THE BLUE FOOTED BOOBY
IMMUNE SYSTEM- The
primary role of the immune system is to provide the bird with the ability to
resist invasion and injurious effects from pathogens (disease causing
organisms.) A bird’s immune system consists mainly of lymphatic vessels and
lymphoid tissues.
Major Lymph Organs
The two major immune system organs are: bursa of Fabricius (associated
with B-cells and the Thymus Gland (associated with T-cells).Bursa
of Fabricius is predominate in young birds and is situated adjacent to the cloaca. It is the
source of antigen-producing B-lymphocytes in
embryonic stage. B-lymphocytes, the cells that produce antibodies, are
initially produced in the embryonic liver, yolk sac and bone marrow, then move
through the blood to the bursa of Fabricius where they mature. Gradually, as
birds grow older, the bursa of Fabricus becomes smaller. At about the time of
the bird's sexual maturity, it has atrophied and no longer functions.
The thymus gland
is located in the neck along the jugular vein and functions at peak levels in
the young. It produces hormones that program certain lymphocytes against certain
antigens. T-lymphocytes begin as the same stem cells as the B-cells, but are
programmed in the thymus rather than the bursa of Fabricus.
The spleen is divided into red and white pulp. The white pulp is where the
T-lymphocytes reside. The spleen filters and cleans the blood of debris and destroys worn out
red blood cells. The bone marrow produces lymphocytes and macrophages. The lymph
nodes filter lymph.
Secondary Lymph Organs
The secondary lymphatic organs are the spleen, bone marrow, mural lymph nodules and
lymph nodes along with the lymphatic circulatory system of vessels and
capillaries that transport lymph fluid throughout the body. Unlike mammals,
birds do not have organized lymph nodes.
The immune system is divided into non-specific and specific immune mechanisms and
has three types of defenses. The first two defenses are considered non-specific
while the third is specific.
The non-specific defense system responds immediately to protect the bird from all
foreign substances. They are provided by intact skin, mucous membranes, the
inflammatory response, white blood cells, and a number of proteins produced by
body cells. This system reduces the workload of the specific defense system by
preventing entry and spread of microorganisms throughout the body.
The specific defense system puts up an attack against particular foreign substances.
While certain body organs are involved, the immune response consists mostly of a
variety of molecules and immune cells (lymphocytes and macrophages), which
inhibit the lymphatic tissues and circulate in body fluids.
When the immune system is functioning properly, it will protect against most invading
bacteria, viruses, and cell that have turned on its own body. It does this by
cell attack and by releasing mobilizing chemicals and protective antibody
molecules.
First Defense
The first defense is the feathers and skin, which provide a physical barrier that
some disease organisms cannot penetrate. Another is the normal microflora found
in the stomach along with a thick mucus layer. When the population of microbial
is dense and stable in the stomach, mucus helps to prevent the invading
organisms from gaining a foothold. In the respiratory tract there are fine
hair-like projections called cilia that help to sweep invading bacteria back up
toward the beak keeping it from entering the lower respiratory system. When the
first defense if penetrated and the pathogens invade deeper tissues the second
line of defense comes to defend the body.
Second Defense
The second line of defense is made up of cells and a chemical defense. These are
circulating in the blood and into organs. Phagocytes are large white cells that
attract the pathogen and engulf it and digest it. Phagocytes include monocytes,
macrophages, and neutrophils.
Monocytes
circulate in the blood and travel to the site of infection. Once at the site
they turn into a macrophages. Macrophages are found in tissues throughout the
body. They act as scavengers, secrete a wide variety of powerful chemicals, and
they play a role in activating T cells. Neutrophils form a primary defense
against bacteria and move out of the blood to infected tissue when needed. In a
serious bacteria infection, neutrophils will be produced in increased numbers
resulting in a higher than normal white blood count.
