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14.0 The Lymphatic System.pdf
- 1. Lymphatic System Principles of Anatomy and Physiology
- 2. The lymphatic system returns fluids leaked from blood vessels back to the blood. It consists of 3 parts: Lymphatics Lymphatic vessel: Contains lymph Blood capillary Tissue cell Interstitial fluid Lymphatic capillary Lymph nodes Lymphatic System and Lymphoid Organs and Tissues
- 3. Blood capillary Tissue cell Interstitial fluid Lymphatic capillary Lymphatic vessel Lymph Lymphatic System and Lymphoid Organs and Tissues
- 4. Distribution and Structure of Lymphatic Vessels Lymph capillary Larger lymph vessel • Absent from bones, teeth, bone marrow, and the CNS • More permeable than blood capillaries: • Can take up larger molecules and particles that blood capillaries cannot • Can act as a route for pathogens or cancer cells to travel throughout the body
- 5. Distribution and Special Features Intimate association between blood capillaries and lymph capillaries Blood capillary Lymph capillary
- 6. Distribution and Structure of Lymphatic Vessels Lymph vessel endothelial cells Lymphatic capillary • Anchored to the matrix by collagen filaments • Increase in extracellular fluid (ECF) causes mini valves to open • Decrease in ECF causes mini valves to close Backflow prevention valve
- 7. Lymphatic Vessels in the GI Tract Lacteal: absorb digested fat and deliver fatty lymph (chyle) to the blood
- 8. • The larger lymphatic vessels have structures and tunics similar to those of the veins, • walls, with more internal valves. • more frequently. • Collecting vessels in the skin travel with the superficial veins, but deep vessels travel with arteries. Larger Lymphatic Vessels Lymphatic collecting vessels Lymph node Lymph duct Lymph trunk
- 9. Lymphatic Trunks Formed by union of the largest collecting vessels to drain large areas of the body Right lumbar trunk Left lumbar trunk Right bronchomediastinal trunk Left bronchomediastinal trunk Right subclavian trunk Left subclavian trunk Right jugular trunk Left jugular trunk Intestinal trunk
- 10. Larger Lymphatic Vessels Right lymphatic duct Drained by thoracic duct Drained by right lymphatic duct Thoracic duct Cysterna chyli of thoracic duct Right subclavian vein Left subclavian vein Right internal jugular vein Left internal jugular vein
- 11. The lymph system is a low-pressure system like the venous system. Lymph Transport
- 12. Lymph Transport Milking action of skeletal muscle Pressure changes in the thorax during breathing Valves to prevent backflow Pulsations of nearby arteries Contractions of smooth muscles in walls of the lymphatics Mechanisms
- 13. Physical activity increases the flow of lymph. Immobilization of the area keeps needed inflammatory material in the area for faster healing. Lymph Transport
- 14. Lymphatic System and Lymphoid Organs and Tissues Lymphoid organs and tissues provide the structural basis of the immune system by housing phagocytic cells and lymphocytes. Tonsils Thymus Spleen Lymph nodes
- 15. Lymphoid cells consist of immune system cells found in lymphoid tissue and supporting cells that form lymphoid tissue structures. Lymphoid Cells, Tissues, and Organs
- 16. Protect against antigens Examples: bacteria, toxins, viruses, mismatched RBCs, cancer cells Immune System Cells Lymphocytes: cells of the adaptive immune system T cells B cells
- 17. Immune System Cells Lymphocytes: cells of the adaptive immune system B cells produce plasma cells, which secrete antibodies T cells manage the immune response and attack and destroy infected cells
- 18. Other Lymphoid Cells Macrophages Phagocytize foreign substances and help activate T cells Dendritic cells Capture antigens, deliver them to the lymph nodes, and help activate T cells
- 19. Supporting Lymphoid Cells Reticular fibers Reticular cells Stroma: network-like support that acts as scaffolding for immune cells
- 20. Lymphoid Tissue Houses and provides proliferation sites for lymphocytes Offers surveillance vantage points for lymphocytes and macrophages as they filter through the lymph Main functions of the lymphoid tissue
- 21. Lymphoid Tissue Lymphoid tissue is largely composed of reticular connective tissue (a type of loose connective tissue): • Macrophages live on reticular fibers. • Spaces between fibers offer a place for lymphocytes to occupy when they return from patrolling the body.
- 22. 2 Types of Tissue: Diffuse Lymphoid Tissue • Loose arrangement of lymphoid cells and some reticular fibers • Found in virtually every organ of the body • Larger collections found in the lamina propria of the mucous membranes
- 23. 2 Types of Tissue: Lymphoid Follicles (Nodules) • Solid, spherical bodies consisting of tightly packed lymphoid cells and reticular fibers • Isolated patches and in the appendix Germinal centers of proliferating B cells Nodules
- 24. Lymphoid Organs 2 Functional Categories Primary lymphoid organs • Areas where T and B cells mature red bone marrow and thymus • T and B cells: originate in the bone marrow, but only B cells mature there; T cells mature in the thymus Secondary lymphoid organs • Areas where mature lymphocytes first encounter their antigen and become activated • Nodes, spleen, mucosa-associated lymphoid tissue (MALT), and diffuse lymphoid tissues
- 25. Thymus Tonsils Spleen Peyer s patches Appendix Lymph nodes Lymph Nodes 2 Main Functions Primary lymphoid organs Secondary lymphoid organs
- 26. Lymph Nodes • Lymph nodes are the principal secondary lymphoid organs of the body. • Most nodes are embedded deep in the connective tissue. • Some are closer to the body surface (inguinal, axillary, and cervical regions). Here, collecting vessels converge into trunks.
