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LEVEL 3 DIPLOMA IN AROMATHERAPY
MODULE 16
KNOWLEDGE OF ANATOMY, PHYSIOLOGY & PATHOLOGY FOR
COMPLEMENTARY THERAPIES
THE LYMPHATIC & IMMUNE SYSTEM
MODULE 9
COURSE MANUAL
CHRISTINA LYNE
[email protected]
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THE LYMPHATIC SYSTEM
The lymphatic system is a network of lymph vessels, nodes and ducts that stretches
throughout the entire body. Lymph flows through this system.
The main function of the lymphatic system is to drain fluid from the spaces between
cells in order to filter out waste and toxins, destroy foreign particles and prevent
infection.
The lymphatic system is made up of the following:
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Lymph
Lymphatic capillaries
Lymphatic vessels
Lymph nodes
Lymphatic ducts
Areas of lymph tissue - thymus gland, spleen, tonsils and adenoids
Areas of specialist lymph tissue - lacteals and Peyer’s patches
Our body actually has two circulatory systems. While they work individually to
perform their main functions, they also work together to some degree. One of these,
the Cardiovascular System, provides our body tissues with the needed oxygen,
nutrients, and hormone-rich blood required for everyday functions. The other, the
Lymphatic System, rids our body of the waste products (including old red blood
cells) produced during daily internal functions, thus protecting us from the harmful
effects we would experience otherwise. In addition, the spleen (part of the
Lymphatic System) also serves as a blood reservoir for the Cardiovascular System
until the blood is needed.
The Cardiovascular System is related to the Lymphatic System. In the Cardiovascular System, blood is the vehicle used to deliver oxygen, nutrients and hormones to
the various muscle and organ tissues within the body. Arteries deliver this loaded
blood into the various body parts, using capillaries for some of the delivery. Then,
the veins return the depleted blood back to the heart for oxygenation again.
While the kidneys serve as the main blood cleaning station in the body, removing
waste and fluid excess from it, the Lymphatic System also plays a role in the purifying of the blood. It removes the old red blood cells and any wayward blood that may
have seeped into muscle tissues accidentally during transit through the body.
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WHAT IS LYMPH? - Lymph is the fluid that flows through the lymphatic system.
Lymph is a pale milky-coloured fluid. Its composition is very similar to that of blood
plasma, but it contains less protein than plasma. Lymph has no red blood cells, but
does contain white blood cells called lymphocytes. As it flows around the body,
lymph picks up bacteria and cell debris from damaged tissues, which are then
filtered out and destroyed as they pass through the lymph nodes.
Lymph contains many dissolved substances and the remains of micro-organisms
that invade the body. It will also contain protein molecules that are too large to pass
through blood capillary walls, and fat molecules that have been absorbed through
lacteals that line the small intestine walls.
HOW IS LYMPH FORMED?
It is formed by plasma (the liquid part of blood) seeping out of the capillaries. This
tissue fluid or interstitial fluid bathes all the tissue cells. As it does this, it acts as a
medium of exchange i.e. it transfers food, oxygen and water (nutritive materials) and
receives urea and carbon dioxide (waste products) in return. It creates the
environment that cells need to survive.
Each day about 20 litres of fluid filter from blood into tissue spaces. About 85% of
this fluid is returned to the blood system. The remaining 15% enters the lymphatic
vessels and becomes lymph.
LYMPH CAPILLARIES - these are located throughout the body
Lymphatic capillaries are slightly larger than blood capillaries and have a unique
structure that permits interstitial fluid to flow into them but not out. They are closedended vessels and their walls are made up of endothelial cells enabling them to
soak up proteins and cell debris. Lymphatic capillaries unite to form larger and
larger lymph vessels.
LYMPH VESSELS - tubes that carry lymph
Lymph vessels often lie close to arteries and veins. These thin-walled collapsible
tubes are structurally similar to veins - they are made up of the same layers of
tissue: a fibrous covering, a middle layer of smooth muscle and elastic tissue and
an inner lining of endothelium. The function of these vessels is to transport lymph
from the capillaries to lymph nodes.
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HOW LYMPH MOVES THROUGH THE LYMPHATIC VESSELS
The lymphatic system, unlike the circulatory system, has no pump. Like veins, lymph
vessels have numerous cup-shaped valves that ensure that the lymph flows in one
direction and that the backward flow is avoided. The larger lymph vessels have a
smooth muscle layer in the walls, which contract rhythmically (the lymphatic pump)
and this is how lymph is pushed towards the heart.
Additionally, lymph moves through the vessels with the help of a:
skeletal muscle pump - when the muscles contract they compress the lymphatic
vessels and force the lymph towards the subclavian veins. The valves ensure the
lymph flows in one direction only.
respiratory pump - pressure changes occur during inhalation. Lymph flows from
the abdominal region, where the pressure is higher, toward the thoracic region,
where the pressure is lower. When the pressures reverse during exhalation, the
valves prevent the backflow of lymph.
LYMPH NODES or GLANDS
Lymph nodes are often referred to as lymph glands, even though they are
non-secretory. They vary considerably in size: some as small as a pin head and the
largest are about the size of an almond.