Natural
killer cells (NK) patrol the body in the lymph and blood. They attack the
membrane of target cell and release chemicals that cause the target cell’s
membrane and nucleus to disintegrate. They kill cancer cells, tumor cells and
virus-infected cells before the specific immune system gets involved. Natural
killer cells can act upon any target cell by recognizing certain sugars on the
invading cell’s surface.
The
inflammatory response begins with a chemical alarm. When cells are injured they
release inflammatory chemicals such as, histamines and kinins that activate pain
receptors, cause blood vessels and capillaries to become dilated and leaky
(causing heat, redness and swelling) and attract phagocytes and white blood
cells to the area. The inflammatory response prevents the spread of damaging
agents to nearby tissues, sends the phagocytes to dispose of cell debris and
pathogens, sends clotting proteins to the area, and sets the stage for
repair.
Antimicrobial
chemicals are another defense. These include, interferons, complements (20+
plasma proteins that circulate in the blood inactive until they attach to a
foreign cell) and fever. Interferons are proteins released by virus-infected
cells that protect uninfected tissue cells from a viral takeover. Complements
breakdown microorganisms and help to intensify the inflammatory response. Fever
inhibits multiplication of bacteria and enhances the body repair process.
The
Immune System
(specific defense)
The
immune response immensely increases the inflammatory response and provides
protection that is carefully targeted against specific antigens. Once it has
been exposed to a new antigen it will store it in it’s memory bank and react to
it more intensely the next time around.
Antigen
An
antigen is any substance that gets the immune system excited so that it induces
a response. Antigens can be foreign proteins, large carbohydrates, pollen,
bacteria, fungi, virus particles, and some lipids. Antigens are usually large
molecules, but small molecules may link up with the body’s own proteins and seem
foreign to the immune system, therefore triggering an immune response (like
allergies).
Cells
of the Immune System
The major cells of the immune system are lymphocytes and macrophages. There are two types of lymphocytes, B-lymphocytes, and T-lymphocytes created in the embryonic liver, yolk sac, and bone marrow. The T-cells travel to the thymus to become capable to responding to specific antigens by binding to them. B-cells travel to the bursa of Fabricius (for approximately 6 weeks) where they get programmed for their specific antigen. Once capable, they circulate in the blood and lymph and travel to the other lymph organs where they encounter antigens. Once they have recognized and bound to an antigen they become mature lymphocytes and only attack that certain antigen.
B-cells
produce antibodies. Antibodies are soluble proteins made up of amino acids. They
inactivate antigens by binding to the antigen, breaking down the cell wall and
release molecules that enhance the inflammatory process. Antibodies can bind to
more than one antigen at a time. This process produces clumping and
immobilization, which allows the phagocytes to capture and engulf the antigens
more easily.
There
are three classes of antibodies, known as immunoglobulins (Ig), produced in
birds after exposure to a disease organism: IgM, IgG, and IgA. IgM appears after
4-5 days following exposure to a disease organism and then disappears by 10-12
days. IgG is detected after 5 days following exposure, peaks at 3 to 3 1/2
weeks, and then slowly decreases. IgA appears after 5 days following exposure.
This antibody is found primarily in the mucus secretions of the eyes, gut, and
respiratory tract.
T-cells
are not able to bind to free antigens. Instead, macrophages engulf antigens and
present them on its membrane for recognition by the T cell bearing the same
receptor for the same antigen. Macrophages also release a chemical that
activates the T cells. Killer T cells bind to an antigen inserting a chemical
called perforin into the foreign cell’s membrane that causes it to rupture.
Helper T cells circulate through the body and recruit other cells to fight the
antigens. Suppressor T cells slow down the body’s immune system when an antigen
has been successfully inactivated or destroyed.
Protective
Nutrients
While
the immune system is responding against pathogens, it too can produce harmful
substances. When the immune system acts, T-cells, B-cells and phagocytes are
multiplying rapidly and are prone to peroxidative damage by free radicals.
