The Lymphatic Sys (pgs 772-783)

 

v     Lymphatic Sys

Ø      2 purposes         

§        Carry lymph (draining body tissues- excess fluid from blood capillaries that went into interstitial space)

§        Immune sys (2 functions)

·       Gives lymphocytes a home

·       Sends lymph past WBC

 

v     Blood capillary    

Ø      Open at both ends

 

v     Lymph capillary (see diag. 20.1 pg 773)

Ø      One end open, one dead end

§        One way trap door

Ø      Very permeable

§        More fluid

Ø      3L/day into lymphatic sys: called “lymph” (clear H2O)

§        Stuff that can get out of blood capillary ] except blood proteins (ex albumin)

 

v     Differences between Blood & Lymph Capillaries

Ø      Blood

§        Open @ both ends

§        Permeable

§        Go everywhere

Ø      Lymph

§        Closed @ 1 end

§        VERY, VERY PERMEABLE

§        Not in bone, teeth or CNS

 

v     Lymph & Lymph Cap.

Ø      Very permeable

§        Anything can get in, but can’t go into blood capillaries

Ø      Valves

§        Act as trap doors

Ø      No tight/gap junctions

 

 

v     Lymphatic Sys

Ø      Lots of WBCs patrolling what goes by

Ø      Monocytes & macrophages

 

v     Infection

Ø      Lymph nodes swell

9     permanent home of B cells

·       T cells " thymus, travels

§        Cancer cells & pathogens

·       Handled by Immune sys & lymph nodes

 

v     Lacteals

Ø      Specialized lymphatic cap.

Ø      Intestines

Ø      Chyle

§        Fatty lymph

§        Not clear: milky, creamy

 

v     Differences between lymphatic & blood vessels

Ø      Lymphatic

§        Thinner walls

§        More anastomoses

§        More valves

 

v     Lymph Vessels

Ø      3 layers (same as b.v.)

 

v     Flow of Lymph

Ø      Capillaries

Ø      Vessels (collecting)

§        Same tunics as veins

§        Thinner walls

§        More valves & anastomoses

Ø      Trunks

§        Drain large portions of body

§        More, smaller

·       Paired

¨      Lumbar

¨      Bronchomediastinal

¨      Subclavian

¨      Jugular

·       Single

¨      Intestinal

Ø      Ducts

§        Thoracic duct

·       Drains most of body

·       Empties into internal jugular vein & subclavian vein

§        R. Lymphatic duct

·       Drains R. arm, R. head & thorax

 

v     Lymph Transport

Ø      Lower pressure than b.v.

Ø      No pump (ex. like heart)

§        Musc. Pump

§        Respiratory pump

§        Valves – prevent backflow

§        Pulsation of nearby arteries

§        Smooth musc peristalsis (rhythmically)

·       Trunks & ducts

Ø      Flow is still sporadic & slow

 

v     Bad infection

Ø      Rest = immobilization

§        Hinders flow of inflammatory material throughout body

 

v     Lymphoid Cells (see Immune Handout)

Ø      Lymphocytes

§        T cells (Cytotoxic and Helper)

·       Manage immune response

·       Attack invading cells

·       Becomes immunocompetent in Thymus

§        B cells

·       Make plasma cells (antibodies) & memory cells

·       Becomes immunocompetent in bone marrow

Ø      Macrophages & Dendritic Cells

§        Eat foreign cells

§        Help activate T cells

Ø      Reticular cell

§        Produce stroma (network made of fiber that supports other cell types in lymphoid organs)

§        Provide structure

 

v     Lymphoid Tissue

Ø      2 purposes

§        Where lymphocytes live and reproduce

§        Surveillance mechanism for lymphocytes & macrophages

Ø      Reticular CT

§        Macrophages – on fibers

§        Lymphocytes – spaces of network

·       Travel in circuit from lymph. tissues → blood → loose CT

Ø      Diffuse lymphatic tissue

§        No capsule

§        Scattered

§        Found in all organs

§        Most common in mucous membranes

Ø      Lymphoid follicles (nodules)

