Lymphatic System

Lympahtic System Role

Lympahtic system returns fluids leaked from blood vessels back into blood

3 Parts of lympahtic system

Network of lympahtic vessels

Lymph : fluid in vessels

Lymph nodes: cleanse lymph

Lymphoid organs and tissues

Prodivid structural basis of immune system by housing phagocytic cells and lymphocytes

Ex: spleen, thymus, tonsils, lymph nodes and other lymphoid tissues

Lymphatic vessels (lymphatics)

Elaborate network of drainage vesssles

Circulates about 3 liters of interstial fluid a day

Once interstitial fluid enters lymphatic it turns into lymph

What type of system are lympahtic vessels

They are one way system, lymph flows only towards heart

What do lymph vessels include

Larger lymphatic vessels

Lympahtic capillaries

What do lympahtic vessels return

Excess tissue fluid

Leaked proteins

Also carries absorbed fat to blood

Lympahtic capillary’s

Blind-ended vessels that weave between tissue cells and blood capillaries

Absent from bones teeth, bone marrow, and CNS (CNS uses CSF for drainage)

Similar to blood capillaries but more preamble

Can take larger molecules and particles that blood capillaries can’t

Ex: proteins,, cell debris, pathogens and cancer cells; acts as a route for pathogens or cancer cells to travel throughout body

Lympahtic Capillaires have increased permeability

This is due to two specialized structures

1. Endothelial cells overlap loosely to form one way minivalves

2. Structure of minivalves allow for responses to ECF changes

• increase in ECF volume opens minivalves more

• Decreases in ECF causes minivalves to close

Lacteals

Specialized lymph capillaries present in intestinal mucosa

They absorb digested fat and deliver fatty lymph (chyle) to blood

Larger lymphatic vessels

Lymph capillaries drain into increasingly larger vessels which are collecting lympahtic vessels

Larger lympahtic vessesl consist of

Collecting vessels, trunks and ducts

Larger lympahtic vessel structure

Similar to veins except they have thinner walls with more internal valves

Anastomose more frequently

Collecting vessels in skin travel with superficial veins, but deep vessels travel with arteries

Lympahtic trunks

Formed by union of largest collecting vessels, drain large areas of body

Named for regions of body they drain

Lymph delivered from trunks go into one of 2 larger lympahtic ducts

Each lympahtic duct empties lymph into venous circulation at junction of internal jugular and subclavian veins on its own side of body

Right Lympathci duct

Drains right upper arm and right side of head thorax

Thoracic Duct

Drain rest of body

Lymph system

Low pressure system like venous system

How is lymph propelled

By mailing 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

Physcial activity also increase flow of lymph:

-immobilization of area keeps needed inflammatory material in area for faster healing

What do lymphoid cells consist of

Immune system cells found in lymphoid tissue

Supporting cells that form lymphoid tissue structures

Immune system cells

Lymphocytes, macrophages, dendritic cells and reticular cells

Lymphocytes

Cells of the adaptive immune system; mature into one of two main types

T cells (t Lymphocytes)

B cells (B lymphocytes)

Main functions of lymphoid tissue

Houses and provides proliferation sites for lymphocytes

Offers survellience vantage points for lymphocytes and macrophages as they filter through lymph

What are lymphoid tissues composed of

Reticular connective tissue

Macrophages live on reticular fibers

Spaces between fibers offer a place for lymphocytes to occupy when they return from patrolling body

Two main types of lymphoid tissue

Diffuse lymphoid tissue and lymphoid follicles (nodules)

Diffuse lymphoid tissue

Loose arrangement of lymphoi cells and some reticular fibers

Found in nearly every bod organ

Larger collections in a layer of mucous membranes

Lymphoid follicles (nodules)

Solid, spherical bodies consisting of tightly packed lymphoid cells and reticular fibers Found

Consume germinal centers of proliferating B cells

May form part of larger lymphoid organs (nodes)

Isolated aggregations of Peter’s patches and in appendix

Primary Lymphoid organs

Areas where T and B cells mature

T and B cells originate in bone marrow

B cells mature in bone marrow; T cells mature in thymus

Secondary lymphoid organs

Areas where mature lymphocytes first encounter their antigen and become activated

Nodes spleen, MALT (mucosa associated lymphoid tissue) and diffuse lymphoid tissues

Lymph nodes

Principal secondary lymphoid organs of body

Hundreds of them are found throughout the body

Most are embedded deep in connective tissues in clusters along lymphatic vessels

Some are nearer to body surface in inguinal, axillary, and cervial regions of body where collecting vessels converge into trunks