- 27. Lymph Nodes 2 Main Functions Cleansing the lymph • Lymph nodes act as lymph • Macrophages remove and destroy microorganisms and debris that enter the lymph. • Lymph nodes prevent unwanted substances from being delivered to the blood. Immune system activation • Lymph nodes offer a place for lymphocytes to become activated. • They mount an attack against antigens.
- 28. • Bean-shaped • < 2.5 cm (~1 inch) • Surrounded by an external fibrous capsule • Has capsule fibers that extend inward as trabeculae, which divide node into compartments • Two histologically distinct regions of the node: 1. Cortex 2. Medulla Structure of a Lymph Node 2 1
- 29. Cortex Superficial area of cortex
- 30. Cortex T cells
- 31. Cortex Lymphoid nodule Germinal centers: Contain dividing B cells Dendritic cells (DC): Associated with T- and B-cell activation DC present the antigen to the B cell Plasma cell Memory cell
- 32. Cortex T cell proliferates DC present the antigen to the T cell
- 33. Medulla Medullary cord: contains macrophages and antibody- producing plasma cells Artery Vein
- 34. Medulla Lymph sinus: large lymphatic capillaries Medullary cord Artery Vein
- 35. Medullary cord Artery Vein Circulation in the Lymph Nodes Afferent lymphatic vessel Subcapsular sinus Efferent lymphatic vessel Lymph sinus Medullary sinus Hilum
- 36. Artery Vein Circulation in the Lymph Nodes Afferent lymphatic vessel Efferent lymphatic vessel Afferent lymphatic vessel Afferent lymphatic vessel Afferent lymphatic vessel Afferent lymphatic vessel Hilum
- 37. Spleen Splenic vein Splenic artery Hilum Spleen • Blood-rich organ about the size of a fist • Is the largest lymphoid organ
- 38. • Site of lymphocyte proliferation and immune surveillance and response • Cleanses the blood of aged blood cells and platelets • Macrophages: remove debris Spleen Functions
- 40. Spleen 3 Additional Functions Stores breakdown products of RBCs (e.g., iron) for later reuse 1 Stores blood platelets and monocytes for release into the blood when needed 2 May be the site of fetal erythrocyte production 3
- 42. Spleen White pulp • Site where immune function occurs • Contains mostly lymphocytes on reticular fibers • Clusters around the central arteries Red pulp • Site where old blood cells and bloodborne pathogens are destroyed • Rich in RBCs and macrophages that engulf them • Composed of splenic cords (reticular tissue) that separate blood- filled splenic sinusoids (venous sinuses)
- 43. Thymus • Bilobed lymphoid organ found in the inferior neck • Extends into the mediastinum • Partially overlies the heart Thymus:
- 44. • Site of T-cell maturation • Is the most active and the largest in size during childhood • Stops growing during adolescence, then gradually atrophies • After adolescence, still produces immunocompetent cells, although more slowly Thymus
- 45. Thymus Contains rapidly dividing lymphocytes and scattered macrophages Cortex Site of regulatory T-cell development Medulla
- 46. Thymus Differences from Other Lymphoid Organs Has no lymphoid follicles 1 Stroma: 3 • Made up of epithelial cells • Provide an environment in which T lymphocytes become immunocompetent Does not directly fight antigens 2 • Functions strictly in T-lymphocyte maturation • Contains the blood-thymus barrier keeps immature T lymphocytes isolated from any antigens to prevent premature activation
- 48. • Lymphoid tissues in mucous membranes throughout the body • Protects from pathogens trying to enter the body • Found in the mucosa of the respiratory tract, genitourinary organs, and digestive tract • Tonsils • patches • Appendix Mucosa-associated lymphoid tissue (MALT): Largest collections of MALT found in: MALT
- 49. • Simplest lymphoid organs • Form a ring of lymphatic tissue around the pharynx; appear as swellings of mucosa Tonsils
- 50. Tonsils Lingual tonsil: lumpy collection of follicles at the base of the tongue Palatine tonsil: posterior end of the oral cavity (largest of the tonsils and the most often infected)
- 51. Tonsils Tubal tonsil: posterior end of the oral cavity Pharyngeal tonsil: also called adenoids
- 52. • Tonsils' function: gather and remove pathogens in food or air • Contain follicles with germinal centers and scattered lymphocytes • Not fully encapsulated Tonsils Germinal centers Stratified squamous epithelium Crypt
- 53. • The overlying epithelium invaginates, forming tonsillar crypts. • Bacteria or particulate matter enters crypts, where they are trapped and destroyed. Tonsils Germinal centers Stratified squamous epithelium Crypt
- 54. Peyer s patches • Clusters of lymphoid follicles in the wall of the distal portion of the small intestine • Also called aggregated lymphoid nodules • Structurally similar to tonsils • Functions: • Destroy bacteria • Generate memory lymphocytes
- 55. Appendix Appendix • Offshoot of the first part of the large intestine • Contains many lymphoid follicles • Location aids in functions: • Destroy bacteria, preventing them from breaching the intestinal wall • Generate lymphocytes
- 56. In a Nutshell The lymphatic system comprises the lymphatic vessels, lymph, and lymph tissues and organs, as well as immune cells. Its functions are to collect, filter, and clean interstitial fluid, and then return it to the blood. Like the veins of the circulatory system, the lymphatic vessels are a low-pressure system. The lymph organs play an integral role in the body s immune response to antigens.