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Chapter 20Chapter 20Lymphatic SystemLymphatic System

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Overview of the Lymphatic System 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 Two most important functions—maintain fluid balance in the

internal environment and promote body’s immunityinternal environment and promote body’s immunity

Lymph vessels act as “drains” to collect excess tissue fluid and Lymph vessels act as “drains” to collect excess tissue fluid and return it to the venous blood just before it returns to the heartreturn it to the venous blood just before it returns to the heart

Lymphatic system—specialized component of the circulatory Lymphatic system—specialized component of the circulatory system; made up of lymph, lymphatic vessels, and isolated system; made up of lymph, lymphatic vessels, and isolated structures containing lymphoid tissue: lymph nodes, aggregated structures containing lymphoid tissue: lymph nodes, aggregated lymphoid nodules, tonsils, thymus, spleen, and bone marrow lymphoid nodules, tonsils, thymus, spleen, and bone marrow (Figure 20-2)(Figure 20-2)

Transports tissue fluid, proteins, fats, and other substances to the Transports tissue fluid, proteins, fats, and other substances to the general circulationgeneral circulation

Lymphatic vessels begin blindly in the intercellular spaces of the Lymphatic vessels begin blindly in the intercellular spaces of the soft tissues; do not form a closed circuitsoft tissues; do not form a closed circuit

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Lymph and Interstitial FluidLymph and Interstitial Fluid

• Lymph (lymphatic fluid)Lymph (lymphatic fluid)

Clear, watery-appearing fluid found in the Clear, watery-appearing fluid found in the lymphatic vesselslymphatic vessels

Closely resembles blood plasma in composition Closely resembles blood plasma in composition but has a lower percentage of protein; isotonicbut has a lower percentage of protein; isotonic

Elevated protein concentration in thoracic duct Elevated protein concentration in thoracic duct lymph because of protein-rich lymph from the liver lymph because of protein-rich lymph from the liver and small intestineand small intestine

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Lymph and Interstitial FluidLymph and Interstitial Fluid

• Interstitial fluid (IF)Interstitial fluid (IF)

Complex, organized fluid that fills the spaces between the Complex, organized fluid that fills the spaces between the cells and is part of the ECM (extracellular matrix)cells and is part of the ECM (extracellular matrix)

Resembles blood plasma in composition with a lower Resembles blood plasma in composition with a lower percentage of proteinpercentage of protein

Along with blood plasma, constitutes the extracellular fluidAlong with blood plasma, constitutes the extracellular fluid

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Lymphatic VesselsLymphatic Vessels

• Distribution of lymphatic vessels (lymphatics) Distribution of lymphatic vessels (lymphatics) (Figures 20-2 and 20-3)(Figures 20-2 and 20-3) Lymphatic capillaries—microscopic blind-end vessels where Lymphatic capillaries—microscopic blind-end vessels where

lymphatic vessels originate; wall consists of a single layer of lymphatic vessels originate; wall consists of a single layer of flattened endothelial cells; networks branch and anastomose freelyflattened endothelial cells; networks branch and anastomose freely

Lymphatic capillaries merge to form larger lymphatics and Lymphatic capillaries merge to form larger lymphatics and eventually form the main lymphatic trunks, the right lymphatic ducts, eventually form the main lymphatic trunks, the right lymphatic ducts, and the thoracic ductand the thoracic duct

Lymph from upper right quadrant empties into right lymphatic duct Lymph from upper right quadrant empties into right lymphatic duct and then into right subclavian veinand then into right subclavian vein

Lymph from rest of the body empties into the thoracic duct, which Lymph from rest of the body empties into the thoracic duct, which then drains into left subclavian vein; thoracic duct originates as the then drains into left subclavian vein; thoracic duct originates as the cisterna chyli (chyle cistern)cisterna chyli (chyle cistern)

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Lymphatic VesselsLymphatic Vessels

• Structure of lymphatic vessels (Figure 20-4)Structure of lymphatic vessels (Figure 20-4)

