The Lymphatic System
The lymphatic system is a drainage system, collecting and returning intestinal fluids.  As with the blood
network the lymph vessels form a network throughout the body, unlike the blood the lymph system is a
one-way street draining lymph from the tissue and returning it to the blood.  This system is a network of
capillaries and tubes called lympahtics.  These lymphatics drain lymph (Lymph is composed of water,
protein, salts, glucose, urea, lymphocytes and other substances.) from all over the body.  The lymphatic
system defends the body against disease by producing lymphocytes.  It also absorbs lipids (fats) from the
intestines and delivers them to the blood.

Lymphatics are found in every part of the body
except the central nervous system.  The main components
of the lymphatic system are
bone marrow, lymph nodes, spleen, and the thymus gland.

Lymphocytes develop in the thymus gland or in the bone marrow.  Lymphocytes are called white blood
cells.  Two types of
white blood cells are the T cells and B cells.  Lymphocytes in the lymph nodes aid the
body in fighting infection by producing antibodies that destroy bacteria and viruses.      

Lymph nodes are filters for lymph and may range in size from very tiny to 1 inch in diameter.  They can be
found in groups located in different areas of throughout the body, including the neck, armpit, chest,
abdomen, pelvis and groin.  Approximately two thirds of all lymph nodes and lymphatic tissue are within or
near the gastrointestinal tract.  Lymph nodes provide an environment where lymphocytes can gain
exposure to antigens (viruses, bacteria, fungi and etc.). This exposure causes the lymphocytes to perform
immune functions.

The major lymphatic vessel is the thoracic duct, which starts near the lower part of the spine.  It collects
lymph from the lower portion of the body.  It runs through the body and empties into the blood through the
large vein near the left side of the neck.  The right lymphatic duct collects lymph from the right side of the
neck, chest and arm, and empties into a large vein on the right side of the neck.  

The spleen is largest lymph organ and is a filter for blood.  The spleen helps to control the amount of
blood and blood cells that circulate through the body also aiding in destroying damaged cells.  The spleen
if found in the upper left region of the abdomen.  Although the spleen performs many important functions it
is not necessary to sustain life.

The thymus gland lies behind the sternum and expands upward into the root of the neck.  Lymphocytes
originate from (stem cells) in red bone marrow.  These enter the thymus gland to mature and develop into
activated T-lymphocytes able to respond to antigens encountered elsewhere in the body.  

The Lymphatic Process
There are three main types of lymphatic vessels; lymph capillaries, lymphatics and lymph ducts.

Lymph capillaries are microscopic tubes located between cells.  Lymph capillaries resembles blood
capillaries somewhat, but differ in important ways.  Whereas a blood capillary has an arterial and venous
end.  A lymph capillary has no arterial end.  Instead  each lymph capillary originates as a closed tube.  
Lymph capillaries also have a larger irregular lumen (inner space) than blood capillaries and are more
permeable (defused).   Lymph capillaries branch and interconnect freely and extend into almost all tissues
of the body except the Central Nervous System and the a vascular tissues such as the epidermis (outer
most layer of the skin) and the cartilage.  Lymph capillaries join to form vessels called lymphatics or lymph
veins.  These resemble blood-conducting veins but have thinner walls and relatively larger lumen, and
they have more valves.  In the skin, lymphatics are located in subcutaneous tissue and follow same paths
as veins. In the viscera (the internal organs of the body), lymphatics generally follow arteries and form
plexuses (networks) around them.

At certain locations lymphatics enter the lymph nodes.  These are structures that consists of lymphatic
tissue.  As the lymph flows slowly through the lymph sinuses within the tissue of the lymph node, it is
filtered.  Macrophages remove bacteria and other foreign matter as well as debris.  Lymphocytes are
added to the lymph as it flows through the sinuses of a lymph node.  Thus the lymph leaving the node is
both cleaner of debris and richer in lymphocytes.  Lymphatics leaving the lymph nodes called efferent
lymph vessels and conduct lymph toward the shoulder region.  Large lymphatics that drain groups of
lymph nodes are often called lymph trunks.

Lymphatics from the lower portion of the body converge to form a dilated lymph vessel,(the cisterna chyli)
in the lumbar region of the abdominal cavity.  The cisterna chyli (cistern - large tank or holding area)
extends for about 6 centimeters just to the right of the abdominal aorta.  At the level of the twelfth thoracic
vertebra, the cisterna chyli narrows and becomes the thoracic duct.  Lymphatic vessels from all over the
body, except the upper right quadrant, drain into the thoracic duct.  This vessel delivers the lymph into the
base of the left subclavian vein at the junction of the left subclavian and internal jugular veins.  In this way
lymph is continuously emptied into the blood where it mixes with the plasma.  At the junction of the thoracic
duct and the venous system, a valve prevents blood from flowing backward into the duct.

Only about 1 centimeter in length, the right lymphatic duct receives lymph from the lymphatic vessels in the
upper tight quadrant of the body.  The right lymphatic duct empties lymph into the base of the right
subclavian vein (at the point where it unites with the internal jugular vein to form the brachiocephalic).

source - jdaross.mcmail.com
Definitions

Lymph vessels
- Are channels or
ducts that contain and convey
lymph.

