LYMPHATIC SYSSTEM
PREPARED BY MR. ABHIJIT DAS
The lymphatic system is a network of vessels, nodes,
and organs that transport lymph throughout
the body.
COMPOSITION OF LYMPH
Lymph is a colorless fluid
that circulates through the lymphatic system, playing a crucial role in the
immune system. It is derived from interstitial fluid and it contains a variety
of components. The composition of lymph includes:
1.
Water:
The majority of lymph is water.
2.
Electrolytes:
Lymph contains various electrolytes, including ions such as sodium, potassium, calcium, and chloride. These
ions help maintain the osmotic balance and pH of the lymph.
3.
Proteins:
Lymph contains proteins that have leaked from the blood capillaries into the
interstitial fluid and are then transported by the lymphatic system. These
proteins include antibodies, enzymes, clotting
factors, and other plasma proteins.
4.
White Blood Cells (Lymphocytes):
Lymph is rich in white blood cells, particularly lymphocytes.
Lymphocytes are a crucial component of the immune system and are responsible
for recognizing and attacking foreign substances, such as bacteria, viruses,
and other pathogens.
FUNCTIONS
1.
Fluid Balance:
·
The lymphatic system helps maintain
fluid balance in the body by collecting excess fluid, known as lymph, that
leaks from blood vessels into the surrounding tissues. This fluid is then
transported back to the bloodstream, preventing the accumulation of excess
fluid in tissues and contributing to the regulation of blood volume.
2.
Immune System Support:
·
The lymphatic system is a crucial
component of the immune system. Lymph nodes, which are small, bean-shaped
structures, act as filters that trap and remove foreign substances, such as
bacteria and viruses, from the lymph. White blood cells within the lymphatic
system play a key role in recognizing and destroying pathogens, thereby helping
to defend the body against infections.
3.
Absorption of Dietary Fats:
·
In the small intestine, the lymphatic
system is involved in the absorption of dietary fats and fat-soluble vitamins.
Specialized lymphatic vessels called lacteals absorb these nutrients from the
digestive tract and transport them through the lymphatic system to the
bloodstream.
4.
Transport of White Blood Cells:
·
The lymphatic system serves as a channel
for the movement of white blood cells, including lymphocytes, which are crucial
components of the immune system. These cells travel through the lymphatic
vessels and lymph nodes, patrolling the body to detect and respond to
infections or abnormal cells.
PATHWAYS OF LYMPHATIC CIRCULATION
1.
Interstitial Fluid Formation:
·
Interstitial fluid is formed as a result
of fluid that leaks out of blood capillaries and bathes the body's tissues.
2.
Initial Lymphatic capillaries:
·
Microscopic vessels called initial
lymphatic capillaries collect the excess interstitial fluid, which is now
called lymph.
3.
Larger Lymphatic Capillaries:
·
Initial lymphatic vessels merge to form
larger lymphatic capillaries. These capillaries have one-way valves that allow lymph to enter but prevent it from
flowing backward.
4.
Lymphatic Vessels:
·
The lymphatic capillaries join together
to form larger lymphatic vessels, which resemble veins. These vessels continue
to transport lymph.
5.
Lymph Nodes:
·
Along the lymphatic vessels are
structures called lymph nodes. These nodes filter and
cleanse the lymph by removing debris, pathogens, and abnormal cells.
6.
Lymphatic Trunks:
·
The lymphatic vessels converge into
larger vessels called lymphatic trunks. There are several major trunks,
including the thoracic duct and the right lymphatic duct.
7.
Thoracic Duct or Right Lymphatic
Duct:
·
The thoracic duct collects
lymph from the lower body and the left side of the upper body, while the right lymphatic duct collects lymph from the right side of the upper body. These ducts then empty
lymph into the veins of the neck.
8.
Venous Circulation:
·
Finally, the cleansed lymph re-enters
the bloodstream through the subclavian veins,
completing the lymphatic circulation loop. From here, it mixes with the blood
and becomes part of the overall circulatory system.
