Lymphatic and immune systems

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  • 1. Lymphatic and Immune Systems Dragan Nikolic
  • 2. Components of the Lymphatic and Immune Systems The lymphatic system has at least three different functions: functions – Serves to maintain the fluid balance of our internal body environment – Serves as part of our immune system – Helps regulate the absorption of lipids from digested food in the small intestines and its transport to the large systemic veins
  • 3. Components of the Lymphatic and Immune Systems (Cont’d) The immune system serves as an internal “security force” to deal with abnormal cells – Repels and destroys microorganisms – Defends us from our own abnormal cells that can cause cancer
  • 4. Lymphatic System Overview of the Lymphatic System – The lymphatic system solves the problem of fluid retention in tissues • Acts as a drainage system • Collects excess tissue fluid and return it to the venous blood just before it reaches the heart – Lymphatic system is a part of the circulatory system • Consists of moving fluid derived from the blood and tissue fluid, as well as a group of vessels that return the lymph to the blood
  • 5. Lymphatic System (Cont’d) Lymphatic vessels do not form a closed system of vessels • They begin blindly in the intercellular spaces of the soft tissue of the body
  • 6. Lymphatic System (Cont’d) Lymph and Interstitial Fluid – Lymph – clear fluid found in the lymphatic vessels – Interstitial fluid – complex fluid that fills the spaces between the cells – Both fluids closely resemble blood plasma in composition – Difference is that lymph cannot clot like blood
  • 7. Lymphatic System (Cont’d) Lymphatic Vessels – Lymphatic vessels – microscopic blind-ended lymphatic capillaries; wall of each lymphatic capillary consists of a single layer of flattened endothelial cells • Networks of lymphatic capillaries branch and then rejoin repeatedly to form a network throughout the interstitial spaces of our bodies • Lymphatic capillaries merge to form larger and larger vessels until main lymphatic trunks are formed – right lymphatic duct and thoracic duct
  • 8. Lymphatic System (Cont’d) Structure of lymphatic vessels • Walls of lymphatic capillaries – Have numerous openings or clefts between the cells – As lymph flows from the thin-walled capillaries into vessels with larger diameters, the walls become thicker • Eventually these larger vessels have the three layers typical of arteries and veins • One-way valves are abundant in lymphatic vessels of all sizes
  • 9. Lymphatic System (Cont’d) Function of lymphatic vessels • Permeability of the lymphatic capillary wall permits very large molecules and even small particles to be removed from the interstitial spaces
  • 10. Lymphatic System (Cont’d) Circulation of Lymph – About 50% of the total blood protein leaks out of the capillaries into the interstitial fluid; ultimately returns to the blood by way of the lymphatic vessels
  • 11. Lymphatic System (Cont’d) The lymphatic pump • Lymph moves slowly and steadily along in its vessels into the general circulation at about 3 liters per day – Lymph flow is possible because of the large number of valves that permit fluid flow only in the general direction toward the heart – Breathing movements and skeletal muscle contraction aid in this motion
  • 12. Lymphatic System (Cont’d) Lymph Nodes – Structure of lymph nodes • Oval-shaped or bean-shaped structures; widely distributed throughout the body • Lymph nodes are linked together by the lymphatic vessels • Fibrous partitions or trabeculae extend from the covering capsule toward the center of a lymph node, creating compartments called cortical nodules • Center, or medulla, of a lymph node is composed of sinuses; separate medullary cords composed of plasma cells and B cells
  • 13. Lymphatic System (Cont’d) Locations of lymph nodes – Most lymph nodes occur in groups, or clusters – Approximately 500-600 lymph nodes are located in the body Functions of lymph nodes – Defend our bodies from invading pathogens; sites of both biological and mechanical filtration – Provide sites for the maturation of some types of lymphocytes
  • 14. Lymphatic System (Cont’d) Structure and Function of the Tonsils – Tonsils – form a protective ring under the mucous membranes in the mouth and back of the throat • Protect against bacteria that may invade tissue in the area around the openings between the nasal and oral cavities; first line of defense from the external environment – Tonsils: – Palatine – located on each side of the throat – Pharyngeal tonsils (adenoids) – lie near the posterior opening of the nasal cavity – Lingual – lie near the posterior opening of the nasal cavity
  • 15. Lymphatic System (Cont’d) Structure and Function of Aggregated Lymphoid Nodules – Also called Peyer patches – small, oval patches or groups of lymph nodes that form protective layer in mucous membrane of the small intestine • Provide protection in a spot that is potentially open to external environment via the mouth • Macrophages and other cells prevent most bacteria from penetrating the gut wall