Lymph nodes are composed of reticular and lymphatic tissue. They are enclosed in
a tough fibrous capsule made of dense connective tissue and are usually found
embedded in fat. Each node has an outer cortex and inner medulla containing
numerous lymphocytes and macrophages which help to carry out the cleaning-up
process. As many as five or six afferent vessels will bring lymph to a node while
only one or two efferent lymph nodes carry lymph out of the node. An artery enters
and a vein leaves the node.
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Lymph is filtered very slowly, allowing foreign substances to become trapped by
reticular fibres within the lymphatic sinuses or trabeculae. Macrophages, antibodies
and lymphocytes within the node then destroy the foreign substances. Lymph
passes through several lymph nodes (usually about 8 – 10 times) where it is filtered
before being returned to the venous bloodstream. Approximately 2 - 4 litres of
lymph are filtered back into the venous bloodstream every day.
Swollen lymph nodes commonly indicate disease. During an infection, they may
swell, become inflamed and tender. This swelling may be noticeable even before
the infection itself is apparent. E.g. swelling of the glands in the side of the neck
during a throat infection is a common experience - a condition called ‘swollen
glands‘.
The function of lymph nodes is to filter lymph and remove / destroy harmful substances before it is returned to the bloodstream.
LOCATION OF MAJOR LYMPH NODES IN THE BODY
There are numerous lymph nodes situated along the length of lymph vessels, and
are arranged in deep and superficial groups. The main areas are in the neck, armpit,
breast, abdomen, groin and behind the knee. They are:
Submandibular – these are situated just under the jaw and filter lymph from the
head and neck areas.
Deep / superficial cervical - these are situated in the neck and filter lymph from the
head, tongue and mouth.
Axillary - these are situated under the arms and filter lymph from the upper limbs
and breast areas.
Iliac - these are situated mainly in association with the blood vessels supplying the
abdominal organs.
Supratrochlear - these are situated in the elbow joint and filter lymph from the
upper limbs.
Inguinal - these are situated in the groin and filter lymph from the lower limbs.
Popliteal - these are situated in the knee joint and filter lymph from the lower legs.
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THE LYMPHATIC DUCTS
The lymph vessels get larger as they join together, until finally the fluid is carried to
the two largest vessels called lymph ducts: the thoracic duct and the right lymphatic
duct.
After being filtered thoroughly by the nodes, lymph is emptied into these ducts and is
then returned to the bloodstream via the subclavian veins. This is how lymph drains
back into blood.
THE THORACIC DUCT
This is the largest lymph vessel in the body through which most of the lymph flows.
It commences at the cisterna chyli, which is a lymph vessel situated in front of the
first two lumbar vertebrae. The duct is approx. 40 cm long and opens into the left
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subclavian vein situated at the base of the neck. It drains lymph from both legs, the
pelvic and abdominal cavities, the left half of the head, neck, chest and left arm.
THE RIGHT LYMPHATIC DUCT
This is the smaller of the 2 ducts, measuring approx. 1 cm long. It is also situated at
the base of the neck and opens into the right subclavian vein. It drains lymph from
the right half of the head, neck, right arm and chest.
FUNCTIONS OF THE LYMPHATIC SYSTEM
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It transfers nutritive materials to the cells i.e. food, oxygen and water, allowing
the body to grow and work with other body systems to function efficiently.
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It removes waste products from the cells i.e. urea and carbon dioxide.
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It filters lymph to remove and purify it from unwanted matter.
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It produces anti-bodies, thus helping to fight infection.
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It assists in the maintenance of bone and muscle repair after injury.
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It produces lymphocytes to help protect the body from foreign cells, microbes
and cancer cells.
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It drains interstitial fluid from the tissues (this helps with the prevention of
oedema).
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Lacteals absorb dietary lipids (triglycerides & cholesterol) and fat-soluble
vitamins (A, D, E, and K) from the villi in the gastrointestinal tract to the blood.
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AREAS CONTAINING LYMPHATIC TISSUE
Lymphatic tissue contains many types of cells, the principal one being the lymphocyte. This white blood cell is made in the bone marrow. Once released into the
bloodstream from the bone marrow, lymphocytes are further processed to make two
functionally distinct types: the T-lymphocyte and the B-lymphocyte.
T-lymphocytes:
These are processed in the thymus gland. The hormone thymosin is responsible
for the development of lymphocytes into fully specialised, mature, functional Tlymphocytes. A mature T-lymphocyte will recognise only one type of antigen and will
not recognise or attack any other, no matter how dangerous it might be.
B-lymphocytes:
These are produced and processed in bone marrow. They produce antibodies
(immunoglobulins) which are proteins designed to bind to and destroy an antigen.
They function in the same way as T-lymphocytes in that they will only recognise and
react with one type of antigen and no other.
Lymphatic tissue is the main tissue in lymph nodes and lymphatic nodules
and is found in the tonsils and adenoids, thymus, spleen, digestive, respiratory,
urinary and reproductive tracts.
