The lymphatic system
Your lymphatic system is part of your immune
system and has many functions
These functions include:
protecting your body from infection -
the lymphatic system is part of the immune system. It
produces and releases lymphocytes (white blood cells) and
other immune cells that monitor and then destroy the foreign
pathogen invaders that may enter your body e.g. bacteria,
viruses, parasites and fungi.
maintaining body fluid levels - the
lymphatic system collects excess fluid that drains from
cells and tissue throughout your body and returns it into
your bloodstream, which is recycled through your body.
absorbing digestive tract fats -
lymph includes fluids from your intestines that contain
fats and proteins and transports it back into your
bloodstream.
removing cellular waste - lymph
fluids transports and removes waste products and abnormal
cells.
Blockages, diseases or infections can
impair your lymphatic system’s function.
The main parts of the Lymphatic system
1. Lymph (lymphatic fluid)
Lymph is a collection of the extra fluid
that drains from cells and tissues (that is not reabsorbed
into the capillaries) and contains other substances such as
proteins, minerals, fats, nutrients, damaged cells, cancer
cells and foreign invaders (bacteria, viruses, etc). Lymph
also transports infection-fighting white blood cells (lymphocytes).
2. Lymph nodes
Lymph nodes are bean-shaped glands of
lymphatic tissue, found throughout the lymphatic system
(particularly the neck and armpits), that monitor and
cleanse the lymph fluid as it filters through them.
Large numbers of lymphocytes are found in
the lymph nodes. Tissues such as bone marrow, are associated
with the lymphatic system and produce these lymphocytes
which play an important role in defending the body against
infections (e.g. pathogens).
The lymph nodes filter out the damaged cells
and cancer cells and also store lymphocytes and other immune
system cells that attack and destroy bacteria and other
harmful substances in the fluid.
3. Lymphatic vessels and collecting ducts
Lymphatic vessels are the network of
capillaries and a large network of fine tubes located
throughout your body that transport lymph away from tissues
back to the heart and connects with the blood system near
the heart where lymph fluids is returned to the blood
plasma.
Lymphatic vessels collect and filter lymph
fluid (at the nodes, see above) as it continues to move
toward larger vessels called collecting ducts. These
lymphatic vessels operate very much like blood veins do, but
work under very low pressure, and have a series of valves in
them to keep the fluid moving in one direction. The
collecting ducts return lymph to the bloodstream which helps
to maintain normal blood volume and pressure and also
prevents the excessive build up of fluid around the tissues.
4. Spleen
The spleen is the largest lymphatic organ is
located under your ribs and above your stomach. The spleen
filters and stores blood and produces white blood cells to
fight infection or disease.
5. Thymus
This thymus organ is located in the upper
chest beneath the breast bone and its function is to mature
a specific type of white blood cell that fights off
pathogens.
6. Tonsils and adenoids
These lymphoid organs trap pathogens from
the food you eat and the air you breathe and they are your
body’s first line of defence against pathogens.
7. Bone marrow
Bone marrow is the soft, spongy tissue in
the centre of certain bones, such as the hip bone and
breastbone. White blood cells, red blood cells, and
platelets are all made in the bone marrow.
8. Peyer's patches
Peyer's patches are small masses of
lymphatic tissue in the mucous membrane that lines your
small intestine and these lymphoid cells monitor and
destroy bacteria in the intestines.
9. Appendix
Your appendix contains lymphoid tissue that
can destroy bacteria before it breaches the intestine wall
during absorption of food from digestion. The appendix
may play a role in housing 'good bacteria' and
repopulating our gut with good bacteria after an infection
has cleared.
A
note on transportation - function of the lymphatic system in the
circulation of body fluids
The walls of the associated capillaries are
very thin and water, so dissolved solutes and dissolved
gases can diffuse in and out of them and pass through the
walls from the plasma into the tissue fluid surrounding the
cells
Cells can exchange materials such as water,
oxygen, glucose, amino acids, carbon dioxide, mineral ions
(e.g. K+, Na+, Cl-, Ca2+
etc.) out through their cell membranes into the tissue fluid
surrounding them (either by diffusion, osmosis or active
transport).
More fluid leaks out of the capillaries than
is returned to them, and the excess leaked fluid surrounding
the capillaries passes into the lymphatic system and becomes
part of the lymph fluid.
Reminders:
Phagocytes (see
part 5) can leave the
bloodstream and squeeze through capillaries and enter tissues
attacked by some invasive pathogen infection.
The phagocytes move to
the pathogens (or toxins) and ingest them.
When we suffer from a disease that we recover
from, the body makes memory cells that recognise the same
infection if it enters the body again.
The memory cells produce antibodies to destroy
the pathogen, hopefully to prevent us from feeling or being ill
- we may be completely unaware that this has happened.
All invading cells have unique
molecules ('molecular structure') on their surface called antigens.
When white cells encounter a
'foreign' antigen on a pathogen they don't recognise, they produce proteins
called antibodies which lock onto the antigens of the pathogen making
them more susceptible to phagocytosis - described above and
also inhibit the pathogen from entering your cells.
Reminder: The pathogen can
be a bacteria, virus or fungus.
The white blood cells that
perform this task are called B-lymphocytes and the overall
process is described using
the diagram below.
These cells are
involved with specific immune responses which can involves
various mechanisms after the lymphocytes recognise pathogens and
quickly reproduce to make lots of antibodies e.g.
The antibodies can cause
pathogen cells to burst - a process called lysis, often due
to an enzymic action.
The antibodies can bind
to pathogens and destroy them.
The antibodies coat the
pathogen, sticking them together so that phagocytes can
ingest them.
1. Large numbers
of B-lymphocyte white blood cells (grey) are always present
in the blood and they can recognise OR not recognise, different
types of pathogens - bacteria and viruses.
2.
All invading pathogens (green
O) have unique molecules on their surface called antigens (blue
-, often proteins). If the surface of the lymphocyte detects the
antigens (blue) on the surface of a 'foreign' pathogen they don't
recognise, a response is triggered by the lymphocyte cell.
3.
The lymphocyte cell begins to produce protein molecules called antibodies (black Y).
4.
The antibodies move out of the cell to 'confront' the invading
pathogen and will not lock onto any other pathogen.
5.
The antibodies lock onto the antigens on the surface of the
pathogen (e.g. invading bacteria cell).
6. The invasive
pathogen is then more easily found and destroyed by another type of
white blood cell - the phagocytes, which destroy them by
phagocytosis - described in section (a) above.
The antibodies often cause
the pathogens to clump together making it easier for the
phagocyte cells to find and ingest them by phagocytosis.
The white blood cells that
detect the pathogen then divide to produce more copies (clones)
of the same white blood cell, which in turn make more of the
antibody.
The antibodies are produced
quite rapidly and move all around the body in the bloodstream to
find other similar pathogens.
If exactly the same type of
pathogen enters your body again, the lymphocyte cells recognise it
immediately and make lots of antibodies to counteract it.
This the basis of immunity
i.e. how you become immune from a disease and this is described
in detail in the next section.