§        No capsule

§        Tightly packed

§        Germinal centers

·       Light staining

·       Dendritic & B cells

§        Found forming lymph nodes, as Peyer’s patches in intestine & in appendix

Ø      Lymph Nodes

§        In CT

§        2 functions

·       Filter lymph

¨      Macrophages – debris from CT & prevent it from entering blood & spreading to other parts of body

·       Help activate immune sys

¨      Lymphocytes – monitor lymphatic stream for antigens & mount attack against them

§        Structure

·       Capsule – container of CT

·       Trabecula – strands of CT that extend inward and divide node into compartments

·       Cortex

¨      Outside

¨      Superficial part

Ø      Densely packed follicles

Ø      Germinal centers

§        B cells

¨      Deep part

Ø      T cells in transit

·       Medulla

¨      Medullary cords – thin inward extensions of cortical tissue (from cortex)

¨      Contains lymphocytes & plasma cells

·       Lymph (medullary) sinus

¨      Lymph capillaries spanned by crisscrossing reticular fibers

¨      Few cells (mostly macrophages)

¨      Lymph

§        Circulation w/in lymph node

·       Afferent

¨      Lymph Arrives at node

·       Efferent

¨      Lymph Exits/Egresses node

·       Subcapsular space

¨      Space below the capsule

·       Hilus

¨      Indented region on concave side of node where the efferent vessels protrude off node

 

v     Other Lymphoid Organs

Ø      All made up of reticular CT

Ø      Spleen

§        Largest lymphoid org

§        L. side of abdominal cavity, curls around anterior aspect of stomach

§        Lymphocyte reproduction & lots of macrophages

§        Hilus

·       One artery in (Splenic A.)

·       One vein out (Splenic V.)

§        Functions

·       Extracting old & defective RBCs

·       Store or release parts of old RBC

¨      Store iron in spleen

¨      Release bilirubin

·       Make RBC (fetus only)

·       Stores platelets

¨      Clotting

§        White pulp

·       Areas composed mostly of lymphocytes suspended on reticular fibers

·       Small amounts

·       Cluster around arteries

§        Red pulp

·       Remaining splenic tissue

·       Cleans out damaged/worn-out RBCs & pathogens in blood

Ø      Thymus

§        2 lobes

§        Located bottom of neck, top of thorax, & in front of heart

§        Secretes hormones

·       Thymosin

·       Thymopietin

§        Immunocompetency of T cells (stimulated by thymocytes)

§        Does not directly fight antigens

§        Blood thymus barrier

·       Keeps antigens in blood from coming in contact w/ T cells

¨      Prevents premature activation of immature T cells

Ø      T cell must recognize self b4 recognizing invaders

§        No B cells

§        No Reticular cells

Ø      Tonsils (diag. 22.3 pg 832)

§        Simplest lymph org

§        Around entrance to throat

§        Palatine tonsils (paired)

·       Either side of posterior end of oral cavity

·       Largest & most often infected

§        Lingual tonsils (paired)

·       Base of tongue

§        Pharyngeal tonsil (single)

·       Posterior wall of nasopharynx

§        Tubal tonsils

·       Opening of auditory tubes and pharynx

§        Remove pathogens from food and air

§        Follicles & germinal centers

·       Lots of B cells & plasma cells

§        Crypts

·       Invaginations of surface epithelium

·       Trap bacteria & particulate matter

¨      Invited into lymphoid tissue where destroyed

Ø      Early warning sign against infections (memory B cells)

 

v     Aggregates of Lymphoid Follicles

Ø      Peyer’s patches

§        Clusters of lymphoid follicles in sm. Intestine

§        Function similar to tonsil

§        Crypt

Ø      Appendix

§        Blind pouch that comes off beginning of lg. intestine

§        Contains lots of bacteria

§        Lots of lymphoid tissue

·       Lymphocytes

Ø      Functions of Peyer’s patches & Appendix

§        Destroy bacteria

§        Make Memory B cell lymphocytes

·       Provide long term immunity