lymphatic system slides by barbara heard and w. rose. figures from marieb & hoehn 9 th ed....
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Lymphatic System
Slides by Barbara Heard and W. Rose.figures from Marieb & Hoehn 9th ed.
Portions copyright Pearson Education
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FunctionsLymphatic System
Solves a plumbing problem: leaky pipesReturns fluids that leaked from blood vessels (capillaries) back to blood
Solves a security problemMonitors for presence of foreign material and initiates defensive countermeasures when necessary
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FunctionsLymphatic System Components1.Lymphatic vessels (lymphatics)2.Lymphoid organs and tissues
Monitor lymph and initiate immune response if pathogens or abnormal cells are detected; provide a home for immune cells
3.Lymph – fluid in vessels
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Dept. of K.A.A.P.
Lymphatic Vessels (lymphatics)• Return interstitial fluid and leaked plasma
proteins back to blood• Approximately 3L / day• Once interstitial fluid enters lymphatics, it is
called lymph
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Lymphatic Vessels One-way system; lymph flows toward heartLymph vessels (lymphatics) include:
• Lymphatic capillaries• Collecting lymphatic vessels• Lymphatic trunks and ducts
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Dept. of K.A.A.P.
Marieb & Hoehn 9th ed. Fig 20.01a
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Lymphatic Capillaries
• Similar to blood capillaries, except– Very permeable (take up proteins, cell debris,
pathogens, and cancer cells)• Endothelial cells overlap loosely to form one-way minivalves
• Anchored by collagen filaments, preventing collapse of capillaries; increased ECF volume opens minivalves
– Pathogens travel throughout body via lymphatics
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Lymphatic Capillaries
• Absent from bones, teeth, bone marrow, and CNS
• Lacteals: specialized lymph capillaries present in intestinal mucosa– Absorb digested fat and deliver fatty lymph
(chyle) to the blood
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Figure 20.1b Distribution and special features of lymphatic capillaries.
Filaments anchoredto connective tissue
Endothelial cell
Flaplike minivalve
Fibroblast in looseconnective tissue
Lymphatic capillaries are blind-ended tubes in whichadjacent endothelial cells overlap each other, forming flaplike minivalves.
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Lymphatic Collecting Vessels
• Similar to veins, except– Have thinner walls, with more internal valves– Anastomose more frequently
• Collecting vessels in skin travel with superficial veins
• Deep vessels travel with arteries
• Nutrients supplied from branching vasa vasorum
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Lymphatic Trunks
• Formed by union of largest collecting ducts– Paired lumbar– Paired bronchomediastinal– Paired subclavian– Paired jugular trunks– Single intestinal trunk
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Lymphatic Ducts
• Lymph delivered into one of two large ducts– Right lymphatic duct drains right upper arm
and right side of head and thorax– Thoracic duct arises as cisterna chyli;
drains rest of body
• Each empties lymph into venous circulation at junction of internal jugular and subclavian veins on its own side of body
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Internaljugular vein
Entrance ofright lymphaticduct into vein
Entrance of thoracic ductinto veinThoracicduct
Cisternachyli
Collectinglymphaticvessels
Regionallymph nodes:
Cervicalnodes
Axillarynodes
Inguinalnodes
Aorta
Drained by the right lymphatic ductDrained by the thoracic duct
Lymphatic vessels and ducts
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Right jugular trunkRight lymphaticductRight subclaviantrunk
Right subclavianveinRight broncho-mediastinal trunk
BrachiocephalicveinsSuperiorvena cavaAzygos vein
Cisterna chyli
Right lumbartrunk
Lymphatic VesselsAnterior view of thoracic and abdominal wall.
Internaljugular veins Esophagus
TracheaLeft jugulartrunkLeft subclaviantrunk
Left subclavianveinEntrance ofthoracic ductinto veinLeft broncho-mediastinaltrunk
Ribs
Thoracic duct
Hemiazygosvein
Left lumbartrunk
Inferior vena cava
Intestinal trunk
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Lymph Transport
• Lymph propelled by– Milking action of skeletal muscle– Pressure changes in thorax during breathing– Valves to prevent backflow– Pulsations of nearby arteries– Contractions of smooth muscle in walls of
lymphatics
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Dept. of K.A.A.P.
Lymphoid Organs and TissuesStructural basis of immune systemHouse phagocytic cells and lymphocytesStructures•Lymph nodes•Spleen•Thymus•“MALT”: mucosa-associated lymphoid tissue
Tonsils, Peyer’s patches, appendix
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Lymphoid Cells
• Lymphocytes main warriors of immune system– Arise in red bone marrow
• Mature into one of two main varieties– T cells (T lymphocytes)– B cells (B lymphocytes)
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Lymphocytes
• T cells and B cells protect against antigens– Anything body perceives as foreign
• Bacteria and bacterial toxins, viruses, mismatched RBCs, cancer cells
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Lymphocytes
• T cells – Manage immune response– Attack and destroy infected cells
• B cells – Produce plasma cells, which secrete
antibodies• Antibodies mark antigens for destruction by
phagocytosis or other means
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Other Lymphoid Cells
• Macrophages phagocytize foreign substances; help activate T cells
• Dendritic cells capture antigens and deliver them to lymph nodes; activate T cells
• Reticular cells produce reticular fiber stroma that supports other cells in lymphoid organs
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Figure 20.3 Reticular connective tissue in a human lymph node.