THE THYMUS GLAND
The thymus is situated behind the sternum, or breastbone, in the upper part of the
chest. It lies very close to the heart in the thoracic cavity.
It consists of two lobes joined by areolar tissue. A layer of connective tissue covers
each lobe. The lobes are enclosed by a fibrous capsule which is further divided into
lobules that are made up of an irregular branching framework of epithelial
cells. Each lobule has a dense concentration of immature T- lymphocytes.
FUNCTIONS OF THE THYMUS GLAND
Before birth, small, medium and large lymphocytes migrate to the thymus. They develop into T-cells and will attack foreign cells. From there they go to the lymph nodes
where they are stored or released when required to provide immunity. The epithelial cells secrete the hormone thymosin, which stimulates general growth and is involved in processing and stimulating lymphocytes to reproduce in lymphoid tissue.
T-cells include:
Helper cells - they help B-cells and feeding cells
Killer cells - they kill the body's own cells that have been invaded by antigens and also kill tumour cells in the body
Suppressor cells - they suppress over-aggressive lymphocytes.
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THE SPLEEN
The spleen is the largest lymph organ in the body. It is a dark, purplish oval organ
that lies behind the stomach and beneath the diaphragm. It is composed of reticular
fibres and fibroblasts through which trabeculae extend. The bulk (pulp) of the organ
is composed of two types: white pulp and red pulp. The white pulp is composed of
lymphatic nodules and the red pulp consists of blood sinuses lined with epithelial
cells. The red pulp is the portion of the spleen which functions to filter the blood and
remove worn-out erythrocytes with the help of macrophages before it is delivered to
the liver. It is covered by a capsule of dense connective tissue.
The spleen is not exposed to infections carried or spread by lymph, because it does
not filter lymph.
Structures entering and leaving the spleen are:
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Splenic artery
Splenic vein - a branch of the portal vein
Lymph vessels (efferent only)
Nerves
FUNCTIONS OF THE SPLEEN
The spleen controls the quality and quantity of blood in circulation.
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Worn-out erythrocytes are destroyed in the spleen and the breakdown
products - bilirubin and iron - are passed to the liver via the splenic vein.
Leukocytes, platelets and microbes are engulfed by phagocytes present in
the spleen.
Acts as a reservoir for all types of blood cells. Can contain up to 350mls of
blood.
Contains T and B lymphocytes, which are activated in the presence of
antigens e.g. in infection. Lymphocyte proliferation during serious infection
can cause enlargement of the spleen (splenomegaly)
Platelets live between 8 - 11 days in the spleen and promote blood clotting.
Those not used are destroyed by spleen cells.
Produces foetal blood cells.
LYMPHATIC NODULES
The tonsils and adenoids are made of oval-shaped concentrations of lymphatic
tissue that are strategically positioned to protect against ingested or inhaled
organisms which attempt to enter the digestive and respiratory tracts.
They are found in the connective tissue of mucous membranes lining the respiratory
and digestive tracts. They are not surrounded by a capsule.
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THE TONSILS
The tonsils are two almond-shaped glands consisting of a mass of lymphatic tissue
covered by a mucous membrane. Running through the mucosa of each tonsil are
pits, called crypts. There are two tonsils (palatine tonsils) at the back of the roof of
the mouth, and a smaller pair (lingual tonsils) at the base of the tongue. They help
to protect the throat and airways from infection.
THE ADENOIDS
This is a mass of lymphatic tissue at the rear of the nasal cavity. The surfaces are
composed of ciliated epithelium and are covered by a thin film of mucus. The two
adenoids protect the upper part of the respiratory tract. When they become
swollen, the connection between the nose and throat narrows and it is this that
affects the voice, giving a nasal or "adenoidal" sound.
SPECIALIST LYMPH TISSUE
LACTEALS
The lacteals are a network of lymph and blood capillaries that lie inside projections
called villi on the wall of the small intestine. Each villi is covered by a layer of
epithelial cells. These cells also have projections called microvilli and together the
villi and microvilli increase the surface area of the small intestine for maximum and
efficient absorption of nutrients.
Lacteals collect microscopic globules of fat from the small intestine. The fat then
travels through the lymphatic system and is slowly emptied into the bloodstream.
This process gives the lymph a milky appearance. Lymph entering the thoracic duct
from the small intestine is called chyle.
PEYER’S PATCHES
There are numerous, smaller lymph nodes found in the mucous membrane at
irregular intervals throughout the length of the small intestine. The larger nodes
called Peyer’s patches are found in the lower part of the small intestine (ileum).
These clusters of protective lymphatic tissue are packed with defensive cells, and
are strategically placed to intercept ingested antigens.
APPENDIX
This is found at the end of the small intestine (at the end of the caecum).
Its function is unknown.
BODY FLUIDS
An important aspect of homeostasis is maintaining the volume and composition of
body fluids, which are dilute, watery solutions found inside cells as well as
surrounding them.
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About two thirds of body fluid is intracellular fluid and this is found inside
cells.
The other third, called extracellular fluid, is found outside body cells and
includes all other body fluids.
