Lymphatic System

• Consists of:

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Lymph

Lymphatic vessels

Lymphatic tissue

Lymphatic nodules

Lymph nodes

Tonsils

Spleen

thymus

Lymphatic System

• Lymphatic Vessels– Functioning in returning interstitial fluid to the

vascular system.

• Lymphoid Organs and Tissues– House phagocytes and lymphocytes

– Activate the immune response

Lymphatic Vessels

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Return ISF to the bloodstream

Return leaked plasma proteins to the blood

Fluid within them is called lymph

1-way system flowing toward the heart

1 way systemback towardsthe heart

Blood Lymphaticvessel

PLASMA

vessel

LYMPH

INTERSTITIAL FLUID

or

TISSUE FLUID

Extracellularspace

How does lymph differ from plasma?

Lymphatic Vessels

• 4 types:–

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Lymphatic capillaries

Lymphatic collecting vessels

Lymphatic trunks

Lymphatic ducts

Lymphatic Capillaries

• What do they do?

Lymphatic Capillaries

• Blind

• Lined byendothelium– Loose

– Overlapping

• Permeability

• Flow

Lymphatic Capillaries

• Found just abouteverywhere that bloodcapillaries are found.– Exceptions

Lymphatic Capillaries

• Lacteals

– Specialized lymphaticcapillaries found in thevilli of the small intestine.

– Absorb fats from thedigestive tract.

Lymphatic Capillaries

Lymphatic

Collecting Vessels

-Similar to veins (in terms of the 3 tunics)

-Lots of valves

-Both superficial and deep

-Pass thru lymph nodes

* What happens to the lymph there?

What feature of lymphatic vessels is visible here? What do theyprevent? Why are they necessary?

Lymphatic Trunks

• Receive lymph from lymphatic collectingvessels.

• Types:–––––

JugularSubclavianBronchomediastinalIntestinalLumbar

Lymphatic Ducts

• Receive lymph from lymphatic trunks.

• Right lymphatic duct– Receives lymph from the right jugular, right subclavian,

and right bronchomediastinal trunks

– Empties into the right internal jugular vein

• Thoracic duct– Receives lymph from the left jugular, left subclavian,

left bronchomediastinal, intestinal, and lumbar trunks

– Empties into the left internal jugular vein

Lymphatic Vessels

Lymphatic Trunks

Lymphatic Ducts

Bloodstream

Where’s pressure high andwhere’s pressure low?

What makes lymph flow?

Lymph Flow

• Lymph flow will be similar to…

• 3 main factors promote lymph flow:– Skeletal muscle pump

– Respiratory pump

– Lymphatic smooth muscle

1. How does elevating an injured limb affectlymph flow?

2. How would exercise affect lymph flow?

3. How could massage affect lymph flow?

4. In some surgeries for breast cancer, thelymph nodes along thearm are removed inorder to assess the spread of the disease.What would be a result of this?

What happens when lymph cannot flow?

What could prevent lymph from flowing?

Filaria

• Lymphocytes– T lymphocytes

• Kill virus-infected and cancerous cells• Coordinate/control immune response

– B lymphocytes• Become plasma cells which secrete antibodies

• Phagocytes– Eat and kill and activate the rest of the immune system

• Dendritic cells– Activate the immune system

• Reticular cells– Make reticular fibers that support lymphatic tissues and

organs

Lymphoid Cells

Reticularconnectivetissue forms theframework ofmost lymphoidtissues andorgans.

Lymphoid Tissue

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Aggregations of lymphoid cells

Storage/proliferation site for lymphoid cells

Surveillance site

2 main types– Diffuse lymphatic tissue

– Lymphoid follicles

Diffuse Lymphatic Tissue

• What does “diffuse” mean?

• Found in lymph nodes and spleen.

• Especially prominent in the mucousmembranes lining the digestive, respiratory,urinary, and reproductive tracts.– Hence the term MALT.

Mucosa Associated Lymphatic Tissue

• Where are themucosae?

• Why is lymphoidtissue needed there?

• 2 main types:– GALT

– BALT

Lymphoid Follicles

• A.k.a. lymphoid nodules• Solid, packed spherical clusters of lymphoid

cells and reticular tissues• Often found as parts of larger lymphoid

organs (e.g., lymph nodes)• Found in the mucosae• Large number in the distal ileum and

appendix

Lymphoid follicle in thestomach

• Peyer’s Patches– Aggregates of lymphoid

follicles found in thedistal small intestine.

• Why there?

• Appendix– Blind outpocketing of the cecum.

– Contains aggregates of follicles.

Lymphoid Organs

• Surrounded by a capsule of denseconnective tissue.

• Lymph nodes

• Tonsils, thymus, spleen

Lymph Nodes

• Filter lymph

• Clustered alonglymphatic vessels

• Large superficial clustersin inguinal, axillary, andcervical regions.

Lymph Nodes

• Receive lymph from an afferent lymphatic vessel

• Drain lymph into an efferent lymphatic vessel

• Surrounded by dense CT capsule– Inward extensions (trabeculae) divide it into

compartments

• Reticular fibers support the resident macrophagesand lymphocytes

• Divided into a cortex and a medulla

Lymph Nodes

• Cortex contains:

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Subcapsular sinus

Cortical sinuses

Trabeculae

Diffuse lymphatic tissue

Lymphatic follicles

Lymph Nodes

• Medulla contains:– Medullary cords (diffuse lymphatic tissue)

– Medullary sinus

Flow Through the Node

Afferent lymphatic vessel

Subcapsular sinus

Cortical sinus

Medullary sinus

Efferent lymphatic vessel

What happens to the lymphduring this journey?

What does the lymph flowpast?

Spleen

• Largest lymphoid organ

• Sits just below the diaphragm,kind of behind the stomach andabove the kidney and colon.

• What protects it?

Spleen

• Major function is blood cleansing

– Removal of aged, broken, or malformed RBCs.• Who does this?

– Removal and destruction of pathogens and foreignmatter.

• Who does this?

Spleen

• Surrounded by a CT capsule w/ inward extendingtrabeculae

• Internal framework is provide by reticular fibers.

Spleen

• Splenic arterioles are surrounded by sheathesof lymphocytes.– This is known as the white pulp of the spleen.– What will happen here?

• The arterioles terminate in splenic capillaries –which are twisty, sinusoidal, and incomplete.– The capillaries and the surrounding splenic tissue

is referred to as the red pulp of the spleen.– Macrophages line the capillary surface.– Why?

Other Spleen Functions

• Storage of RBC breakdown products

• Platelet storage

• Fetal RBC production

Which wouldcontain moredamaged RBCsand morepathogens – thesplenic artery orthe splenic vein?

Thymus

• Largest and most activein fetus and infancy

• Involved in Tlymphocyte maturationand selection– Also, the removal of

those T cells that attackself tissue

• Growth ceases duringadolescence

• No direct fighting.

Tonsils

• Form a ring of lymphatic tissue at theentrance to the pharynx.

• 3 main types:– Palatine

– Pharyngeal

– Lingual

Palatine – located laterally in the posterior oral cavity.Largest and most often infected.

Pharyngeal – located in theposterior nasopharynx.A.k.a adenoids.

Lingual – located at thebase of the tongue.

Not fully encapsulated. Why not?

Contain crypts. What’s their advantage? What’stheir disadvantage?

Palatine Tonsil