  • 16. Lymphatic System (Cont’d) Structure and Function of the Thymus – Thymus – a primary organ of the lymphatic system • Consists of two pyramid-shaped lobes • Located in the mediastinum, extending up into the neck, close to the thyroid gland • Thymus plays a critical part in the body’s defenses against infection • Soon after birth, thymus begins secreting a group of hormones that enable lymphocytes to develop into mature T cells
  • 17. Lymphatic System (Cont’d) Structure and Function of the Spleen – Spleen – located directly below the diaphragm, just above most of the left kidney and behind the fundus of the stomach • Roughly oval in shape • Spleen has variety of functions: – Defense – Hematopoiesis – Erythrocyte and platelet destruction – Reservoir for blood
  • 18. Immune System Organization of the Immune System – Identification of cells and other particles: • Antigens – cells, viruses, and other particles with unique molecules on their surfaces – Self – Non-self – molecules on the surface of foreign or abnormal cells or particles that serve as recognition markers by our immune system – Self-tolerance – ability of our immune system to attack abnormal or foreign cells while sparing our own cells • Two categories of defense mechanisms: – Innate immunity (Nonspecific) – Adaptive immunity (Specific)
  • 19. Immune System (Cont’d) Innate (Non-specific) Immunity Phagocytosis and phagocytic cells • Phagocytosis – ingestion and destruction of microorganisms and other small particles by cells called phagocytes • Phagocytosis is classified as an innate defense • The most numerous type of phagocyte is the neutrophil; other neutrophil types include macrophages and dendritic cells (DC) Chemo-tactic factors cause neutrophils and other phagocytes to adhere to the endothelial lining of capillaries servicing the affected area – After this, phagocytic cells squeeze through the wall of a blood vessel to get to the site of the injury or infection; diapedesis
  • 20. Immune System (Cont’d) Innate (Non-specific) Immunity – Natural killer cells – provide important innate defensive functions for our bodies • Kill many types of tumor cells and cells infected by different kinds of viruses • Produced in the red bone marrow and make up about 15% of the total lymphocyte number • Recognize markers on surface membrane of invading or defective cells
  • 21. Immune System (Cont’d) Adaptive immunity – involves mechanisms that program the body to recognize specific threatening agents; specific agents immunity • Primary types of cells involved in innate immunity: – Epithelial barrier cells – Phagocytic cells – Natural killer (NK) cells • Primary types of cells involved in adaptive immunity: – T cells – B cells
  • 22. Immune System (Cont’d) Adaptive immunity – body’s third line of defense; provided by two different types of lymphocytes • Two major classes of lymphocytes: – B lymphocytes (B cells) – T lymphocytes (T cells) • B cells produce molecules called antibodies that attack the pathogens or direct other cells, such as phagocytes, to attack them; antibodymediated immunity
  • 23. Immune System (Cont’d) B Cells and Antibody-Mediated Immunity – Diversity of antibodies – every normal baby is born with an enormous number of different clones of B cells – Classes of antibodies – five classes of immuno-globulin antibodies; identified by letter names as immunoglobulins M, E, G, A, and D (USE MNEMONIC: MEGA-D) MEGA-D • IgM – antibody that immature B cells synthesize and insert into their plasma membranes • IgG – most abundant circulating antibody; cross-placental barrier during pregnancy to give passive immunity to baby • IgA – major class of antibody in the mucous membranes of the body; also in saliva and tears • IgE – produce the major symptoms of allergies and kill parasites • IgD – small amount in blood; function unknown
  • 24. Immune System (Cont’d) Types of Adaptive Immunity – Acquired immunity – classified as either natural immunity or artificial immunity • Natural immunity – results from nondeliberate exposure to antigens • Artificial immunity – results from deliberate exposure to antigens; immunizations
  • 25. Immune System (Cont’d) Types of Adaptive Immunity – Natural and artificial immunity may be “active” or “passive • Active immunity – results when an individual’s own immune system responds to a harmful agent— regardless of how it was encountered • Passive immunity – results when immunity to a disease that has developed in another individual is transferred to an individual who was not previously immune
  • 26. References • Hill, David J., (2012) Essentials of Anatomy and Physiology, Mosby, St. Louis. ISBN 9780323085113 • Metchnikoff, Elie; Translated by F.G. Binnie. (1905). Immunity in Infective Diseases (Full Text Version: Google Books). Cambridge University Press. ISBN 68025143