About 80% of extracellular fluid is interstitial fluid - this is the fluid that
occupies the microscopic spaces between tissue cells.
20% of extracellular fluid is plasma.
Extracellular fluid:
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within blood vessels is called plasma
within the lymphatic vessels is called lymph
within joints is called synovial fluid
in and around the brain and spinal cord is called cerebrospinal fluid
Both interstitial and intracellular fluid are made up of oxygen, nutrients, waste and
other particles dissolved in water.
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THE IMMUNE SYSTEM
The immune system is a collection of special cells that help the body to resist
infection and to defend itself against particular invading antigens. Antigens are
molecules (usually proteins) on the surface of cells, viruses, fungi or bacteria. Non
living substances such as toxins, chemicals, drugs and foreign particles (such as a
splinter) can be antigens. The immune system recognises and destroys substances
that contain these antigens.
Definition of Immune response: The immune response is how the body
recognises and defends itself against bacteria, viruses and substances that appear
foreign and harmful to the body.
Primary immune response
When the immune system meets an antigen for the first time, antibodies are
produced. This can sometimes take a few days to trigger and the disease may
already have developed.
Secondary immune response.
Should the same antigens invade again however, the body then produces the
antibodies very quickly, and in much larger amounts. Because the response is more
immediate the second time around, the body rarely suffers the same disease again.
INNATE IMMUNITY
Innate immunity is a defensive system that we are born with. It protects us against
all antigens. Innate immunity involves barriers that keep harmful materials from
entering the body. These barriers form the first line of defense in the immune
response. The following are examples of innate immunity:
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Cilia in the nose prevent entry of dust and micro-organisms.
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Sneezing helps to expel foreign material from the respiratory tract.
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Breast feeding transfers antibodies from mother to newborn baby.
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Tears contain a bacterial-killing enzymes called lysozyme.
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Saliva in the mouth washes away food debris to discourage bacterial growth.
It also contains the enzyme lysozyme which attacks bacteria.
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Hydrochloric acid found in gastric juice is strongly acidic and kills the
majority of ingested microbes.
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Sebum is an oily substance secreted by sebaceous glands in the skin. The
unsaturated fatty acids in sebum inhibit the growth of certain bacteria and
fungi.
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Beneficial (good) bacteria in the intestines control harmful organisms.
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Mucus helps to trap many microbes and foreign substances.
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Vaginal and penile secretions are slightly acidic, which discourages
bacterial growth.
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Perspiration contains the antibacterial fluid lysozyme which helps to wash
away microbes found on the skin’s surface.
ACQUIRED IMMUNITY
This is immunity that develops with exposure to various antigens. Immunity may be
acquired naturally or artificially and both forms may be active or passive. It is not
innate and is obtained over a lifetime.
NATURALLY ACQUIRED PASSIVE IMMUNITY - this is the transference of
antibodies obtained from the mother through the placenta to the foetus or to the
infant through colostrum and breast milk.
NATURALLY ACQUIRED ACTIVE IMMUNITY - if foreign substances (antigens)
come into contact with the skin or the lining of the nose, mouth, eyes or
gastrointestinal tract, the immune system will respond by producing its own
antibodies.
ARTIFICIALLY ACQUIRED PASSIVE IMMUNITY - the body is given (injected with)
antibodies which induces an active immune response but does not make the person
ill. A new-born has passive immunity to several diseases such as measles, mumps
and rubella, transferred through the placenta from the mother. These antibodies
disappear between 6 to 12 months, which is why MMR is given just after a child's
first birthday.
ARTIFICIALLY ACQUIRED ACTIVE IMMUNITY - when a vaccine triggers the
immune system to produce antibodies against a disease as though the body had
been infected with it. This also teaches the body’s immune system how to produce
appropriate antibodies quickly. If the immunised person then comes into contact
with the disease itself, their immune system will recognise it and immediately
produce the antibodies needed to fight it.
BLOOD COMPONENTS & THE ALLERGIC RESPONSE
An antigen is any substance that the body regards as foreign. Once the body
decides it is an antigen, the immune system will mount a response. The immune
system contains certain types of white blood cells. There are two types of
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lymphocytes (white blood cells) and these are responsible for responding to
antigens:
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B cells are formed in red bone marrow. These attach to a specific antigen
and this helps to destroy it more easily. They secrete antibodies.
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T cells are formed in red bone marrow, and then move to the thymus gland to
mature. Here they develop antigen receptors enabling them to recognise
specific antigens. There are two types of T cells: CD4+ cells and CD8+ cells.
Both B cells and T cells respond differently to pathogens. B cells secrete antibodies
and T cells develop antigen receptors.
There are two types of immune responses, both triggered by antigens:
Antibody-mediated immune response (cells attack cells)
B-cells change into plasma cells, which synthesise and secrete proteins called
antibodies. These antibodies are released into the lymph and blood systems and
bind to and inactivate the antigen. The antigen is then destroyed. This type of
immunity works mainly against antigens present in body fluids and extracellular
pathogens that multiply in body fluids but rarely enter body cells (primarily bacteria).