Macrophage
Reticular cells onreticular fibers
Lymphocytes
Medullary sinus
Reticular fiber
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Lymphoid TissueHome and proliferation site for lymphocytesSurveillance vantage point for lymphocytes and macrophages Largely reticular connective tissueTwo main types
• Diffuse lymphoid tissue• Lymphoid follicles
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Diffuse Lymphoid Tissue•Lymphoid cells and reticular fibers in almost all body organs•Larger collections are found in lamina propria of mucous membranes: MALT
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Lymphoid Follicles(Nodules) Solid, spherical bodies of tightly packed lymphoid cells and reticular fibers
–Germinal centers of proliferating B cells–May form part of larger lymphoid
organs–Isolated aggregations of Peyer's
patches and in appendix
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Lymphoid Organs Tonsils (in pharyngeal
region)
Thymus (in thorax; most active during youth)
Spleen (curves around left side of stomach)
Peyer’s patches (aggregated lymphoidnodules in smallintestine)
Appendix
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Lymph Nodes
• Principal lymphoid organs of body
• Embedded in connective tissue, in clusters along lymphatic vessels
• Near body surface in inguinal, axillary, and cervical regions of body
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Internaljugular vein
Entrance ofright lymphaticduct into vein
Entrance of thoracic ductinto veinThoracicduct
Cisternachyli
Collectinglymphaticvessels
Regionallymph nodes:
Cervicalnodes
Axillarynodes
Inguinalnodes
Aorta
Drained by the right lymphatic ductDrained by the thoracic duct
Lymph node distribution
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Lymph Nodes
• Functions1. Filter lymph—macrophages destroy
microorganisms and debris
2. Immune system activation—lymphocytes activated and mount attack against antigens
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Structure of a Lymph Node
• Vary in shape and size but most bean shaped
• External fibrous capsule
• Trabeculae extend inward and divide node into compartments
• Two histologically distinct regions– Cortex– Medulla
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Structure of a Lymph Node
• Cortex contains follicles with germinal centers, heavy with dividing B cells
• Dendritic cells nearly encapsulate follicles
• Deep cortex houses T cells in transit
• T cells circulate continuously among blood, lymph nodes, and lymph
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Figure 20.4a Lymph node.
Afferentlymphaticvessels
Cortex• Lymphoid follicle• Germinal center• Subcapsular sinus
Efferentlymphaticvessels
Trabeculae
• Medullary sinus
• Medullary cord
MedullaHilum
Longitudinal view of the internal structure of a lymphnode and associated lymphatics
Capsule
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Structure of a Lymph Node
• Medullary cords extend inward from cortex and contain B cells, T cells, and plasma cells
• Lymph sinuses contain macrophages
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Figure 20.4b Lymph node.
Follicles
Trabecula
Subcapsularsinus
Capsule
Medullarycords
Medullarysinuses
Photomicrograph of part of a lymphnode (72x)
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Circulation in the Lymph Nodes
• Lymph– Enters convex side via afferent lymphatic
vessels; travels through large subcapsular sinus and smaller sinuses to medullary sinuses; exits concave side at hilum via efferent vessels
• Fewer efferent vessels so flow somewhat stagnate; allows lymphocytes and macrophages time to function
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Figure 20.4 Lymph node.
Afferentlymphaticvessels
Cortex
• Lymphoid follicle
• Germinal center
• Subcapsular sinus
Efferentlymphaticvessels Follicles
Trabecula
Subcapsularsinus
Capsule
Medullarycords
Medullarysinuses
Trabeculae
• Medullary sinus
• Medullary cord
Medulla
Hilum
Longitudinal view of the internal structure of a lymphnode and associated lymphatics
Photomicrograph of part of a lymphnode (72x)
Capsule
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KAAP
The procedure involves the injection of a dye (sometimes mildly radioactive) to pinpoint the lymph node which is closest to the cancer site. Sentinel node biopsy is used to stage many kinds of cancer, including lung and skin (melanoma). NYT ©2009.
Sentinel node biopsy is a technique which helps determine if a cancer has spread (metastasized), or is contained locally. When a cancer has been detected, often the next step is to find the lymph node closest to the tumor site and retrieve it for analysis. The concept of the "sentinel" node, or the first node to drain the area of the cancer, allows a more accurate staging of the cancer, and leaves unaffected nodes behind to continue the important job of draining fluids. NYT ©2009.
