BSC2086 A&P II Exam #3 Study Guide 1 Lesson 11: The Lymphatic System Lymphatic System and Immunity • Pathogens: Microscopic organisms that cause disease o Viruses o Bacteria o Fungi o Parasites • Immune System o Immunity: The ability to resist infection and disease ALL body cells & tissues involved in production of immunity, NOT just the lymphatic system o Two (2) Main Types of Defenses: Nonspecific Defenses: Block or attack any potential infectious organism • Cannot distinguish one attack from another Specific Defenses: Identify, attack, and develop immunity to a specific pathogen • Lymphocytes • Lymphatic System – protects us against disease o Lymphatic system cells respond to: Environmental pathogens Toxins Abnormal body cells (i.e cancers) Structures of Body Defenses • Organization of Lymphatic System: o Lymph: A fluid similar to plasma, but without plasma proteins o Lymphatic Vessels (Lymphatics): Carry lymph from peripheral tissues to the venous system o Lymphoid Tissues & Lymphoid Organs o Lymphocytes, phagocytes, and other immune system cellsBSC2086 A&P II Exam #3 Study Guide 2 • Function of lymphatic system = to produce, maintain, and distribute lymphocytes o Lymphocytes detect problems & travel to site of injury or infection • Lymphocyte Production o Lymphocytes are produced by lymphoid stem cells In lymphoid tissues (i.e. tonsils) In lymphoid organs (i.e. spleen, thymus) In red bone marrow • Lymphocyte Circulation – from blood to interstitial fluid through capillariesBSC2086 A&P II Exam #3 Study Guide 3 o Returns to venous blood through lymphatic vessels • Circulation of Fluids – from blood plasma, to lymph, and back to venous system o Transports hormones, nutrients, & waste products • Lymphatic Vessels: Vessels that carry lymph o Lymphatic system begins with lymphatic capillaries – smallest vessels Differ from blood capillaries in four (4) ways: • Start as pockets rather than tubes (dead ends) • Larger diameters • Thinner walls • Flat/irregular outline in sectional view Endothelial cells loosely bound together with overlap • Overlap acts as one-way valve o Allows fluids, solutes, viruses, and bacteria to enter o Prevents return to intercellular space o Edema of tissue causes overlapping endothelial cells to separate, allowing fluid into the lymphatic capillaries • Lymph Flow – from lymphatic capillaries to larger lymphatic vessels containing one-way valves o Lymphatic vessels travel with veins o Transports lymph to: Right Lymphatic Duct – collects lymph from the right side of the body superior to the diaphragm Thoracic Duct (left) – collects lymph from the body inferior to the diaphragm and from the left side of the body superior to the diaphragm • Connected to subclavian vein to combine with venous return o Lacteals: Special lymphatic capillaries in small intestine Transport lipids (absorbed) from digestive tractBSC2086 A&P II Exam #3 Study Guide 4 • Lymphedema: Severe swelling caused by blockage of lymph drainage from a limb o Interferes with immune system function o Toxins and pathogens accumulate in swollen area Can overwhelm local defenses without triggering immune system o If persistent, connective tissue loses elasticity and swelling becomes permanent • Lymphocytes o Make up 20-30% of circulating leukocytes o Most are stored, NOT circulating o Types of Lymphocytes: T Cells B Cells NK Cells o T Cells: Thymus-dependent Make up 80% of circulating lymphocytes Main types: • Cytotoxic T (TC) Cells: Produce cell-mediated immunity o Attack cells that have been infected by viruses • Memory T Cells: Remain in body to “remember” immunity o Formed in response to exposure to foreign substance • Helper T (TH) Cells: Stimulate function of T & B cells • Suppressor T (TS) Cells: Inhibit function of T & B cellsBSC2086 A&P II Exam #3 Study Guide 5 o B Cells: Bone marrow-derived Responsible for humoral immunity Make up 10-15% of circulating lymphocytes Differentiate into plasma cells that produce & secrete antibodies (immunoglobin proteins) • Antigens: Targets that identify any pathogen or foreign compound • Immunoglobulins (Antibodies): Binding of a specific antibody to its specific target antigen initiates antibody-mediated immunity – chain of events that destroys the target compound or organism o Natural Killer (NK) Cells (Large Granular Lymphocytes) Make up 5-10% of circulating lymphocytes Responsible for immunological surveillance • Attack foreign cells, virus-infected cells, and cancer cellsBSC2086 A&P II Exam #3 Study Guide 6 o Lymphocytes wander through tissues Enter blood vessels or lymphatics for transport Can survive many years • 80% live up to 4 years, some last more than 20 years o Lymphopoiesis – lymphocyte production Involves: • Bone marrow • Thymus • Peripheral lymphoid tissues Hemocytoblasts in bone marrow divide into two (2) types of lymphoid stem cells Lymphoid Stem Cells • Group 1 o Remain in bone marrow & develop with help of stromal cells – produce the cytokine interleukin-7 to promote B cell differentiation o Produces B cells & natural killer cells • Group 2 o Migrates to thymus o Produces T cells in environment isolated by blood-thymus barrierBSC2086 A&P II Exam #3 Study Guide 7 T Cells & B Cells… • Migrate through body to defend peripheral tissues • Retain their ability to divide o Produces daughter cells of the same type o This ability is essential to immune system function • Lymphoid Tissues: Connective tissues dominated by lymphocytes • Lymphoid Nodules: Areolar tissue with densely packed lymphocytes o Germinal center contains dividing lymphocytes Located in the central zone of the nodule o Distribution: Lymph nodes, spleen, respiratory tract (tonsils) Along digestive, urinary, and reproductive tractsBSC2086 A&P II Exam #3 Study Guide 8 • Mucosa-Associated Lymphoid Tissue (MALT): Lymphoid tissues associated with the digestive system o Protects epithelia of the digestive, reproductive, urinary, and respiratory organ systems o Aggregated Lymphoid Nodules (Peyer’s Patches): Clustered deep to intestinal epithelial lining o Appendix (Vermiform Appendix) – contains a mass of fused
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