Certain antioxidants may help. Vitamin E is present in the cellular membranes
and prevents oxidation of unsaturated lipids by free radicals. Vitamin E works
closely with Selenium, which is a component of an enzyme (glutathione
peroxidase) that removes active peroxides from cells before they oxidize
unsaturated lipids. Vitamins C and A are both antioxidants. Vitamin C can
inactivated free radicals directly in the cell and can act indirectly by
regenerating the antioxidant form of Vitamin E.
Zinc
is a cofactor for the antioxidant enzyme superoxide dismutase. Zinc plays a role
in cell division, cell stability, protein metabolism, and carbohydrate
digestion. It aids in wound healing and lymphocyte productions. Deficiency can
reduce the number or T cells and decrease natural killer cell activity. Copper
enhance the development of red and white blood cells. Deficiency reduces the
maturation of lymphocytes. Magnesium is crucial for lymphocyte growth.
Deficiency reduces the levels of immunoglobulin and antibody forming cells and
promotes production of free radicals and lipid
peroxidation.
Some
Herbs for the Immune System
Astragalus
Astragalus
promotes healing and strengthens the immune system and is often used as a
preventative at the onset of infection. It has been found to enhance the immune
system by stimulating the responsiveness of T-cells. Research at the University
of Texas took damaged immune cells from cancer patients and added Astragalus
extract to the cells and compared them to normal immune cells. The Astragalus
was able to completely restore the cancer patient’s cells to normal and in some
instances the cells were stimulated to a more heightened response than that of a
normal cells. Another study suggested long-term use (35 days) heightened the
activity of spleen cells.
Echinacea
Echinacea
helps to activate macrophages that are directly involved with the destruction of
infectious agents. It also increases the production of interferon (a protein
released by virus-infected cells that protect uninfected tissue cells from viral
takeover), an important part of the body’s defense against viral infections. It
has also been shown to activate natural killer T cells and is an
anti-inflammatory. It also inhibits the bacterial enzyme hyaluronidase, to help
prevent bacterial access to healthy cells.
Garlic
Garlic
is rich in antioxidants, vitamins, and minerals. Helps to enhance phagocyte
activity and proliferation of T cells and the sulfur compounds enhance natural
killer cells. It has antibacterial, antiviral, and antifungal activity. It has
been shown to inhibit the growth of the yeast organism Candidiasis
albicans.
Reishi
Mushroom
Reishi
mushroom has adaptogenic qualities that normalize bodily functions and improve
stamina. It is an antioxidant that raises T-cell levels and inhibits bacteria
and viruses.
ENDOCRINE SYSTEM-
The endocrine system consists of a number of organs (glands)
located in different areas of the body which play an important part in the
proper functioning of the animal. The organs produce special compounds called
hormones, which, in turn, target particular systems or organs, and the way that
they function. These glands are called endocrine glands because they do not have
an opening to discharge their secretions but discharge them directly into the
blood stream. They are then carried to their target systems and organs to carry
out their task. In many cases different hormones operating together regulate
particular functions. When these get out of balance, the bird’s body cannot
function properly and hence performance will suffer, in some cases even to
death. Pituitary gland or hypothesis The
pituitary gland is often called the master gland because many of the compounds
it produces target other similar glands to trigger them to produce their
compounds that, in turn, influence the functioning of a particular system or
organ. Thus, it can be said it is a controlling gland.
The pituitary gland is a pea-sized gland located at the base of the brain and is well protected by
the surrounding skull bones. It consists of two
parts:
The
anterior pituitary gland is stimulated by special releasing factors from the
hypothalamus of the brain to produce and release a number of chemical compounds.
These compounds are hormones and
include:
The amount of these hormones produced by the pituitary gland will influence the level of
activity of the target organ or response. The more that is produced the greater
will be the response. The posterior pituitary gland produces arginine
vasotocin and stores oxytocin that is produced by the
hypothalamus. These play a part in the release of the yolk into
the oviduct and the actual laying of the egg or oviposition. The secretions
produced or stored in the pituitary gland enter the blood stream and are then
transported to the part of the body that they
target.
