Biology 2402 A&P II   Lecture Notes 
Lymphatic     
Dr. Weis  

Lymphatic System consists of vessels and tissues/organs that

                        : have ties with the cardiovascular system and the immune system & GI

Lymphoid tissues/organs --> Collection of organs and tissues involved with

Lymphatic vessels (lymphatics) --> return fluid back to cardiovascular system

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I. Lymphatic Vessels :

1. drainage vessels that collect excess protein contained in interstitial fluid
( the fluid not reabsorbed at the venous end of the capillary) and returns it to the  venous system.

2. Once interstitial fluid enters the lymphatics it is called LYMPH.

3. One way system toward the heart......begins at the lymphatic capillaries, blind ended, terminal vessels.
Vessel permeability reflects the endothelial cells that overlap to form a flap or valve  instead of a tight junction.
When fluid in the interstitial spaces increases, anchoring fibers (connective tissue fibers) that are attached from the endothelial cells to the surrounding connective tissue will allow the cells to separate and create gaps in the vessel wall to allow fluid and large particles (proteins) to enter. This also means that cells, debris, pathogens, cancer cells, etc. can enter as well.

4. When the pressure increases on the inside of the lymphatics, the cell gaps are closed.

  *** specialized lymph capillaries in the intestinal mucosa called lacteals will drain the digestive track and also absorb fat.  This lymph fluid is called chyle and will appear  milky white and have a high protein content (3-4 gm/dl) as well as chylomicrons.

5. Lymphatic capillaries --> collecting vessels which can follow superficial veins (called superficial lymphatics) or follow deep veins (called deep lymphatics)--->lymphatic trunks that collect lymph from major regions ::

the lymph collected in the lymphatic trunks from these regions will then empty into 2 large, major DUCTS

6. Final ducts :

        b. Thoracic Duct...............drains lymph from

7. Each duct empties into the venous circulation at the junction of internal jugular and subclavian veins. 

To summarize ::

Right lymphatic duct ---> rt side  (rt internal jugular & right subclavian v.)

Thoracic duct  --> left side (left internal jugular & left subclavian v.)

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  Lymphatic vessels have a low pressure and therefore slow the transport of lymph, ~ 3 liters in 24 hours.

 Valves in the collecting lymphatics allow for one way flow. 

     Lymph return is determined by :

  Therefore lymphatic function will :

All these affect capillary dynamics in relation to the changes in the ISCF pressures

 (colloid osmotic fluid verses hydrostatic, now called hydraulic)

Lymphatics also maintain and distribute lymphocytes

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****Problems ::

blockage/obstruction to flow  and increasing ISCF pressure = EDEMA

   localized edema --> lymph edema (usually due to lymphatic removal during cancer surgery)

!!!!!!!!!!!!!!!!!! FYI :: there are NO lymphatics in the CNS

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Lymphoid Tissues and Organs

There are two sites for lymphocyte location::  Primary and Secondary

1. Primary sites are for maturation and release of lymphocytes and will include the yolk sac, fetal liver, bone marrow & thymus

2. Secondary sites are tissues seeded with lymphocytes and include Lymph nodes (glands), spleen, lymph nodules, and bone marrow.

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II. LYMPH NODES  (Lymph Glands)   Abbrev. ::  L.N.

fxn : filter lymph [no other lymphatic organ filters lymph since LN are the only ones with afferent lymphatics]

A. Regions of the Lymph Node ::

The basic foundation of a lymph node is the architecture of the reticular C.T. containing cells in various regions.

1. Cortex --> Lymphocytes packed in spherical follicles with germinal centers.

2. Medullary cords are formed by the extension of cortex lymphocytes (B cells) into the medulla.

3. Medulla :: M0 in medullary sinuses and along the fibers of the reticular network.

In a lymph node,  90% of lymphocytes are derived from the blood.  10% are derived from lymph.

The control rate for lymphocyte migration is due to an activation process.  Once activated, the lymphocytes will migrate to the affected tissue.

B. Circulation ::  one way through several Lymph Nodes

1. Afferent lymphatic vessels

Lymph delivered and enters into a subscapsular sinus and flow through the interconnected sinuses and exits at the hilus through efferent vessels.

2. Fewer efferent vessels at the hilus, so lymph is slowed as it goes through the node.

3.  Each node (gland) will drain certain areas of the body and are named for their region. 
Examples :: Cervical L.N., Axillary L.N., Inguinal L.N., Intestinal L.N.

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*****Problems :: chronic enlargement --> Lymphadenopathy due to disease, bacteria, virus,

cancer sites --> lymphoma, Hodgkins disease  circulation of cancer cells through lymphatics

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III. Other Lymphoid Organs :: spleen, thymus
Other Lymphoid Tissues:: tonsils, GALT (gut associated lymphatic tissue)

!!!!! DO NOT FILTER LYMPH because they are NOT associated with afferent lymphatics

tissue makeup --> reticular connective tissue for cell support

                 lymphocytes arranged in nodules or follicles, must have T and B cells to have proper structure

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A. Spleen ::

Largest lymphoid organ
beneath diaphragm (in abdomen) on the left side
Function:

Circulation : splenic artery/vein enters and leaves at hilus

Structure : thin fibrous connective tissue capsule forms trabeculae (inner branches)

cells form the PULP  ::

*** Problems :: rupture, can be removed ---> Splenectomy

  tumor --> hemangiosarcoma, hemangioma, lymphoma

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B. Thymus ::

Anterior mediastinum, deep to sternum, associated with the base of the heart

found in young, present until puberty, then atrophies

hormones (Tymosins) affect lymphocytes (T cells)

 Structure :: capsule divides gland into two lobes (Right ,Left)

Cortex :: Lymphocytes densely packed with reticular epithelial cells that help maintian the blood-thymus barrier.

Medulla :: epithelial cells forming thymic [Hassall's] corpuscle secrete a collection of hormones called Thymosins that aid in programming lymphocytes to become thymic [T] lymphocytes.

Gland atrophies after puberty, loss of cells, fat replaces

Problems :  athymic aplasia  (born without a thymus)

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C. Tonsils ::

lymphatic tissue in pharynx, named for location

structure -->

lymphocyte nodules/follicles with germinal centers

squamous epithelium is invaginated to form blind ended crypts to trap bacteria and expose organsisms to immune system

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D. GALT [also known as MALT = Mucosa Associated Lymphatic Tissue]

      (1) Peyer's Patches ::

lymph nodules tht contain lymphocytes & M0 in submucosal region of small intestine called the ileum. 

      (2)  Appendix :: vermiform appendage, lymphocytes predominate in submucosa

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IV. Development :: most all from mesoderm

   lymph nodes and vessels from budding of sacs from veins

   mesenchymal cells migrate to sites of reticular tissue

   Thymus from endoderm, and outgrowth of pharynx and is the first lymphoid organ to develop

Lymphocytes from bone marrow and thymus will infiltrate organ structures.

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**** Problems ::