LYMPHOID ORGANS
There are two types
of lymphoid organs such as primary lymphoid organs and
secondary lymphoid organs.
Primary lymphoid organs are those organs where
immune cells develop and mature. Secondary lymphoid organs are those organs
where mature immune cells respond to antigens and initiate immune responses.
1. PRIMARY
LYMPHOID ORGAN:
·
Bone Marrow:
This is a primary lymphoid organ where hematopoiesis occurs. Hematopoiesis is
the process of blood cell formation, including the production of lymphocytes (B
cells and T cells).
·
Thymus:
The thymus is another primary lymphoid organ. It is responsible for the
maturation and selection of T cells (a type of white blood cell).
2.
SECONDARY LYMPHOID ORGANS:
·
Lymph Nodes:
Lymph nodes are small, bean-shaped structures located throughout the lymphatic
system. They act as filters for the lymphatic fluid, trapping and removing
foreign particles, such as bacteria or viruses.
·
Spleen:
The spleen filters the blood and helps to remove damaged blood cells and
foreign substances. It contains white pulp, where immune responses can be
initiated.
·
Tonsils and Adenoids:
These are collections of lymphoid tissue located in the throat. They act as the body's first line of defense against
ingested or inhaled pathogens, helping to trap and eliminate them.
·
Peyer's Patches:
Found in the lining of the small intestine,
Peyer's patches are clusters of lymphoid tissue. They play a role in monitoring
the intestinal contents for potential pathogens and contribute to the immune
response in the gut.
·
Mucosa-Associated Lymphoid Tissue
(MALT): MALT includes various lymphoid tissues associated
with mucosal surfaces, such as the gastrointestinal, respiratory, and urogenital tracts.
It serves as a defense against infections at mucosal surfaces.
LYMPH NODE
STRUCTURE:
Figure Credit: Jayashree Baidya
1.
Capsule:
·
The outermost
layer of the lymph node is the fibrous capsule.
It provides structural support and helps maintain the shape of the lymph node.
2.
Subcapsular Sinus:
·
This is a space just beneath the capsule
where afferent lymphatic vessels deliver lymph into
the lymph node. It allows for the initial
filtering of the lymph.
3.
Reticular Tissue:
·
Reticular fibers provide a framework within the lymph node. They support and organize the various cells, including
lymphocytes and macrophages.
4.
Lymphocytes and Macrophages:
·
Lymphocytes, including B cells and T
cells and Macrophages are present throughout the
lymph node. These cells play key roles in immune
responses.
5.
Afferent Lymphatic Vessels:
·
Afferent lymphatic vessels bring lymph into the lymph node. They enter the
node at various points, allowing lymph to flow into the lymph node.
6.
Efferent Lymphatic Vessels:
·
Efferent lymphatic vessels carry filtered lymph away from the lymph node.
They typically exit at the hilum.
7.
Hilum:
·
The hilum is a region where blood vessels and efferent lymphatic vessels exit the
lymph node.
FUNCTIONS:
1.
Filtration:
Lymph nodes filter harmful substances, like bacteria and viruses, from the
lymphatic fluid, preventing the spread of infections.
2.
Immune Cell Activation:
Lymph nodes activate immune cells, such as B cells and T cells.
SPLEEN
STRUCTURE:
Figure Credit: Jayashree Baidya
1.
Capsule:
·
Protective outer layer surrounding the
spleen.
2.
Red Pulp:
·
Filters and stores blood, removes old
red blood cells.
3.
White Pulp:
·
Part of the spleen involved in immune
functions, monitors and responds to pathogens.
4.
Hilum:
·
Entry and exit point for blood vessels,
lymphatic vessels, and nerves.
FUNCTIONS:
1.
Blood Cleaner:
·
Filters and cleans the blood by removing
old or damaged red blood cells.
2.
Immune Booster:
·
Supports the immune system by detecting
and responding to pathogens in the blood.
3.
Blood Reservoir:
·
Acts as a storage site for blood,
releasing additional blood cells when needed.