Hypothalamus
The hypothalamus is a major part of the brain located at its base and more or less
centrally in the skull. As far as its endocrine functions are concerned, they
include the production of the releasing factors that act as a control on the
anterior pituitary gland, and oxytocin that plays a part in the
release of the yolk. The quantity of the releasing factors and oxytocin released
is influenced by day length – the longer the day to 18 hours the greater the
amount of these compounds released and the greater the effect on the target
gland or function.
Adrenal gland
The adrenal glands are small glands approximately 9 mm long located anterior to or in front
of the kidneys. There are two such glands, each associated with a particular
kidney. Each gland consists of two different types of cells that form two
distinct parts of the gland – the adrenal cortex and the adrenal
medulla.
The cortex
produces three hormones:
The adrenal
medulla produces two compounds:
Thyroid
gland
The thyroid
gland consists of two reddish purple glands lying one on each side of the base
of the neck. This gland produces two
hormones:
Parathyroid
glands
These are
two small, round, yellowish-white glands located at the base of the thyroid
glands at the base of the neck. They produce a hormone called parathormone.
Parathormone reacts to low blood calcium levels and works to increase the amount
of calcium in the blood.
Ultimobranchial
bodies
These are
1-3 mm long and are located just posterior (behind) to the parathyroid glands.
They produce a hormone called calcitonin that works to reduce the calcium level
in the blood stream. Thus, the hormones parathormone of the parathyroids and
calcitonin of the ultimobranchial bodies must be in balance if the calcium
levels in the blood are to be in balance to
requirements.
Pineal body
The pineal
body is a very small gland located above the mid-brain. Using tryptophan (an
amino acid) it produces melatonin. Melatonin affects sleep, behaviour and brain
electrical activity. Thus the pineal body acts as a biological clock and as such
has an effect on the activities of the hypothalamus and its production of
releasing factors.
Islets of
langerhans
These are
small clumps of special cells located in the pancreas, which sits in the
duodenal loop of the small intestine. These special cells produce two
hormones:
Gonads
The sex
organs of males and females are called the gonads. These organs produce hormones
called sex hormones and include:
males and females produce and need all three hormones but in different amounts.
When a male is castrated, for example, the balance of the sex hormones is
affected, leading to the bird taking on female characteristics. This means that
a capon or castrated male will, over time, take on much of the appearance and
behavior of a female.
IMMUNE SYSTEM- The
primary role of the immune system is to provide the bird with the ability to
resist invasion and injurious effects from pathogens (disease causing
organisms.) A bird’s immune system consists mainly of lymphatic vessels and
lymphoid tissues.
Major Lymph Organs
The two major immune system organs are: bursa of Fabricius (associated
with B-cells and the Thymus Gland (associated with T-cells).Bursa
of Fabricius is predominate in young birds and is situated adjacent to the cloaca. It is the
source of antigen-producing B-lymphocytes in
embryonic stage. B-lymphocytes, the cells that produce antibodies, are
initially produced in the embryonic liver, yolk sac and bone marrow, then move
through the blood to the bursa of Fabricius where they mature. Gradually, as
birds grow older, the bursa of Fabricus becomes smaller. At about the time of
the bird's sexual maturity, it has atrophied and no longer functions.
The thymus gland
is located in the neck along the jugular vein and functions at peak levels in
the young. It produces hormones that program certain lymphocytes against certain
antigens. T-lymphocytes begin as the same stem cells as the B-cells, but are
programmed in the thymus rather than the bursa of Fabricus.
The spleen is divided into red and white pulp. The white pulp is where the
T-lymphocytes reside. The spleen filters and cleans the blood of debris and destroys worn out
red blood cells. The bone marrow produces lymphocytes and macrophages. The lymph
nodes filter lymph.
Secondary Lymph Organs
The secondary lymphatic organs are the spleen, bone marrow, mural lymph nodules and
lymph nodes along with the lymphatic circulatory system of vessels and
capillaries that transport lymph fluid throughout the body. Unlike mammals,
birds do not have organized lymph nodes.
