroth) Located between sinuses Contain lots of macrophages, which eat old or damaged red cells Mucosa-Associated Lymphoid Tissue (MALT) Unencapsulated lymphoid tissue in mucosa and submucosa of digestive, respiratory, reproductive and urinary systems. Catches antigens as they try to cross the mucosa and get into the body. MALT in lung