Lymphatic System Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9 th ed. Portions...

Lymphatic System

Slides by Barbara Heard and W. Rose.figures from Marieb & Hoehn 9th ed.

Portions copyright Pearson Education

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

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

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

Lymphatic Vessels One-way system; lymph flows toward heartLymph vessels (lymphatics) include:

• Lymphatic capillaries• Collecting lymphatic vessels• Lymphatic trunks and ducts

Dept. of K.A.A.P.

Marieb & Hoehn 9th ed. Fig 20.01a

© 2013 Pearson Education, Inc.

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


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


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.


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


Lymphatic Trunks

• Formed by union of largest collecting ducts– Paired lumbar– Paired bronchomediastinal– Paired subclavian– Paired jugular trunks– Single intestinal trunk


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


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


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


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

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


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)


Lymphocytes

• T cells and B cells protect against antigens– Anything body perceives as foreign

• Bacteria and bacterial toxins, viruses, mismatched RBCs, cancer cells


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


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


Figure 20.3 Reticular connective tissue in a human lymph node.

Macrophage

Reticular cells onreticular fibers

Lymphocytes

Medullary sinus

Reticular fiber


Lymphoid TissueHome and proliferation site for lymphocytesSurveillance vantage point for lymphocytes and macrophages Largely reticular connective tissueTwo main types

• Diffuse lymphoid tissue• Lymphoid follicles


Diffuse Lymphoid Tissue•Lymphoid cells and reticular fibers in almost all body organs•Larger collections are found in lamina propria of mucous membranes: MALT


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


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


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


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


Lymph Nodes

• Functions1. Filter lymph—macrophages destroy

microorganisms and debris

2. Immune system activation—lymphocytes activated and mount attack against antigens


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



• 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


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



• Medullary cords extend inward from cortex and contain B cells, T cells, and plasma cells

• Lymph sinuses contain macrophages


Figure 20.4b Lymph node.

Follicles

Trabecula

Subcapsularsinus

Capsule

Medullarycords

Medullarysinuses

Photomicrograph of part of a lymphnode (72x)


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


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

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.


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


Figure 20.6c The spleen.

Diaphragm

Spleen

Adrenalgland

Leftkidney

Splenicartery

Pancreas

Photograph of the spleen in its normal position inthe abdominal cavity, anterior view.


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


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


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


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


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)


Capsule

Cortex

Medulla

Thymiccorpuscles

Figure 20.7 The thymus.


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


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


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


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


Figure 20.8 Histology of the palatine tonsil.

Pharyngeal tonsil

Palatine tonsilLingual tonsil

Germinal centersin lymphoid follicles

Tonsillarcrypt


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


Figure 20.9 Peyer’s patch (aggregated lymphoid nodules).

Follicles of aPeyer’s patch(aggregatedlymphoid nodules)

Smooth muscle inthe intestinal wall

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

http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJM200311273492222

http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJMicm0802024

http://www.nejm.org.proxy.nss.udel.edu/doi/full/10.1056/NEJMcpc079004

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.

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

Lymphatic System Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9 th ed. Portions...

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