Similar to veins except lymphatic vessels have thinner walls, Similar to veins except lymphatic vessels have thinner walls, have more valves, and contain lymph nodeshave more valves, and contain lymph nodes

Lymphatic capillary wall is formed by a single layer of thin, flat Lymphatic capillary wall is formed by a single layer of thin, flat endothelial cellsendothelial cells

As the diameter of lymphatic vessels increases from capillary As the diameter of lymphatic vessels increases from capillary size, the walls become thicker and have three layerssize, the walls become thicker and have three layers

Semilunar valves are present every few millimeters in large Semilunar valves are present every few millimeters in large lymphatics and even more frequently in smaller lymphaticslymphatics and even more frequently in smaller lymphatics

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Lymphatic VesselsLymphatic Vessels

• Functions of the lymphatic vesselsFunctions of the lymphatic vessels

Remove high–molecular weight substances and Remove high–molecular weight substances and even particulate matter from interstitial spaceseven particulate matter from interstitial spaces

Lacteals absorb fats and other nutrients from the Lacteals absorb fats and other nutrients from the small intestinesmall intestine

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Circulation of Lymph Circulation of Lymph

• From lymphatic capillaries, lymph flows through progressively From lymphatic capillaries, lymph flows through progressively larger lymphatic vessels to eventually reenter blood at the larger lymphatic vessels to eventually reenter blood at the junction of the internal jugular and subclavian veins (Figure 20-5).junction of the internal jugular and subclavian veins (Figure 20-5).

• Lymphatic pumLymphatic pumpp Lymphokinesis—the movement (flow) of lymph; can be visualized in a Lymphokinesis—the movement (flow) of lymph; can be visualized in a

lymphangiogram (Figure 20-6)lymphangiogram (Figure 20-6)

Lymph moves through the system in the right direction as a result of the Lymph moves through the system in the right direction as a result of the large number of valveslarge number of valves

Breathing movements and skeletal muscle contractions (Figure 20-7) Breathing movements and skeletal muscle contractions (Figure 20-7) establish a fluid pressure gradient, as they do with venous bloodestablish a fluid pressure gradient, as they do with venous blood

Other factors, such as IF pressure, also drive lymphokinesis (Figure 20-8)Other factors, such as IF pressure, also drive lymphokinesis (Figure 20-8)

Lymphokinetic actions—activities that result in a central flow of lymphLymphokinetic actions—activities that result in a central flow of lymph

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Lymph Nodes Lymph Nodes

• Structure of lymph nodesStructure of lymph nodes

Lymph nodes are oval structures enclosed by a fibrous Lymph nodes are oval structures enclosed by a fibrous capsule (Figure 20-9)capsule (Figure 20-9)

Nodes are a type of biological filterNodes are a type of biological filter

Once lymph enters a node, it moves slowly through sinuses Once lymph enters a node, it moves slowly through sinuses to drain into the efferent exit vessel (Figure 20-10)to drain into the efferent exit vessel (Figure 20-10)

Trabeculae extend from the covering capsule toward the Trabeculae extend from the covering capsule toward the center of the nodecenter of the node

Cortical and medullary sinuses are lined with specialized Cortical and medullary sinuses are lined with specialized reticuloendothelial cells capable of phagocytosisreticuloendothelial cells capable of phagocytosis

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Lymph NodesLymph Nodes

• Locations of lymph nodesLocations of lymph nodes Most lymph nodes occur in groupsMost lymph nodes occur in groups

Location of groups with greatest clinical importance are Location of groups with greatest clinical importance are submental and submaxillary groups, and superficial submental and submaxillary groups, and superficial cervical, superficial cubital, axillary, iliac, and inguinal cervical, superficial cubital, axillary, iliac, and inguinal lymph nodes (Figures 20-11 through 20-13)lymph nodes (Figures 20-11 through 20-13)

Preauricular lymph nodes located in front of the ear Preauricular lymph nodes located in front of the ear drain superficial tissues and skin on the lateral side of drain superficial tissues and skin on the lateral side of the head and facethe head and face