Function of lymph nodes

Cleansing the lymph: act as lymph filters

• macrophages remove and destroy microorganisms and debris that enter lymph

• Prevent unwanted substances from being delivered to blood

Immune system activation: offer a place for lymphocytes to become activated and mount attacks against antigens

Structure of lymph nodes

Vary in shape and size but most are small and bean shaped

They are surrounded by fibrous capsule

Capsule fibers extend inward as trabeculae and divide node into compartments

Two distinct regions of lymph node:

1. Cortex: have germinal centers for B cells, houses T cells in transit, has dendritic cells

2. Medulla: has sinuses and both lymphocytes, macrophages

Buboes

Inflamed, swollen, tender lymph nodes that result when nodes are overwhelmed by what they are trying to destroy

• condition often referred to as swollen glands

• Bubobes sometimes pus filled

• Bubonic plague was named after chief clinical feature of this disease

Lymph nodes and cancer

Lymph nodes can become secondary cancer sites if metastasizing cancer cells become trapped in nodes

_ cancer infiltrated lymph nodes: swollen but usually not painful

Spleen

Blood rich organs about size of fist, located left side of abdominal cavity, below stomach

Largest of the lymphoid organs

Served by splenic artery and vein (enter and exit hilum)

Encased by fibrous capsule and also has trabeculae

Functions of spleen

site of lymphocyte proliferation and immune surveillance response

Cleanses blood of aged blood cells and platelets; macrophages and debris

Stores breakdown of RBC for later use

Stores blood platelets and monocytes for release into blood when needed

May be site of fetal erythrocyte production

2 histology components of spleen

Red pulp: site of RBC and pathogen destruction

White pulp: site of immune function

Spleen Thin Capsule

Direct blow or severe infection may cause it to rupture, spilling blood into peritoneal cavity

Splenectomy

Surgical removal of ruptured spleen

Once standard treatment to prevent hemorrhage and shock

Spleen can repair itself, so frequency of splenectomy has decreased

Mucosa associated lymphoid tissue (MALT)

Lymphoid tissue in mucous membranes throughout body

Protects from pathogens trying to enter body

Found in mucosa of respiratory tract, genitourinary organs, and digestive tract with the largest collection found

• tonsils

• Peter’s patches

• Appendix

Tonsils

Simplest lymphoid organ

Form ring of lymphatic tissue around pharynx, they appear as swellings of mucosa

Name according to location

Palatine tonsil

At posterior end of oral cavity

Largest of tonsils and most often infected

Lingual tonsils

Lumpy collection of follicles at base of tongue

Pharyngeal tonsil

AKA adenoids

Located in posterior wall of nasopharynx

Tubal tonsils

Surround openings of auditory tubes into pharynx

Tonsil functions

Gather and remove pathogens in food or air

Contain follicles with germinal centers and scattered lymphocytes

Not fully encapsulated

Overlying epithelium invaginates, creating crypts

Tonsil crypts

Bacteria or particulate matter enters crypts where they are trapped and destroyed

Risky to lure bacteria into tissues

Allows immune cells to become activated and build memory cells against these potential threats

Peyers patches

Clusters of lymphoid follicles in wall of distal portion of small intestine

Structurally similar to tonsils

Function of Peyers patches

Destroy bacteria, preventing them from breaching intestinal wall

Generate memory lymphocytes

Appendix

Offshoot of first part of large intestine

Contains large number of lymphoid follicles

Appendix function

Destroy bacteria, preventing them from breaching intestinal wall

Generate memory lymphocytes

Appendicitis

Inflammation of appendix

Symptoms:

• right abdominal pain

• Nausea

• O minting

• Deceased appetite

• 1/3 of people do not have these symptoms

Rupture can have widespread, painful inflammation of the abdominal wall and sepsis

Thymus

Biloped lymphoid organ found in inferior neck

Functions as lymphoid organ where T cells mature

• most active and largest in size during childhood

• Stops growing during adolescence, then gradually atrophies

• Still produces immunocompetent cells, though more slowly

Thymus Lobes

Outer cortex: contains rapidly dividing lymphocytes (the bulk of cells) and scattered macrophages

Medulla contains fewer lymphocytes and have thumic corpuscles

Thymic corpuscles

Where regulatory T cells develop

remember: T cells that help to prevent autoimmunity

Thymus Differs from other lymphoid organs in what ways

Has no follicles because it lacks B cells

Does not directly fight antigens

• functions strictly in T lymphocyte maturation

• Contains blood thymus barrier: keeps immature T lymphocytes isolated from any antigens; this prevents premature activation

• Stroma: made up of epithelial cells, not reticular fibers; provide environment in which T lymphocytes become immunocompoetent