Download The Lymphatic System and Immunity Information

The Lymphatic System and Immunity
The lymphatic system is an extensive drainage network that helps keep
bodily fluid levels in balance and defends the body against infections. The
lymphatic system is made up of a network of lymph nodes, lymph ducts,
and lymphatic vessels. These vessels carry lymph, a clear, watery fluid
containing protein molecules, salts, glucose, urea, and other substances,
throughout the body. One of the lymphatic system's major jobs is to
collect extra lymph fluid from body tissues and return it to the blood. This
process is important because water, proteins, and other substances are
continuously leaking out of tiny blood capillaries into the surrounding body
tissues. If the lymphatic system didn't drain the excess fluid, it would build
up in the body's tissues and they would swell.
The lymphatic system also helps defend the body against germs like
viruses, bacteria, and fungi that can cause illnesses. Those germs are
filtered out in the lymph nodes, which are small masses of tissue (most
lymph nodes are about 1 cm in diameter) located along the network of lymph vessels. The lymph nodes house
lymphocytes (B cells and T cells). Most of the lymph nodes are found in clusters in the neck, armpit, and groin
area. Nodes are also located along the lymphatic pathways in the chest, abdomen, and pelvis, where they filter
the blood.
One of the major lymphatic vessels is the thoracic duct, which
begins near the lower part of the spine and collects lymph from
the pelvis, abdomen, and lower chest. The thoracic duct runs up
through the chest and empties into the blood through a large vein
near the left side of the neck. The right lymphatic duct is the
other major lymphatic vessel. It collects lymph from the right side
of the neck, chest, and arm, and empties into a large vein near the
right side of the neck.
Lymphatic tissue is also scattered throughout the body in different
major organs and in and around the gastrointestinal tract.
How the Lymphatic System Works…
1. Carrying Away Waste
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Lymph fluid drains into tiny vessels called lymph capillaries. The fluid is then pushed along through
the capillaries when a person breathes or the muscles contract. The lymph capillaries are very thin;
they have many tiny openings that let gases, water, and nutrients pass through to the surrounding
cells, nourishing them and taking away waste products. When lymph fluid passes through in this way
it is called interstitial fluid (fluid located in the microscopic places between cells). Lymph vessels
collect the interstitial fluid and then return it to the bloodstream by emptying it into large veins in the
upper chest, near the neck.
2. Fighting Infection
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Lymph fluid enters the lymph nodes, where macrophages fight off foreign bodies like bacteria,
removing them from the bloodstream. After these substances have been filtered out, the lymph fluid
leaves the lymph nodes and returns to the veins, where it reenters the bloodstream.
When a person has an infection, germs collect in the lymph nodes. If the throat is infected, for example, the
lymph nodes of the neck may swell. That's why doctors check for swollen lymph nodes (sometimes called swollen
"glands,” but they're actually lymph nodes) in the neck when your throat is infected.
Major Organs of the Lymphatic System
Tonsils/ Adenoids- Tonsils are lumps of soft tissue
and are part of the immune system. A main
function of tonsils is to trap germs (bacteria and
viruses) which you may breathe in. Proteins called
antibodies produced by the immune cells in the
tonsils help to kill germs and help to prevent throat
and lung infections. Adenoids are made of similar
tissue and they hang from the upper part of the
back of the nasal cavity. Like tonsils, adenoids help
to defend the body from infection. They trap
bacteria and viruses which you breathe in through
your nose and they contain cells and antibodies of
the immune system to help prevent throat and
lung infections.
Spleen- The spleen is the largest organ in the
lymphatic system. It is an important organ for
keeping bodily fluids balanced, but it is possible to live without it. It acts as a filter for blood as part of the
immune system. Old red blood cells are recycled in the spleen, and platelets and white blood cells are stored
there. The spleen also helps fight certain kinds of bacteria.
Appendix- The appendix is a tube-shaped sac that’s attached to the large intestine. The appendix can act as a
reserve for good bacteria. After the immune system fends off disease, the good bacteria emerge and re-colonize
the gut. Lymphoid tissue accumulates in the appendix after birth. In turn, the appendix helps in the maturation
of B lymphocytes and the production of antibodies. The appendix also produces specific molecules that aid in the
movement of lymphocytes to various locations within the body.
Peyer’s Patches- Peyer’s patches are small masses of lymphatic tissue found in the wall of the small intestine.
They form an important part of the immune system by monitoring intestinal bacteria populations and preventing
the growth of pathogenic bacteria in the intestines.
Thymus-The thymus is a lymphoid organ situated in the neck of vertebrates that produces T cells for the immune
system.
Bone Marrow- Bone marrow is the flexible tissue in the interior of bones and it produces the lymphocytes that
support the body's immune system.
Lymph Nodes- As stated earlier, lymph nodes are major sites of B and T lymphocytes, and other white blood cells.
Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles
and cancer cells.
The Immune System
The immune system, which is made up of special cells, proteins, tissues, and organs, defends people against
germs and microorganisms every day. In most cases, the immune system does a great job of keeping people
healthy and preventing infections. But sometimes, problems with the immune system can lead to illness and
infection.