The immune system is divided into non-specific and specific immune mechanisms and
has three types of defenses. The first two defenses are considered non-specific
while the third is specific.
The non-specific defense system responds immediately to protect the bird from all
foreign substances. They are provided by intact skin, mucous membranes, the
inflammatory response, white blood cells, and a number of proteins produced by
body cells. This system reduces the workload of the specific defense system by
preventing entry and spread of microorganisms throughout the body.
The specific defense system puts up an attack against particular foreign substances.
While certain body organs are involved, the immune response consists mostly of a
variety of molecules and immune cells (lymphocytes and macrophages), which
inhibit the lymphatic tissues and circulate in body fluids.
When the immune system is functioning properly, it will protect against most invading
bacteria, viruses, and cell that have turned on its own body. It does this by
cell attack and by releasing mobilizing chemicals and protective antibody
molecules.
First Defense
The first defense is the feathers and skin, which provide a physical barrier that
some disease organisms cannot penetrate. Another is the normal microflora found
in the stomach along with a thick mucus layer. When the population of microbial
is dense and stable in the stomach, mucus helps to prevent the invading
organisms from gaining a foothold. In the respiratory tract there are fine
hair-like projections called cilia that help to sweep invading bacteria back up
toward the beak keeping it from entering the lower respiratory system. When the
first defense if penetrated and the pathogens invade deeper tissues the second
line of defense comes to defend the body.
Second Defense
The second line of defense is made up of cells and a chemical defense. These are
circulating in the blood and into organs. Phagocytes are large white cells that
attract the pathogen and engulf it and digest it. Phagocytes include monocytes,
macrophages, and neutrophils.
Monocytes
circulate in the blood and travel to the site of infection. Once at the site
they turn into a macrophages. Macrophages are found in tissues throughout the
body. They act as scavengers, secrete a wide variety of powerful chemicals, and
they play a role in activating T cells. Neutrophils form a primary defense
against bacteria and move out of the blood to infected tissue when needed. In a
serious bacteria infection, neutrophils will be produced in increased numbers
resulting in a higher than normal white blood count.
Natural
killer cells (NK) patrol the body in the lymph and blood. They attack the
membrane of target cell and release chemicals that cause the target cell’s
membrane and nucleus to disintegrate. They kill cancer cells, tumor cells and
virus-infected cells before the specific immune system gets involved. Natural
killer cells can act upon any target cell by recognizing certain sugars on the
invading cell’s surface.
The
inflammatory response begins with a chemical alarm. When cells are injured they
release inflammatory chemicals such as, histamines and kinins that activate pain
receptors, cause blood vessels and capillaries to become dilated and leaky
(causing heat, redness and swelling) and attract phagocytes and white blood
cells to the area. The inflammatory response prevents the spread of damaging
agents to nearby tissues, sends the phagocytes to dispose of cell debris and
pathogens, sends clotting proteins to the area, and sets the stage for
repair.
Antimicrobial
chemicals are another defense. These include, interferons, complements (20+
plasma proteins that circulate in the blood inactive until they attach to a
foreign cell) and fever. Interferons are proteins released by virus-infected
cells that protect uninfected tissue cells from a viral takeover. Complements
breakdown microorganisms and help to intensify the inflammatory response. Fever
inhibits multiplication of bacteria and enhances the body repair process.
The
Immune System
(specific defense)
The
immune response immensely increases the inflammatory response and provides
protection that is carefully targeted against specific antigens. Once it has
been exposed to a new antigen it will store it in it’s memory bank and react to
it more intensely the next time around.
Antigen
An
antigen is any substance that gets the immune system excited so that it induces
a response. Antigens can be foreign proteins, large carbohydrates, pollen,
bacteria, fungi, virus particles, and some lipids. Antigens are usually large
molecules, but small molecules may link up with the body’s own proteins and seem
foreign to the immune system, therefore triggering an immune response (like
allergies).