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Lymph NodesLymph Nodes

• Functions of lymph nodes—perform two distinct functionsFunctions of lymph nodes—perform two distinct functions Defense functionsDefense functions

• FiltrationFiltration Mechanical filtration—physically stops particles from progressing further in the bodyMechanical filtration—physically stops particles from progressing further in the body

Biological filtration—biological activity of cells destroys and removes particles Biological filtration—biological activity of cells destroys and removes particles

• Phagocytosis—reticuloendothelial cells remove microorganisms and Phagocytosis—reticuloendothelial cells remove microorganisms and other injurious particles from lymph and phagocytose them (biological other injurious particles from lymph and phagocytose them (biological filtration)filtration)

• If overwhelmed, lymph nodes can become infected or damaged If overwhelmed, lymph nodes can become infected or damaged (Figures 20-14 and 20-15)(Figures 20-14 and 20-15)

Hematopoiesis—lymphoid tissue is site for final stages of Hematopoiesis—lymphoid tissue is site for final stages of maturation of some lymphocytes and monocytesmaturation of some lymphocytes and monocytes

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Lymphatic Drainage of the Breast Lymphatic Drainage of the Breast

• Clinically important because cancer cells and infections can Clinically important because cancer cells and infections can spread along lymphatic pathways to lymph nodes and other spread along lymphatic pathways to lymph nodes and other organs of the bodyorgans 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 vesselsDrained by two sets of lymphatic vessels

• Lymphatics that drain skin over breast with the exception of areola and nippleLymphatics 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 nippleLymphatics that drain substance of breast, as well as skin of areola and nipple

Superficial vessels converge to form a diffuse, cutaneous Superficial vessels converge to form a diffuse, cutaneous lymphatic plexuslymphatic plexus

Subareolar plexus—located under areola surrounding nipple; Subareolar plexus—located under areola surrounding nipple; where communication between cutaneous plexus and large where communication between cutaneous plexus and large lymphatics that drain the secretory tissue and ducts of the lymphatics that drain the secretory tissue and ducts of the breast occursbreast occurs

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Lymphatic Drainage of the BreastLymphatic Drainage of the Breast

• Lymph nodes associated with the breastLymph nodes associated with the breast

More than 85% of lymph from the breast enters More than 85% of lymph from the breast enters lymph nodes of axillary regionlymph nodes of axillary region

Remainder of lymph enters lymph nodes along Remainder of lymph enters lymph nodes along lateral edges of sternumlateral edges of sternum

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TonsilsTonsils

• Form a broken ring under the mucous membranes in the Form a broken ring under the mucous membranes in the mouth and back of the throat—the pharyngeal lymphoid mouth and back of the throat—the pharyngeal lymphoid ring (Figure 20-17)ring (Figure 20-17)

Palatine tonsils—located on each side of throatPalatine tonsils—located on each side of throat

Pharyngeal tonsils—located near posterior opening of nasal cavityPharyngeal tonsils—located near posterior opening of nasal cavity

Lingual tonsils—located near base of the tongueLingual tonsils—located near base of the tongue

• Protect against bacteria that may invade tissues around Protect against bacteria that may invade tissues around the openings between the nasal and oral cavitiesthe openings between the nasal and oral cavities

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ThymusThymus

• Location and appearance of the thymus Location and appearance of the thymus (Figure 20-18)(Figure 20-18)

Primary central organ of lymphatic systemPrimary central organ of lymphatic system

Single, unpaired organ located in the mediastinum, Single, unpaired organ located in the mediastinum, extending upward to lower edge of thyroid and extending upward to lower edge of thyroid and inferiorly as far as fourth costal cartilageinferiorly as far as fourth costal cartilage

Thymus is pinkish gray in childhood; with advancing Thymus is pinkish gray in childhood; with advancing age, becomes yellowish as lymphoid tissue is age, becomes yellowish as lymphoid tissue is replaced by fatreplaced by fat

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ThymusThymus

• Structure of the thymusStructure of the thymus

Pyramid-shaped lobes are subdivided into small Pyramid-shaped lobes are subdivided into small lobuleslobules

