Anatomy of the Lymphatic and Immune Systems
The immune system is the complex collection of cells and organs that destroys or neutralizes
pathogens that would otherwise cause disease or death. The lymphatic system, for most
people, is associated with the immune system to such a degree that the two systems are
virtually indistinguishable. The lymphatic system is the system of vessels, cells, and organs that
carries excess fluids to the bloodstream and filters pathogens from the blood. The swelling of
lymph nodes during an infection and the transport of lymphocytes via the lymphatic vessels are
but two examples of the many connections between these critical organ systems.
Functions of the Lymphatic System
A major function of the lymphatic system is to drain body fluids and return them to the
bloodstream. Blood pressure causes leakage of fluid from the capillaries, resulting in the
accumulation of fluid in the interstitial space—that is, spaces between individual cells in the
tissues. In humans, 20 liters of plasma is released into the interstitial space of the tissues each
day due to capillary filtration. Once this filtrate is out of the bloodstream and in the tissue
spaces, it is referred to as interstitial fluid. Of this, 17 liters is reabsorbed directly by the
blood vessels. But what happens to the remaining three liters ? This is where the lymphatic
system comes into play. It drains the excess fluid and empties it back into the bloodstream via
a series of vessels, trunks, and ducts. Lymph is the term used to describe interstitial fluid once it
has entered the lymphatic system. When the lymphatic system is damaged in some way, such
as by being blocked by cancer cells or destroyed by injury, protein-rich interstitial fluid
accumulates (sometimes “backs up” from the lymph vessels) in the tissue spaces. This
inappropriate accumulation of fluid referred to as lymphedema may lead to serious medical
consequences.
As the vertebrate immune system evolved, the network of lymphatic vessels became convenient
avenues for transporting the cells of the immune system. Additionally, the transport of dietary
lipids and fat-soluble vitamins absorbed in the gut uses this system.
Cells of the immune system not only use lymphatic vessels to make their way from interstitial
spaces back into the circulation, but they also use lymph nodes as major staging areas for the
development of critical immune responses. A lymph node is one of the small, bean-shaped
organs located throughout the lymphatic system.
Structure of the Lymphatic System
The lymphatic vessels begin as open-ended capillaries, which feed into larger and larger
lymphatic vessels, and eventually empty into the bloodstream by a series of ducts. Along the
way, the lymph travels through the lymph nodes, which are commonly found near the groin,
armpits, neck, chest, and abdomen. Humans have about 500–600 lymph nodes throughout the
body.
Figure : Lymphatic vessels in the arms and legs convey lymph to the larger lymphatic vessels in the torso.
, A major distinction between the lymphatic and cardiovascular systems in humans is that lymph
is not actively pumped by the heart, but is forced through the vessels by the movements of the
body, the contraction of skeletal muscles during body movements, and breathing. One-way
valves (semi-lunar valves) in lymphatic vessels keep the lymph moving toward the heart. Lymph
flows from the lymphatic capillaries, through lymphatic vessels, and then is dumped into the
circulatory system via the lymphatic ducts located at the junction of the jugular and subclavian
veins in the neck.
Lymphatic Capillaries
Lymphatic capillaries, also called the terminal lymphatics, are vessels where interstitial fluid
enters the lymphatic system to become lymph fluid. Located in almost every tissue in the body,
these vessels are interlaced among the arterioles and venules of the circulatory system in the
soft connective tissues of the body. Exceptions are the central nervous system, bone marrow,
bones, teeth, and the cornea of the eye, which do not contain lymph vessels.
Lymphatic Capillaries Lymphatic capillaries are interlaced with the arterioles and venules of the
cardiovascular system. Collagen fibers anchor a lymphatic capillary in the tissue (inset). Interstitial fluid slips through
spaces between the overlapping endothelial cells that compose the lymphatic capillary.
Lymphatic capillaries are formed by a one cell-thick layer of endothelial cells and represent
the open end of the system, allowing interstitial fluid to flow into them via overlapping cells .
