Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 23: Lymphatic System Anatomy & Physiology

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Overview of the Lymphatic System Two most important functions—maintain fluid balance in the internal environment and immunity; a third function is to collect absorbed fat from the intestines and transport it to the systemic veins Lymph vessels act as “drains” to collect excess tissue fluid and return it to the venous blood just before it returns to the heart (Figure 23-1) 2

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Overview of the Lymphatic System Lymphatic system—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 23-2) 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 4

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Lymph and Interstitial 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 6

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Lymph and Interstitial Fluid 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 7

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Lymphatic Vessels Distribution of lymphatic vessels (lymphatics) (Figures 23-2 and 23-3)  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 8

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Lymphatic Vessels Distribution of lymphatic vessels (lymphatics) (cont)  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 the left subclavian vein; thoracic duct originates as the cisterna chyli (chyle cistern) 10

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Lymphatic Vessels Structure of lymphatic vessels (Figure 23-4)  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  One-way valves are present every few millimeters in large lymphatics and even more frequently in smaller lymphatics 11

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 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 13

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 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 23- 5). The lymphatic pump  Lymphokinesis—the movement (flow) of lymph; can be visualized in a lymphangiogram (Figure 23-6)  Lymph moves through the system in the right direction because of the large number of valves 14

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Circulation of Lymph The lymphatic pump (cont)  Breathing movements and skeletal muscle contractions (Figure 23-7) establish a fluid pressure gradient, as they do with venous blood  Other factors, such as IF pressure, also drive lymphokinesis (Figure 23-8)  Lymphokinetic actions—activities that result in a central flow of lymph 17

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Lymph Nodes Structure of lymph nodes  Lymph nodes are oval-shaped structures enclosed by a fibrous capsule (Figure 23-9)  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 23-10)  Trabeculae extend from the covering capsule toward the center of the node  Cortical and medullary sinuses are lined with reticuloendothelial cells capable of phagocytosis 20

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Lymph Nodes Locations of lymph nodes  Most lymph nodes occur in groups  Groups with greatest clinical importance are preauricular lymph nodes, submental and submaxillary groups, and superficial cervical, superficial cubital, axillary, iliac, and inguinal lymph nodes (Figures through 23-13) 23

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Lymph Nodes Functions of lymph nodes—perform two distinct functions  Defense functions Filtration  Mechanical filtration—physically stopping particles from progressing further in the body  Biological filtration—biological activity of cells destroys and removes particles 27

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Lymph Nodes Functions of lymph nodes (cont)  Defense functions (cont) 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 and 23-15)  Hematopoiesis—lymphoid tissue is the site for the final stages of maturation of some lymphocytes and monocytes 28

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 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 Distribution of lymphatics in the breast (Figure 23-16)  Drained by two sets of lymphatic vessels Lymphatics that drain the skin over the breast with the exception of the areola and nipple Lymphatics that drain the underlying substance of the breast, as well as the skin of the areola and nipple 31

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Lymphatic Drainage of the Breast Distribution of lymphatics in the breast (Figure 23-16)  Superficial vessels converge to form a diffuse, cutaneous lymphatic plexus  Subareolar plexus—located under the areola surrounding the nipple; where communication between the cutaneous plexus and large lymphatics that drain the secretory tissue and ducts of the breast occurs 33

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Lymphatic Drainage of the Breast Lymph nodes associated with the breast  More than 85% of the lymph from the breast enters the lymph nodes of the axillary region  Remainder of lymph enters lymph nodes along the lateral edges of the sternum 34

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Tonsils Form a broken ring under the mucous membranes in the mouth and back of the throat—the pharyngeal lymphoid ring (Figure 23-17)  Palatine tonsils—located on each side of the throat  Pharyngeal tonsils—located near the posterior opening of the nasal cavity  Lingual tonsils—located near the base of the tongue  Tubal tonsils—located near the openings of the auditory (eustachian) tubes 35

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Tonsils Protect against bacteria that may invade tissues around the openings between the nasal and oral cavities; bacteria are trapped in tonsillar crypts and put in close contact with immune system cells 37

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Thymus Location and appearance of the thymus (Figure 23-18)  Primary organ of lymphatic system  Single, unpaired organ located in the mediastinum, extending upward to the lower edge of the thyroid and inferiorly as far as the fourth costal cartilage  Thymus is pinkish gray in childhood; with advancing age, becomes yellowish as lymphoid tissue is replaced by fat 38

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Thymus Structure of the thymus  Two 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 40

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. 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 23-19) 41

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Spleen Location of the spleen—in the left hypochondrium, directly below the diaphragm, above the left kidney and descending colon, and behind the fundus of the stomach (Figures 23-2 and 23-20) Structure of the spleen (Figure 23-21)  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; made up of cords of WBCs and related cells surrounded by sinusoids 43

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Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Spleen Functions of the spleen  Defense—macrophages lining the sinusoids of the spleen remove microorganisms from the blood and phagocytose them  Tissue repair—the spleen holds a reservoir of monocytes that migrate in a large mass to sites of injury to help with tissue healing and repair  Hematopoiesis—monocytes and lymphocytes complete their development in the spleen 46

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Spleen Functions of the spleen (cont)  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 47

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cycle of Life: Lymphatic System Dramatic changes throughout life Organs with lymphocytes appear before birth and grow until puberty Postpuberty  Organs atrophy through late adulthood Shrink in size Become fatty or fibrous  Spleen—develops early, remains intact 48

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. Cycle of Life: Lymphatic System Overall function maintained until late adulthood  Later adulthood Deficiency permits risk of infection and cancer Hypersensitivity—likelihood of autoimmune conditions 49

Mosby items and derived items © 2013, 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. The Big Picture: The Lymphatic System and the Whole Body Lymphatic system drains away excess water from large areas Lymph is conducted through lymphatic vessels to nodes, where contaminants are removed Lymphatic system benefits the whole body by maintaining fluid balance and freedom from disease 50