Cell-mediated immune response (antibodies attack cells)
Certain T cells proliferate into cytotoxic T cells, which directly attack the invading
antigen. CD8+ T cells become ‘ killer cells ‘ and will specifically target intracellular
pathogens i.e. ones that reside in host cells - primarily viruses, parasites and fungi,
some cancer cells and sometimes foreign tissue or organ transplants.
Mixed – Antibody-mediated and cell-mediated immune response
A given pathogen can provoke both types of immune responses. CD4+ T cells
become ‘helper’ cells that come to the aid of both the above-mentioned responses.
Antigens
An antigen causes the body to produce specific antibodies and / or specific T cells
that react with it. Antigens will stimulate the formation of specific antibodies and will
react specifically with the produced antibodies.
An entire microbe, such as a bacterium or virus may act as an antigen. Toxins
secreted by bacteria are also highly antigenic. Non microbial examples of antigens
include foods, pollen, drugs, cancer cells and serum from insects and humans.
The plasma membrane surface of most body cells contain what are called ‘selfantigens’. Their function is to help T cells recognise that an antigen is foreign and
not a ‘self’. This recognition is the first important stage in any immune response.
The body’s own molecules, recognised as ‘self’ do not normally act as antigens.
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Sometimes, however, the distinction between self and nonself antigens breaks
down, leading to an auto immune disease where the immune system attacks and
starts to destroy its own body tissues.
Antibodies
An antibody is a protein produced by plasma cells. These proteins have special
receptors which allow them to bind to foreign substances known as antigens. The
portion of the antibody that identifies and neutralises the antigen so that it cannot
affect the host organism is called an antigen-binding site.
Antibodies belong to a group of plasma proteins called globulins – this is why they
are also known as immunoglobulins or Igs. Immunoglobulins are grouped in five
different classes:
The five types of antibodies are:
Type of Antibody
Function
IgA
This is found in breast milk and saliva, and prevents
antigens crossing epithelial membranes and invading
deeper tissues.
IgD
This is made by B-cells and displayed on their surfaces.
Antigens bind here to activate B-cells.
IgE
These are found on cell membranes of basophils and mast
cells. If it binds its antigen, this activates the inflammatory
response. It is often found in abundance in allergy.
IgG
This is the largest and most common antibody. It attacks
many different pathogens and crosses the placenta to
protect the foetus.
IgM
This is produced in great quantities in the primary
response.
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ALLERGY TRIGGERS and the BODY’S RESPONSE
The immune system works to protect us from many micro-organisms, some of which
cause infectious diseases. An allergy is an overaggressive response by the body’s
immune system to a substance that, for many people, is usually harmless. While
food remains the most common cause, there are many other substances, known as
allergens, that can cause a reaction - for example:
 plants
 animal fur
 feathers
 chemicals - paint
 plasters
 medicines - penicillin
 bee & wasp stings
Allergens may be inhaled or swallowed, or they may come into direct contact with
the eyes or skin. The antibodies that are produced to attack the allergen also lead
to a release of various substances including histamine. Histamine is responsible for
causing most of the allergy symptoms. So, it is not the allergens that cause allergy
symptoms but the way in which the body’s immune system reacts to them. Most
people do not produce an excessive reaction when exposed to dust or pollen, but
some people’s bodies overreact by producing lots of histamine and other substances
that create the common allergy symptoms such as; hayfever, rhinitis (running nose),
coeliac disease, asthma, eczema, sneezing, migraine, urticaria (itching) and watery
eyes.
It is likely that around 15% of the population is allergic to some fluids - shellfish is
one of the commonest and most dramatic, with rashes, asthmatic attacks, swollen
lips and eyes, stomach cramps, vomiting and constriction of the throat occurring in
seconds. This type of reaction is called anaphylactic shock and is caused by a
breakdown of the body’s immune defence mechanisms, which protect against
invading organisms. Sometimes the antibodies produced by the immune system
react violently to certain foods causing ‘ classic ‘ allergy reactions. These foods can
be easily identified and avoided.
Some individuals are affected by ‘masked’ allergies i.e. they do not produce
symptoms which are typically linked to allergies, such as spots or rashes, but they
nevertheless undermine health in a more subtle way. The substances which cause
these masked allergies are usually ones that we come into contact with on a daily
basis. Once the substance is removed, tremendous improvements in health and
well-being are noticed.
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STAGES OF INFECTION
Infection occurs when germs enter into the tissues, survive, grow and multiply.
ENTRY OF GERMS - Pathogens are organisms that can invade the body and cause
disease. They attack the body’s cells, or release powerful poisons called
toxins. Nearly all pathogens are microscopic living things, called micro-organisms.
The most important pathogens are bacteria and viruses.
INFECTION - If a micro-organism breaks through the body’s defences, it may grow
and reproduce very quickly inside the body. The result is infection. Unless the
infection is rapidly dealt with, it will cause an infectious disease.
INCUBATION PERIOD - After a pathogen successfully invades the body, some time
passes before a disease develops. This interval is known as the incubation period.
Some pathogens have an incubation period of a few hours or days, other are
between one and a number of years. The pathogen may be passed on to other
people during this time.
