1. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 20 Lymphatic System

2. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 2 Overview of the Lymphatic System Importance of the lymphatic system (Figure 20-1) Importance of the lymphatic system (Figure 20-1)  Two most important functions—maintain fluid balance in the internal environment and promote body’s immunity  Lymph vessels act as “drains” to collect excess tissue fluid and return it to the venous blood just before it returns to the heart  Lymphatic system—specialized component of the circulatory system; made up of lymph, lymphatic vessels, and isolated structures containing lymphoid tissue: lymph nodes, aggregated lymphoid nodules, tonsils, thymus, spleen, and bone marrow (Figure 20-2)  Transports tissue fluid, proteins, fats, and other substances to the general circulation  Lymphatic vessels begin blindly in the intercellular spaces of the soft tissues; do not form a closed circuit

3. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 3 Lymph and Interstitial Fluid Lymph (lymphatic fluid) Lymph (lymphatic fluid)  Clear, watery-appearing fluid found in the lymphatic vessels  Closely resembles blood plasma in composition but has a lower percentage of protein; isotonic  Elevated protein concentration in thoracic duct lymph because of protein-rich lymph from the liver and small intestine

4. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 4 Lymph and Interstitial Fluid Interstitial fluid (IF) Interstitial fluid (IF)  Complex, organized fluid that fills the spaces between the cells and is part of the ECM (extracellular matrix)  Resembles blood plasma in composition with a lower percentage of protein  Along with blood plasma, constitutes the extracellular fluid

5. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 5 Lymphatic Vessels Distribution of lymphatic vessels (lymphatics) (Figures 20-2 and 20-3) Distribution of lymphatic vessels (lymphatics) (Figures 20-2 and 20-3)  Lymphatic capillaries—microscopic blind-end vessels where lymphatic vessels originate; wall consists of a single layer of flattened endothelial cells; networks branch and anastomose freely  Lymphatic capillaries merge to form larger lymphatics and eventually form the main lymphatic trunks, the right lymphatic ducts, and the thoracic duct  Lymph from upper right quadrant empties into right lymphatic duct and then into right subclavian vein  Lymph from rest of the body empties into the thoracic duct, which then drains into left subclavian vein; thoracic duct originates as the cisterna chyli (chyle cistern)

6. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 6 Lymphatic Vessels Structure of lymphatic vessels (Figure 20-4) Structure of lymphatic vessels (Figure 20-4)  Similar to veins except lymphatic vessels have thinner walls, have more valves, and contain lymph nodes  Lymphatic capillary wall is formed by a single layer of thin, flat endothelial cells  As the diameter of lymphatic vessels increases from capillary size, the walls become thicker and have three layers  Semilunar valves are present every few millimeters in large lymphatics and even more frequently in smaller lymphatics

7. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 7 Lymphatic Vessels Functions of the lymphatic vessels Functions of the lymphatic vessels  Remove high–molecular weight substances and even particulate matter from interstitial spaces  Lacteals absorb fats and other nutrients from the small intestine

8. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 8 Circulation of Lymph From lymphatic capillaries, lymph flows through progressively larger lymphatic vessels to eventually reenter blood at the junction of the internal jugular and subclavian veins (Figure 20-5). From lymphatic capillaries, lymph flows through progressively larger lymphatic vessels to eventually reenter blood at the junction of the internal jugular and subclavian veins (Figure 20-5). Lymphatic pum p Lymphatic pum p  Lymphokinesis—the movement (flow) of lymph; can be visualized in a lymphangiogram (Figure 20-6)  Lymph moves through the system in the right direction as a result of the large number of valves  Breathing movements and skeletal muscle contractions (Figure 20-7) establish a fluid pressure gradient, as they do with venous blood  Other factors, such as IF pressure, also drive lymphokinesis (Figure 20-8)  Lymphokinetic actions—activities that result in a central flow of lymph

9. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 9 Lymph Nodes Structure of lymph nodes Structure of lymph nodes  Lymph nodes are oval structures enclosed by a fibrous capsule (Figure 20-9)  Nodes are a type of biological filter  Once lymph enters a node, it moves slowly through sinuses to drain into the efferent exit vessel (Figure 20-10)  Trabeculae extend from the covering capsule toward the center of the node  Cortical and medullary sinuses are lined with specialized reticuloendothelial cells capable of phagocytosis

10. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 10 Lymph Nodes Locations of lymph nodes Locations of lymph nodes  Most lymph nodes occur in groups  Location of groups with greatest clinical importance are submental and submaxillary groups, and superficial cervical, superficial cubital, axillary, iliac, and inguinal lymph nodes (Figures 20-11 through 20-13)  Preauricular lymph nodes located in front of the ear drain superficial tissues and skin on the lateral side of the head and face

11. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 11 Lymph Nodes Functions of lymph nodes—perform two distinct functions Functions of lymph nodes—perform two distinct functions  Defense functions Filtration Filtration  Mechanical filtration—physically stops particles from progressing further in the body  Biological filtration—biological activity of cells destroys and removes particles Phagocytosis—reticuloendothelial cells remove microorganisms and other injurious particles from lymph and phagocytose them (biological filtration) Phagocytosis—reticuloendothelial cells remove microorganisms and other injurious particles from lymph and phagocytose them (biological filtration) If overwhelmed, lymph nodes can become infected or damaged (Figures 20-14 and 20-15) If overwhelmed, lymph nodes can become infected or damaged (Figures 20-14 and 20-15)  Hematopoiesis—lymphoid tissue is site for final stages of maturation of some lymphocytes and monocytes

12. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 12 Lymphatic Drainage of the Breast Clinically important because cancer cells and infections can spread along lymphatic pathways to lymph nodes and other organs of the body Clinically important because cancer cells and infections can spread along lymphatic pathways to lymph nodes and other organs of the body Distribution of lymphatics in the breast (Figure 20-16) Distribution of lymphatics in the breast (Figure 20-16)  Drained by two sets of lymphatic vessels Lymphatics that drain skin over breast with the exception of areola and nipple Lymphatics that drain skin over breast with the exception of areola and nipple Lymphatics that drain substance of breast, as well as skin of areola and nipple Lymphatics that drain substance of breast, as well as skin of areola and nipple  Superficial vessels converge to form a diffuse, cutaneous lymphatic plexus  Subareolar plexus—located under areola surrounding nipple; where communication between cutaneous plexus and large lymphatics that drain the secretory tissue and ducts of the breast occurs

13. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 13 Lymphatic Drainage of the Breast Lymph nodes associated with the breast Lymph nodes associated with the breast  More than 85% of lymph from the breast enters lymph nodes of axillary region  Remainder of lymph enters lymph nodes along lateral edges of sternum

14. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 14 Tonsils Form a broken ring under the mucous membranes in the mouth and back of the throat—the pharyngeal lymphoid ring (Figure 20-17) Form a broken ring under the mucous membranes in the mouth and back of the throat—the pharyngeal lymphoid ring (Figure 20-17)  Palatine tonsils—located on each side of throat  Pharyngeal tonsils—located near posterior opening of nasal cavity  Lingual tonsils—located near base of the tongue Protect against bacteria that may invade tissues around the openings between the nasal and oral cavities Protect against bacteria that may invade tissues around the openings between the nasal and oral cavities

15. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 15 Thymus Location and appearance of the thymus (Figure 20-18) Location and appearance of the thymus (Figure 20-18)  Primary central organ of lymphatic system  Single, unpaired organ located in the mediastinum, extending upward to lower edge of thyroid and inferiorly as far as fourth costal cartilage  Thymus is pinkish gray in childhood; with advancing age, becomes yellowish as lymphoid tissue is replaced by fat

16. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 16 Thymus Structure of the thymus Structure of the thymus  Pyramid-shaped lobes are subdivided into small lobules  Each lobule is composed of a dense cellular cortex and an inner, less dense, medulla  Medullary tissue can be identified by presence of thymic corpuscles

17. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 17 Thymus Function of the thymus Function of the thymus  Plays vital role in immunity mechanism  Source of lymphocytes before birth  Shortly after birth, thymus secretes thymosin and other regulators, which enables lymphocytes to develop into T cells (Figure 20-19)

18. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 18 Spleen Location of the spleen—in left hypochondrium, directly below diaphragm, above left kidney and descending colon, and behind fundus of stomach (Figures 20-2 and 20-20) Location of the spleen—in left hypochondrium, directly below diaphragm, above left kidney and descending colon, and behind fundus of stomach (Figures 20-2 and 20-20) Structure of spleen (Figure 20-21) Structure of spleen (Figure 20-21)  Ovoid in shape  Surrounded by fibrous capsule with inward extensions that divide the organ into compartments  White pulp—dense masses of developing lymphocytes  Red pulp—near outer regions, made up of a network of fine reticular fibers submerged in blood that comes from nearby arterioles

19. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 19 Spleen Functions of the spleen Functions of the spleen  Defense—macrophages lining sinusoids of spleen remove microorganisms from blood and phagocytose them  Hematopoiesis—monocytes and lymphocytes complete their development in the spleen  Red blood cell and platelet destruction—macrophages remove worn-out RBCs and imperfect platelets and destroy them by phagocytosis; also salvage iron and globin from destroyed RBCs  Blood reservoir—pulp of spleen and its sinuses store blood

20. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 20 Cycle of Life: Lymphatic System Dramatic changes throughout life Dramatic changes throughout life Organs with lymphocytes appear before birth and grow until puberty Organs with lymphocytes appear before birth and grow until puberty Postpuberty Postpuberty  Organs atrophy through late adulthood Shrink in size Shrink in size Become fatty or fibrous Become fatty or fibrous  Spleen—develops early, remains intact Overall function maintained until late adulthood Overall function maintained until late adulthood  Later adulthood Deficiency permits risk of infection and cancer Deficiency permits risk of infection and cancer Hypersensitivity—likelihood of autoimmune conditions Hypersensitivity—likelihood of autoimmune conditions

21. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 21 The Big Picture: The Lymphatic System and the Whole Body Lymphatic system drains away excess water from large areas Lymphatic system drains away excess water from large areas Lymph is conducted through lymphatic vessels to nodes, where contaminants are removed Lymph is conducted through lymphatic vessels to nodes, where contaminants are removed Lymphatic system benefits the whole body by maintaining fluid balance and promoting freedom from disease Lymphatic system benefits the whole body by maintaining fluid balance and promoting freedom from disease