Cells
of the Immune System
The major cells of the immune system are lymphocytes and macrophages. There are two types of lymphocytes, B-lymphocytes, and T-lymphocytes created in the embryonic liver, yolk sac, and bone marrow. The T-cells travel to the thymus to become capable to responding to specific antigens by binding to them. B-cells travel to the bursa of Fabricius (for approximately 6 weeks) where they get programmed for their specific antigen. Once capable, they circulate in the blood and lymph and travel to the other lymph organs where they encounter antigens. Once they have recognized and bound to an antigen they become mature lymphocytes and only attack that certain antigen.
B-cells
produce antibodies. Antibodies are soluble proteins made up of amino acids. They
inactivate antigens by binding to the antigen, breaking down the cell wall and
release molecules that enhance the inflammatory process. Antibodies can bind to
more than one antigen at a time. This process produces clumping and
immobilization, which allows the phagocytes to capture and engulf the antigens
more easily.
There
are three classes of antibodies, known as immunoglobulins (Ig), produced in
birds after exposure to a disease organism: IgM, IgG, and IgA. IgM appears after
4-5 days following exposure to a disease organism and then disappears by 10-12
days. IgG is detected after 5 days following exposure, peaks at 3 to 3 1/2
weeks, and then slowly decreases. IgA appears after 5 days following exposure.
This antibody is found primarily in the mucus secretions of the eyes, gut, and
respiratory tract.
T-cells
are not able to bind to free antigens. Instead, macrophages engulf antigens and
present them on its membrane for recognition by the T cell bearing the same
receptor for the same antigen. Macrophages also release a chemical that
activates the T cells. Killer T cells bind to an antigen inserting a chemical
called perforin into the foreign cell’s membrane that causes it to rupture.
Helper T cells circulate through the body and recruit other cells to fight the
antigens. Suppressor T cells slow down the body’s immune system when an antigen
has been successfully inactivated or destroyed.
Protective
Nutrients
While
the immune system is responding against pathogens, it too can produce harmful
substances. When the immune system acts, T-cells, B-cells and phagocytes are
multiplying rapidly and are prone to peroxidative damage by free radicals.
Certain antioxidants may help. Vitamin E is present in the cellular membranes
and prevents oxidation of unsaturated lipids by free radicals. Vitamin E works
closely with Selenium, which is a component of an enzyme (glutathione
peroxidase) that removes active peroxides from cells before they oxidize
unsaturated lipids. Vitamins C and A are both antioxidants. Vitamin C can
inactivated free radicals directly in the cell and can act indirectly by
regenerating the antioxidant form of Vitamin E.
Zinc
is a cofactor for the antioxidant enzyme superoxide dismutase. Zinc plays a role
in cell division, cell stability, protein metabolism, and carbohydrate
digestion. It aids in wound healing and lymphocyte productions. Deficiency can
reduce the number or T cells and decrease natural killer cell activity. Copper
enhance the development of red and white blood cells. Deficiency reduces the
maturation of lymphocytes. Magnesium is crucial for lymphocyte growth.
Deficiency reduces the levels of immunoglobulin and antibody forming cells and
promotes production of free radicals and lipid
peroxidation.
Some
Herbs for the Immune System
Astragalus
Astragalus
promotes healing and strengthens the immune system and is often used as a
preventative at the onset of infection. It has been found to enhance the immune
system by stimulating the responsiveness of T-cells. Research at the University
of Texas took damaged immune cells from cancer patients and added Astragalus
extract to the cells and compared them to normal immune cells. The Astragalus
was able to completely restore the cancer patient’s cells to normal and in some
instances the cells were stimulated to a more heightened response than that of a
normal cells. Another study suggested long-term use (35 days) heightened the
activity of spleen cells.
Echinacea
Echinacea
helps to activate macrophages that are directly involved with the destruction of
infectious agents. It also increases the production of interferon (a protein
released by virus-infected cells that protect uninfected tissue cells from viral
takeover), an important part of the body’s defense against viral infections. It
has also been shown to activate natural killer T cells and is an
anti-inflammatory. It also inhibits the bacterial enzyme hyaluronidase, to help
prevent bacterial access to healthy cells.