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Spleen
• Largest lymphoid organ
• Served by splenic artery and vein, which enter and exit at the hilum
• Functions– Site of lymphocyte proliferation and immune
surveillance and response– Cleanses blood of aged cells and platelets,
macrophages remove debris
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Figure 20.6c The spleen.
Diaphragm
Spleen
Adrenalgland
Leftkidney
Splenicartery
Pancreas
Photograph of the spleen in its normal position inthe abdominal cavity, anterior view.
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Spleen: Additional Functions
• Stores breakdown products of RBCs (e.g., iron) for later reuse
• Stores blood platelets and monocytes
• May be site of fetal erythrocyte production (normally ceases before birth)
• Encased by fibrous capsule; has trabeculae
• Contains lymphocytes, macrophages, and huge numbers of erythrocytes
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Structure of the Spleen
• Two distinct areas– White pulp around central arteries
• Mostly lymphocytes on reticular fibers; involved in immune functions
– Red pulp in venous sinuses and splenic cords
• Rich in RBCs and macrophages for disposal of worn-out RBCs and bloodborne pathogens
• Composed of splenic cords and sinusoids
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Figure 20.6a–b The spleen.
Splenicartery
Splenicvein Hilum
Diagram of the spleen,anterior view
Capsule
Trabecula
Splenic cordsSplenicsinusoidsArteriolesandcapillaries
Red pulp
White pulp
Central artery
Splenic artery
Splenic vein
Diagram of spleen histology
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Thymus
• Important functions early in life
• Found in inferior neck; extends into mediastinum; partially overlies heart
• Increases in size and most active during childhood
• Stops growing during adolescence, then gradually atrophies– Still produces immunocompetent cells, though
slowly
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Thymus
• Thymic lobules contain outer cortex and inner medulla
• Most thymic cells are lymphocytes– Cortex contains rapidly dividing lymphocytes
and scattered macrophages
• Medulla contains fewer lymphocytes and thymic corpuscles involved in regulatory T cell development (prevent autoimmunity)
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Capsule
Cortex
Medulla
Thymiccorpuscles
Figure 20.7 The thymus.
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Thymus
• Differs from other lymphoid organs in important ways– Has no follicles because it lacks B cells– Does not directly fight antigens
• Functions strictly in T lymphocyte maturation– Keeps isolated via blood thymus barrier
• Stroma of epithelial cells (not reticular fibers)– Provide environment in which T lymphocytes
become immunocompetent
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Mucosa-associated Lymphoid Tissue (MALT)
• Lymphoid tissues in mucous membranes throughout body
• Protects from pathogens trying to enter body
• Largest collections of MALT in tonsils, Peyer's patches, appendix
• Also in mucosa of respiratory and genitourinary organs; rest of digestive tract
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Tonsils
• Simplest lymphoid organs• Form ring of lymphatic tissue around pharynx
– Palatine tonsils—at posterior end of oral cavity– Lingual tonsil—grouped at base of tongue– Pharyngeal tonsil—in posterior wall of nasopharynx– Tubal tonsils—surrounding openings of auditory
tubes into pharynx
• Gather and remove pathogens in food or air
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Tonsils
• Contain follicles with germinal centers
• Are not fully encapsulated
• Overlying epithelium invaginates forming tonsillar crypts– Trap and destroy bacteria and particulate
matter – Allow immune cells to build memory for
pathogens
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Figure 20.8 Histology of the palatine tonsil.
Pharyngeal tonsil
Palatine tonsilLingual tonsil
Germinal centersin lymphoid follicles
Tonsillarcrypt
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Aggregates of Lymphoid Follicles
• Peyer's patches and appendix– Clusters of lymphoid follicles– In wall of distal portion of small intestine– Similar structures are also found in the
appendix– Destroy bacteria, preventing them from
breaching intestinal wall– Generate "memory" lymphocytes
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Figure 20.9 Peyer’s patch (aggregated lymphoid nodules).
Follicles of aPeyer’s patch(aggregatedlymphoid nodules)
Smooth muscle inthe intestinal wall
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College or Department name here
Spleen imagesSplenic cyst: http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJM200311273492222
Pelvic spleen: http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJMicm0802024
Impaled rower: http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJMcpc079004
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Dept. of K.A.A.P.
Figure 1. Computed Tomography of the Abdomen.
Coronal (Panel A) and axial (Panel B) images show splenomegaly (30 cm in greatest length, Panel A) and scattered, slightly enlarged lymph nodes in the para-aortic and splenic hilar regions (arrows, Panel B).
Abramson, Chatterji, Rahemtullah. “Case 39-2008 — A 51-Year-Old Woman with Splenomegaly and Anemia”. N Engl J Med 2008; 359:2707-2718
Dx: Splenic marginal-zone lymphoma (a lymphoma of B cells)Tx: Splenectomy, followed 15 mos later by chemotherapy when cancer symptoms returned.
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College or Department name here
Abramson, Chatterji, Rahemtullah. “Case 39-2008 — A 51-Year-Old Woman with Splenomegaly and Anemia”. N Engl J Med 2008; 359:2707-2718