Each lobule is composed of a dense cellular Each lobule is composed of a dense cellular cortex and an inner, less dense, medullacortex and an inner, less dense, medulla

Medullary tissue can be identified by presence Medullary tissue can be identified by presence of thymic corpusclesof thymic corpuscles

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ThymusThymus

• Function of the thymusFunction of the thymus

Plays vital role in immunity mechanismPlays vital role in immunity mechanism

Source of lymphocytes before birthSource of lymphocytes before birth

Shortly after birth, thymus secretes thymosin and Shortly after birth, thymus secretes thymosin and other regulators, which enables lymphocytes to other regulators, which enables lymphocytes to develop into T cells (Figure 20-19)develop into T cells (Figure 20-19)

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SpleenSpleen

• Location of the spleen—in left hypochondrium, directly Location of the spleen—in left hypochondrium, directly below diaphragm, above left kidney and descending below diaphragm, above left kidney and descending colon, and behind fundus of stomach colon, and behind fundus of stomach (Figures 20-2 and 20-20)(Figures 20-2 and 20-20)

• Structure of spleen (Figure 20-21)Structure of spleen (Figure 20-21) Ovoid in shapeOvoid in shape

Surrounded by fibrous capsule with inward extensions that divide Surrounded by fibrous capsule with inward extensions that divide the organ into compartmentsthe organ into compartments

White pulp—dense masses of developing lymphocytesWhite pulp—dense masses of developing lymphocytes

Red pulp—near outer regions, made up of a network of fine Red pulp—near outer regions, made up of a network of fine reticular fibers submerged in blood that comes from nearby reticular fibers submerged in blood that comes from nearby arteriolesarterioles

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SpleenSpleen

• Functions of the spleenFunctions of the spleen Defense—macrophages lining sinusoids of spleen remove Defense—macrophages lining sinusoids of spleen remove

microorganisms from blood and phagocytose themmicroorganisms from blood and phagocytose them

Hematopoiesis—monocytes and lymphocytes complete Hematopoiesis—monocytes and lymphocytes complete their development in the spleentheir development in the spleen

Red blood cell and platelet destruction—macrophages Red blood cell and platelet destruction—macrophages remove worn-out RBCs and imperfect platelets and destroy remove worn-out RBCs and imperfect platelets and destroy them by phagocytosis; also salvage iron and globin from them by phagocytosis; also salvage iron and globin from destroyed RBCsdestroyed RBCs

Blood reservoir—pulp of spleen and its sinuses store bloodBlood reservoir—pulp of spleen and its sinuses store blood

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Cycle of Life: Lymphatic SystemCycle of Life: Lymphatic System

• Dramatic changes throughout lifeDramatic changes throughout life

• Organs with lymphocytes appear before birth and grow Organs with lymphocytes appear before birth and grow until pubertyuntil puberty

• PostpubertyPostpuberty Organs atrophy through late adulthoodOrgans atrophy through late adulthood

• Shrink in sizeShrink in size

• Become fatty or fibrousBecome fatty or fibrous

Spleen—develops early, remains intactSpleen—develops early, remains intact

• Overall function maintained until late adulthoodOverall function maintained until late adulthood Later adulthoodLater adulthood

• Deficiency permits risk of infection and cancerDeficiency permits risk of infection and cancer

• Hypersensitivity—likelihood of autoimmune conditionsHypersensitivity—likelihood of autoimmune conditions

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The Big Picture: The Lymphatic The Big Picture: The Lymphatic System and the Whole BodySystem and the Whole Body

• Lymphatic system drains away excess water Lymphatic system drains away excess water from large areasfrom large areas

• Lymph is conducted through lymphatic Lymph is conducted through lymphatic vessels to nodes, where contaminants are vessels to nodes, where contaminants are removedremoved

• Lymphatic system benefits the whole body Lymphatic system benefits the whole body by maintaining fluid balance and promoting by maintaining fluid balance and promoting freedom from diseasefreedom from disease