Lymph - A pale fluid that is
composed of water, protein, salts,
glucose, urea, lymphocytes and
other substances,

Lymph nodes - Are masses of
lymphoid tissues; they contain
lymphocytes.

Lymphocytes - Are white blood
cells.

Immunoblasts - Are lymphocytes
that become enlarged when they
encounter foreign substances.

Macrophages - Are white blood
cells that remove damaged cells
from the blood stream.

Antibodies - Chemicals produced
by white blood cells to fight
bacteria, viruses and other foreign
substances.

Thoracic Duct - A major lymphatic
vessel.  This vessel begins near
the lower part of the spine and
collects lymph from the lower
limbs, pelvis, abdomen, and lower
chest.  The lymph flowing through
the duct empties into a large vein
in the upper chest and returns to
the blood stream.

The Spleen - Is an organ found on
the left side of the abdomen.  The
spleen helps control the amount of
blood and blood cells that circulate
through the body and helps destroy
damaged cells.

The Thymus Gland - Stem cells
enter the thymus gland to  mature
and develop into activated
T-lymphocytes.
Little Leakers
The Lymphatic System
Example - Lymphadenopathy of the
neck might be a result of an
infection of the throat.

Lymphadenitis - An inflammation of
the node due to an infection of the
tissue in the node itself.   (Swelling,
tenderness, and sometimes redness
and warmth of the overlying skin)

Tonsillitis - The collections of
lymphoid tissue in the back of the
mouth at the top of the throat; that
are involved in a bacterial or viral
infection that causes them to
become swollen and inflamed.  

Splenomegaly (enlarged spleen) -
The spleen is generally small
enough that it can't be felt by
pressing on the abdomen.  The
spleen can enlarge to several times
it's normal size with certain diseases.
The most common is infection
(particularly viral infections).  
Children with an enlarged spleen
should avoid contact sports, they
could cause a life-threatening loss
of blood it their spleen was to
rupture.
The spleen also helps fight off infection.  The spleen contains antibody producing lymphocytes.  These lymphocytes weaken or kill bacteria,
viruses and other organisms.  And if the blood that passes through the spleen is carrying damaged cells the spleen will destroy them and
clear them from the blood stream.

The Importance of the Lymphatic System
The lymphatic system flows toward the bloodstream.  It returns fluid from the body tissues to the blood.  If the excess fluids had no way to
return to the blood the tissues would become swollen.  When a body part becomes swollen the lymph vessels collect the excess fluid and
carry it to the veins through the lymphatic system.

This process is detrimental because water, proteins, and other molecules continuously leak out of tiny blood capillaries into the
surrounding body tissues.  This lymph fluid has to be drained, so it then returns to the blood stream via the lymphatic vessels.  

Lymphatics and the absorption and transport of fats
Small quantities of very small fatty acids are able to directly enter the intestinal capillaries of the villi of the small intestine and hence enter
the blood stream in this way.  However, the majority of the fatty acids are
long chained and are absorbed quiet differently.  This happens  
within the intestinal lumen, bile salts from aggregates (called micelles that are water soluble).  Fatty acids and monoglycerides are
aggregated into the centers of the micelles.  The micellas transport the fatty acids and monoglycerides to the brush borders of the villi.  The
micelles continue their ferrying function in the intestinal lumen.  Within the epithelial cells, the fatty acids and monoglycerides are
resynthesised into triglycerides.  The triglycerides combine and cholesterol, lipoprotein, and phospholipids to form globules called
chylomicrons.  The chylomicrons leave the epithelial cells and enter into the lacteal of the villus.  Lymphatic vessels then carry the
chylomicrons to the venous blood of the left subclavian vein via the thoracic duct.  

The Importance of the Lymphatic System
The lymphatic system flows toward the bloodstream.  It returns fluid from the body tissues to the blood.  If the excess fluids had no way to
return to the blood the tissues would become swollen.  When a body part becomes swollen the lymph vessels collect the excess fluid and
carry it to the veins through the lymphatic system.

This process is detrimental because water, proteins, and other molecules continuously leak out of tiny blood capillaries into the
surrounding body tissues.  This lymph fluid has to be drained, so it then returns to the blood stream via the lymphatic vessels.

sources -
 lymphomation.org, gorhams.dk, bbc.co.uk, jdaross.mcmail.com, bodyteen.com -  with thanks
In a run down
The Lymph drains into open-ended one-way lymph capillaries.  Lymph moves slower than blood and is pushed along by the bodies
movements; such as breathing.  The walls of these capillaries are very thin with tiny openings; this allows gases, water and chemicals to
pass through and nourish the cells as well as to take away any waste.  Intestinal fluid passes out of these openings to bathe the body
tissues.  The lymph vessels recycle the intestinal fluid and return it to the blood stream into the circulatory system. The fluid is collected
from the body tissues and emptied into the large veins in the upper chest, near the neck.

Lymph nodes are made up of a mesh like network of tissue.  The lymph enters the lymph node and travels through passages called
sinuses.  The nodes contain macrophage's that destroy bacteria, dead tissue, and other foreign matter, removing them from the blood
stream.

If a person has an infection germs will collect in the lymph nodes, this will cause the nodes to swell.  If all of the germs can not be
destroyed a local infection in the nodes may result.