INFECTIOUS STAGE - This is the time during which the germs of the infectious
disease can spread. The person can be infectious during the incubation period,
during the illness itself, and sometimes after it (as a carrier).
CONVALESCENCE - The symptoms disappear and the patient regains strength.
SYMPTOMS & SIGNS OF INFECTIOUS DISEASE Fever / chills
Dark,yellow urine
Hot, dry skin
Dehydration / Thirst
Sweating
Headache
Furred tongue
ORGANISMS THAT CAUSE INFECTION
Understanding infection vs. disease
There is a distinct difference between infection and disease. Infection, often the first
step, occurs when bacteria, viruses or other microbes enter the body and begin to
multiply. Disease occurs when the cells in the body are damaged — as a result of
the infection — and signs and symptoms of an illness appear.
In response to infection, the immune system springs into action. An army of white
blood cells, antibodies and other mechanisms goes to work to rid the body of
whatever is causing the infection. For instance, in fighting off the common cold, the
body might react with fever, coughing and sneezing.
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Infectious agents come in a variety of shapes and sizes. Categories include:
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Bacteria
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Viruses
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Fungi
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Parasites - (protozoa and helminths)
BACTERIA
Bacteria are one-celled micro-organisms. They are very small. They are shaped like
short rods, spheres or spirals.
Not all bacteria are harmful. In fact, less than 1% cause disease, and some bacteria
that live in the body are actually beneficial. For instance, Lactobacillus acidophilus —
a harmless bacterium that resides in the intestines — helps to digest food, destroys
some disease-causing organisms and provides nutrients to the body.
Harmful bacteria will gain access to host tissue and will multiply. They do this by
penetrating the skin, mucous membranes or intestinal epithelium or surfaces that
normally act as a microbial barrier. Entry is also gained through open wounds.
Bacteria cling to specific cells on the mucous membranes of the respiratory,
digestive or genitourinary tracts allowing the bacteria to invade and multiply. The
organisms often remain localised producing a small infection e.g. a boil, carbuncle or
pimple. Or they may gain access to distant sites and this can happen via the
lymphatic system where the bacteria is deposited in the lymph nodes. Or if it enters
the blood stream it can end up in the liver or spleen. The spread of bacteria
throughout the body via blood or lymph can result in systemic infection of the body.
Many disease-causing bacteria produce toxins — powerful chemicals that damage
cells and cause illness. Bacteria cause diseases such as:
 Strep throat is a bacterial throat infection that can make the throat feel sore and
scratchy. Most sore throats are caused by viruses and usually go away on their own.
Only a small portion of sore throats are the result of strep throat. It's important to
identify strep throat for a number of reasons. If untreated, strep throat can
sometimes cause complications such as kidney inflammation and rheumatic fever.
Rheumatic fever can lead to painful and inflamed joints, a rash and even damage to
heart valves.
 Tuberculosis (TB) is a potentially serious infectious disease that primarily
affects the lungs. Tuberculosis is spread from person to person through tiny droplets
released into the air. Most people who become infected with the bacteria that cause
tuberculosis don't develop symptoms of the disease.
 Cellulitis is a common, potentially serious bacterial skin infection. Cellulitis
appears as a swollen, red area of skin that feels hot and tender, and it may spread
rapidly. Cellulitis may affect only the skin's surface — or, cellulitis may also affect
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tissues underlying the skin and can spread to the lymph nodes and bloodstream.
Left untreated, the spreading infection may rapidly turn life-threatening.
VIRUSES
Viruses are much smaller than cells. Viruses are capsules that contain genetic
material. They may be shaped like rods, spheres or tiny tadpoles. Viruses replicate
by invading and infecting the cells of living hosts. The newly made viruses then leave
the host cell, sometimes killing it in the process, and then seek out other cells within
the host to infect. A virus is not a cell and it doesn’t have any cellular parts. Because
viruses invade cells, no drugs have been found yet, that can kill viruses. The only
defence against a viral disease at the moment is the human immune system.
Viruses are responsible for causing a wide range of diseases, including:

AIDS is a chronic, life-threatening condition caused by the human
immunodeficiency virus (HIV). By damaging the immune system, HIV
interferes with the body's ability to fight off viruses, bacteria and fungi that
cause disease. HIV makes people more susceptible to certain types of
cancers and to infections the body would normally resist, such as pneumonia
and meningitis. The virus and the infection itself are known as HIV. "Acquired
immunodeficiency syndrome (AIDS)" is the name given to the later stages of
an HIV infection.
 Common cold is a viral infection that causes inflammation of the mucous
membranes lining the nose and throat, resulting in a stuffy, runny nose and
sometimes also a sore throat, headache and other discomfort. Most colds
are contracted by breathing in virus-containing droplets that have either been
sneezed or coughed into the atmosphere.
 Genital herpes is a common sexually transmitted disease that affects both
men and women. Features of genital herpes include pain, itching and sores in
your genital area. The cause of genital herpes is a type of herpes simplex
virus (HSV), which enters the body through small breaks in the skin or
mucous membranes. Sexual contact is the primary way that the virus
spreads.