The immune system is the complex collection of cells and organs that destroys or neutralizes
pathogens that would otherwise cause disease or death. The lymphatic system, for most
people, is associated with the immune system to such a degree that the two systems are
virtually indistinguishable. The lymphatic system is the system of vessels, cells, and organs that
carries excess fluids to the bloodstream and filters pathogens from the blood. The swelling of
lymph nodes during an infection and the transport of lymphocytes via the lymphatic vessels are
but two examples of the many connections between these critical organ systems.
Functions of the Lymphatic System
A major function of the lymphatic system is to drain body fluids and return them to the
bloodstream. Blood pressure causes leakage of fluid from the capillaries, resulting in the
accumulation of fluid in the interstitial space—that is, spaces between individual cells in the
tissues. In humans, 20 liters of plasma is released into the interstitial space of the tissues each
day due to capillary filtration. Once this filtrate is out of the bloodstream and in the tissue
spaces, it is referred to as interstitial fluid. Of this, 17 liters is reabsorbed directly by the
blood vessels. But what happens to the remaining three liters ? This is where the lymphatic
system comes into play. It drains the excess fluid and empties it back into the bloodstream via
a series of vessels, trunks, and ducts. Lymph is the term used to describe interstitial fluid once it
has entered the lymphatic system. When the lymphatic system is damaged in some way, such
as by being blocked by cancer cells or destroyed by injury, protein-rich interstitial fluid
accumulates (sometimes “backs up” from the lymph vessels) in the tissue spaces. This
inappropriate accumulation of fluid referred to as lymphedema may lead to serious medical
consequences.
As the vertebrate immune system evolved, the network of lymphatic vessels became convenient
avenues for transporting the cells of the immune system. Additionally, the transport of dietary
lipids and fat-soluble vitamins absorbed in the gut uses this system.
Cells of the immune system not only use lymphatic vessels to make their way from interstitial
spaces back into the circulation, but they also use lymph nodes as major staging areas for the
development of critical immune responses. A lymph node is one of the small, bean-shaped
organs located throughout the lymphatic system.
Structure of the Lymphatic System
The lymphatic vessels begin as open-ended capillaries, which feed into larger and larger
lymphatic vessels, and eventually empty into the bloodstream by a series of ducts. Along the
way, the lymph travels through the lymph nodes, which are commonly found near the groin,
armpits, neck, chest, and abdomen. Humans have about 500–600 lymph nodes throughout the
body.
Figure : Lymphatic vessels in the arms and legs convey lymph to the larger lymphatic vessels in the torso.
, A major distinction between the lymphatic and cardiovascular systems in humans is that lymph
is not actively pumped by the heart, but is forced through the vessels by the movements of the
body, the contraction of skeletal muscles during body movements, and breathing. One-way
valves (semi-lunar valves) in lymphatic vessels keep the lymph moving toward the heart. Lymph
flows from the lymphatic capillaries, through lymphatic vessels, and then is dumped into the
circulatory system via the lymphatic ducts located at the junction of the jugular and subclavian
veins in the neck.
Lymphatic Capillaries
Lymphatic capillaries, also called the terminal lymphatics, are vessels where interstitial fluid
enters the lymphatic system to become lymph fluid. Located in almost every tissue in the body,
these vessels are interlaced among the arterioles and venules of the circulatory system in the
soft connective tissues of the body. Exceptions are the central nervous system, bone marrow,
bones, teeth, and the cornea of the eye, which do not contain lymph vessels.
Lymphatic Capillaries Lymphatic capillaries are interlaced with the arterioles and venules of the
cardiovascular system. Collagen fibers anchor a lymphatic capillary in the tissue (inset). Interstitial fluid slips through
spaces between the overlapping endothelial cells that compose the lymphatic capillary.
Lymphatic capillaries are formed by a one cell-thick layer of endothelial cells and represent
the open end of the system, allowing interstitial fluid to flow into them via overlapping cells .