The immune system is the body's defense against infectious organisms and other invaders. Through a series of
steps called the immune response, the immune system attacks organisms and substances that invade our systems
and cause disease.
Cells
The cells that are part of this defense system include white blood cells (WBC’s), also called leukocytes. They seek
out and destroy the organisms or substances that cause disease. There are several different types of white cells
which work together to seek out and destroy bacteria and viruses. All of them start off in the bone marrow,
growing from 'stem cells'. The disease-fighting white blood cells are specialists and have a specific job.
Among your white blood cells are the following:
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Neutrophils- They kill and digest bacteria and fungi. They are the most numerous type of white blood
cells and your first line of defense when infection strikes.
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Monocytes- They have a longer lifespan than many white blood cells and help to break down bacteria.
They present pieces of pathogens to T cells so that the pathogens may be recognized again and killed.
This causes an antibody response to be mounted. Monocytes eventually leave the bloodstream and
become macrophages, the biggest type of white blood cell and their job is to eat foreign material in the
body.
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Basophils- These small cells appear to sound an alarm
when infectious agents invade your blood. They secrete
chemicals such as histamine, a marker of allergic disease,
that help control the body's immune response.
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Eosinophils- They attack and kill parasites, destroy cancer
cells, and help with allergic responses.
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Lymphocytes- They create antibodies to defend against
bacteria, viruses, and other potentially harmful invaders.
There are two kinds of lymphocytes: B lymphocytes (B cells) and T lymphocytes (T cells). Lymphocytes
start out in the bone marrow and either stay and mature there to become B cells or leave for the thymus
gland, where they mature to become T cells.
Functions of B cells and T cells:
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B cells produce antibodies. Each cell watches out for a particular germ, and when that germ
arrives, the B cells starts to produce more antibodies which begin the process of killing that germ.
Antibodies attach themselves to the germs so that other cells can recognize that these germs
need to be destroyed.
o
T cells look for cells in your body that are hiding invaders (germs) or body cells that are different
to normal healthy cells (such as cells that could develop into a cancer) and kill them. There are
two different kind of T cells including:
1. Natural Killer T Cells- cell that can react against and destroy another cell without prior
sensitization to it.
2. Helper T cells- cells that identify invaded cells and send out chemicals as an alarm, telling
killer T-cells to multiply.
Locations of White Blood Cells (WBC’s)
Leukocytes (WBC’s) are produced and stored in many locations
throughout the body, including the tonsils, adenoids, lymph
nodes, thymus, spleen, appendix, Peyer’s patch, and bone
marrow. For this reason, they are called the lymphoid organs.
There are also clumps of lymphoid tissue throughout the body,
primarily in the form of lymph nodes, that house the WBC’s.
The WBC’s circulate through the body between the organs and
nodes by means of the lymphatic vessels. (You can think of the
lymphatic vessels as a type of highway between the rest stops
that are the lymphoid organs and lymph nodes.). WBC’s can
also circulate through the blood vessels. In this way, the
immune system works in a coordinated manner to monitor the
body for germs or substances that might cause problems.
Here's how it works:
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A foreign substance that invades the body is called
an antigen (think of this as a germ- virus, bacterial infection, etc.). When an antigen is detected, the
immune system is activated and WBC’s are sent to determine what has invaded your body.
The WBC’s need more specialized cells to help, so they chemically notify the T cells.
The T cells send for the B cells which have the ability to
produce protein strands called antibodies. Antibodies
are specialized proteins that lock onto specific antigens.
Antibodies and antigens fit together like a key and a lock.
Once the B cells recognize specific antigens, they develop
a memory for the antigen and will produce antibodies
the next time the antigen enters a person's body. That's
why if someone gets sick with a certain disease, like
chickenpox, that person typically doesn't get sick from it
again. This is also why we use immunizations to prevent
certain diseases. The immunization introduces the body
to the antigen in a way that doesn't make a person sick,
but it does allow the body to produce antibodies that will
then protect that person from future attack by the germ or substance that produces that particular
disease.
Although antibodies can recognize an antigen and lock onto it, they are not capable of destroying it
without help. That is the job of the T cells. The T cells that destroy antigens that have been tagged by
antibodies or cells that have been infected or somehow changed. T cells are also involved in helping
signal other cells to do their jobs.
Antibodies can also neutralize toxins (poisonous or damaging substances) produced by different
organisms. Lastly, antibodies can activate a group of proteins called complement that are also part of
the immune system. Complement assists in killing bacteria, viruses, or infected cells. All of these
specialized cells and parts of the immune system offer the body protection against disease. This
protection is called immunity.
Here is my visual aid to guide you:
Germ (antigen) enters the body
The White Blood Cells are sent to
investigate what has invaded your body
The White Blood Cells need more specialized help, so they notify
the T cells
The T cells send for the B cells because the B cells produce antibodies to fight the germ
The antibodies, with the help of the T cells, go to work to fight off the antigen!
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