 Influenza is a viral infection that attacks the respiratory system, including the
nose, throat, bronchial tubes and lungs. People who are generally healthy
and who catch influenza — commonly called the flu — are likely to feel rotten
for a few days, but probably won't develop complications or need hospital
care. If they have a weakened immune system or chronic illness, though,
influenza can be fatal.
 Measles is a potentailly dangerous viral illness that causes a characteristic
rash and a fever. It is highly infective and is spread primarily by airborne
droplets of nasal secretions. Measles mainly affects children but can occur at
any age.
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 Yellow Fever Yellow fever is a haemorrhagic fever caused by a virus spread
by a particular species of mosquito. It's most common in areas of Africa and
South America, affecting travellers to and residents of those areas. In mild
cases, yellow fever causes fever, headache, nausea and vomiting. But yellow
fever can become more serious, causing bleeding (haemorrhaging), heart,
liver and kidney problems. Up to 50 percent of people with the more severe
form of yellow fever die of the disease.
 Plantar warts are non cancerous skin growths found on the soles of the feet,
caused by the human papillomavirus (HPV), which enters the body through
tiny cuts and breaks in the skin. This virus causes a rapid growth of cells on
the outer layer of the skin. Plantar warts often develop beneath pressure
points in the feet, such as the heels or balls of the feet.
 Common warts usually grow on the hands or fingers. They are as above treatment helps to prevent them from spreading to other parts of the body or
to other people.
Antibiotics have no effect on viruses.
FUNGI
There are many different varieties of fungi, and we eat quite a few of them.
Mushrooms are fungi, as is the mould that forms the blue or green veins in some
types of cheese. And yeast, another type of fungi, is a necessary ingredient to make
most types of bread
Other fungi can cause illness. One example is candida — a yeast that can cause
infection. Candida can cause thrush — an infection of the mouth and throat — in
infants and in people taking antibiotics or who have an impaired immune system.
Fungal diseases are called mycoses and those affecting humans can be divided into
four groups based on the level of penetration into the body tissues:
1. Superficial mycoses are caused by fungi that grow only on the surface of
the skin or hair. This type of fungus lives off keratin which is found in
abundance on skin, hair and nails.
2. Cutaneous mycoses or dermatomycoses include such infections as
athlete's foot and ringworm. This type of fungus combines with bacteria to
cause soggy and itching skin between the toes.
3. Subcutaneous mycoses penetrate below the
subcutaneous, connective, and bone tissue.
skin
to
involve
the
4. Systemic or deep mycoses are able to infect internal organs and become
widely disseminated throughout the body. This type is often fatal.
Oral thrush is a condition in which the fungus Candida albicans accumulates on the
lining of the mouth. Oral thrush causes creamy white lesions, usually on the tongue
or inner cheeks. The lesions can be painful and may bleed slightly when scraped.
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Sometimes oral thrush may spread to the roof of the mouth, gums, tonsils or the
back of the throat.
Fungi are also responsible for such skin problems as athlete's foot and ringworm.
Athlete's foot is a fungal infection that develops in the moist areas between the toes
and sometimes on other parts of the foot. Athlete's foot usually causes itching,
stinging and burning.
Also called tinea pedis, athlete's foot is closely related to other fungal infections
with similar names, which include:

Ringworm of the body (tinea corporis). This form causes a red, scaly ring
or circle of rash on the top layer of your skin.

Jock itch (tinea cruris). This form affects your genitals, inner upper thighs
and buttocks.

Ringworm of the scalp (tinea capitis). This form is most common in
children and involves red, itchy patches on the scalp, leaving bald patches.
PARASITES
Parasites may be protozoa or multi-cellular organisms that behave like tiny animals
— hunting and gathering other microbes for food. Many protozoa reside in the
intestinal tract and are harmless.
Protozoa often spend part of their life cycle outside of humans or other hosts, living
in food, soil, water or insects. Some protozoa invade the body through the food we
eat or the water we drink. Others, such as malaria, are transmitted by mosquitoes.
Others cause disease, such as:
 Giardia infection is an intestinal infection marked by abdominal cramps,
bloating, nausea and watery diarrhoea. Giardia infection is caused by a
parasite that is found worldwide, especially in areas with poor sanitation and
unsafe water. Giardia infection (giardiasis) is one of the most common
waterborne diseases in the United States. The parasites are found in
backcountry streams and lakes, but also in municipal water supplies,
swimming pools and spas. Giardia infection can also be transmitted through
food and person-to-person contact.
 Malaria is an infectious disease caused by a parasite that's transmitted by
mosquitoes. The illness results in recurrent attacks of chills and fever, and it
can be deadly.
 Toxoplasmosis is a parasitic infection that may cause flu-like symptoms. The
organism that causes toxoplasmosis — Toxoplasma gondii — is one of the
world's most common parasites. Most people affected never develop signs
and symptoms. But for infants born to infected mothers and for people with
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compromised immune systems, toxoplasmosis can cause extremely serious
complications.
HELMINTHS
Helminths are among the larger parasites. The word "helminth" comes from the
Greek for "worm." If this parasite — or its eggs — enters the body, it takes up
residence in the intestinal tract, lungs, liver, skin or brain, where it lives off the
nutrients in the body. They cannot produce food or energy for themselves. They are
harmful to humans because the consume needed food, eat away body tissue and
cells, eliminating toxic waste, which makes people sick. The most common
helminths are tapeworms and roundworms.
Tapeworm infection is caused by ingesting food or water contaminated with
tapeworm eggs or larvae. If certain tapeworm eggs are ingested, they can migrate
outside the intestines and form cysts in body tissues and organs (invasive tapeworm
infection). If tapeworm larvae are ingested, however, they develop into adult
tapeworms in the intestines (intestinal tapeworm infection).
An adult tapeworm consists of a head, neck and chain of segments called
proglottids. If an intestinal tapeworm infection is present, the tapeworm head
adheres to the intestine wall, and the proglottids grow and produce eggs. Adult
tapeworms can live for up to 20 years in a host. Intestinal tapeworm infections are
usually mild, but invasive tapeworm infections can cause serious complications.
Trichinosis sometimes called trichinellosis, is a type of roundworm infection.
Roundworms are parasites that use a host body to stay alive and reproduce.
Trichinosis occurs primarily among meat-eating animals (carnivores), especially
bears, foxes and walruses. Trichinosis infection is acquired by eating larvae in meat.
When humans eat undercooked meat containing trichinella larvae, the larvae mature
into adult worms in the intestine over several weeks. The adults then produce larvae
that migrate through various tissues, including muscle.
Ascariasis is a type of roundworm infection. Roundworms are parasites that use the
body as a host to stay alive and reproduce, maturing from eggs to adult worms
inside your body. Eggs of the ascaris roundworm are microscopic, but adult worms
are the largest of the intestinal roundworms, reaching lengths up to 16 inches (41
centimeters).
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THE INFLAMMATORY PROCESS
Inflammation is the body’s response to tissue damage. It represents a protective
response designed to rid the body of the initial cause of tissue damage and the
consequences of that injury.
Tissue damage may occur due to: trauma, physical and chemical agents, foreign
bodies, immune reactions and infections.
Inflammation occurs locally and can be:

Acute - rapid onset and of short duration

Chronic - prolonged duration and results in tissue necrosis
The purpose of the inflammatory process within the body is to isolate, then
inactivate, then remove the cause of the damaged tissue and the damaged tissue
itself.
What happens to protect the integrity of the body when the tissue is damaged?
1. Tissue is made up of millions of cells (cells make tissue, tissue make organs,
organs makes systems). Cells, when they are damaged release histamine
and serotonin from their cell walls. This sets off a chain reaction, firstly
causing dilation of tiny capillaries because histamine stimulates the dilation of
blood capillary walls. More blood flows to the site of the damage and this
causes warmth in the area and reddening.
2. Because the capillary walls have dilated, tissue fluid within the cell is
stimulated to increase in volume. But the cell walls are broken at the site of
the tissue damage, so tissue fluid normally held within the cell structure oozes
out of the damaged cell through its leaky walls into the spaces between the
cells (interstitial spaces). This is called oedema. This is also how the site of
the tissue damage becomes isolated, because the area swells due to the
amount of tissue fluid leaking into the interstitial spaces.
3. Because histamine is present in the blood, and antigens are circulating in the
blood due to damage in the tissues, leucocytes migrate to the damaged area
to mop up the antigens (phagocytosis) and render them inactive.
4. Macrophages then are stimulated to the area because of the changes in
blood constituents (histamine, leucocyte proliferation) and mop up dead
tissue that has been left over. This provides the removal part of the chain of
events.
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Signs to look for when the inflammatory process is happening in the body: redness,
heat, pain, swelling, and occasionally, loss of function.
CELLS INVOLVED IN THE INFLAMMATORY PROCESS
NERVE CELLS
These are elongated cells that transmit information rapidly between different parts of
the body.
MAST CELLS
These are part of a group of cells called leucocytes. Leucocytes are white blood
cells and are found in blood plasma.
They are found in most tissues
characteristically surrounding blood vessels and nerves. They play a key, protective
role in the inflammatory process. They are rich in histamine and heparin.

Heparin - prevents blood from clotting to allow blood to flow to the area of
infection or injury.

Histamine - dilates the blood capillary walls, causing tissue fluid to ooze from
damaged cell walls - swelling (oedema). It also initiates nerve endings
(leading to itching and pain). Think of the bump and redness and itching after
a mosquito bite.
MONOCYTES
These are a type of leucocyte (or white blood cell). Low monocyte count is a good
sign, high count indicates that a problem is present.
MACROPHAGES
These are a type of white blood cell that eats foreign material / debris, bacteria,
viruses in the body. They are part of the innate immune response and also make up
an important part of the body’s acquired immune system.
NEUTROPHILS
These are the most common type of white blood cell, comprising about 50 - 70% of
all white blood cells. They are phagocytic (can ingest other cells) and are the first
immune cells to arrive at a site of infection.
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