Garlic
Garlic
is rich in antioxidants, vitamins, and minerals. Helps to enhance phagocyte
activity and proliferation of T cells and the sulfur compounds enhance natural
killer cells. It has antibacterial, antiviral, and antifungal activity. It has
been shown to inhibit the growth of the yeast organism Candidiasis
albicans.
Reishi
Mushroom
Reishi
mushroom has adaptogenic qualities that normalize bodily functions and improve
stamina. It is an antioxidant that raises T-cell levels and inhibits bacteria
and viruses.
ENDOCRINE SYSTEM-
The endocrine system consists of a number of organs (glands)
located in different areas of the body which play an important part in the
proper functioning of the animal. The organs produce special compounds called
hormones, which, in turn, target particular systems or organs, and the way that
they function. These glands are called endocrine glands because they do not have
an opening to discharge their secretions but discharge them directly into the
blood stream. They are then carried to their target systems and organs to carry
out their task. In many cases different hormones operating together regulate
particular functions. When these get out of balance, the bird’s body cannot
function properly and hence performance will suffer, in some cases even to
death. Pituitary gland or hypothesis The
pituitary gland is often called the master gland because many of the compounds
it produces target other similar glands to trigger them to produce their
compounds that, in turn, influence the functioning of a particular system or
organ. Thus, it can be said it is a controlling gland.
The pituitary gland is a pea-sized gland located at the base of the brain and is well protected by
the surrounding skull bones. It consists of two
parts:
- Anterior
pituitary - Posterior
pituitary
The
anterior pituitary gland is stimulated by special releasing factors from the
hypothalamus of the brain to produce and release a number of chemical compounds.
These compounds are hormones and
include:
- Thyroid Stimulating
Hormone – stimulates the thyroid
gland. - Adrenocorticotrophic
Hormone – stimulates the adrenal
cortex. - Sex hormones –
stimulates the sex glands: - Luteinising
Hormone - Follicle Stimulating
Hormone - Melanin Stimulating
Hormone – function in birds is
unknown. - Natural Growth
Hormone – stimulates growth of the
animal.
The amount of these hormones produced by the pituitary gland will influence the level of
activity of the target organ or response. The more that is produced the greater
will be the response. The posterior pituitary gland produces arginine
vasotocin and stores oxytocin that is produced by the
hypothalamus. These play a part in the release of the yolk into
the oviduct and the actual laying of the egg or oviposition. The secretions
produced or stored in the pituitary gland enter the blood stream and are then
transported to the part of the body that they
target.
Hypothalamus
The hypothalamus is a major part of the brain located at its base and more or less
centrally in the skull. As far as its endocrine functions are concerned, they
include the production of the releasing factors that act as a control on the
anterior pituitary gland, and oxytocin that plays a part in the
release of the yolk. The quantity of the releasing factors and oxytocin released
is influenced by day length – the longer the day to 18 hours the greater the
amount of these compounds released and the greater the effect on the target
gland or function.
Adrenal gland
The adrenal glands are small glands approximately 9 mm long located anterior to or in front
of the kidneys. There are two such glands, each associated with a particular
kidney. Each gland consists of two different types of cells that form two
distinct parts of the gland – the adrenal cortex and the adrenal
medulla.
The cortex
produces three hormones:
- Corticosterone –
carbohydrate and fat metabolism, breakdown of protein and important in the
bird’s reaction to stress - Aldosterone –
retention of sodium - 8-hydroxycorticosterone – function
unknown
The adrenal
medulla produces two compounds:
- Norepinephrine – fat
metabolism - Epinephrine –
control of blood pressure
Thyroid
gland
The thyroid
gland consists of two reddish purple glands lying one on each side of the base
of the neck. This gland produces two
hormones:
- Thyroxine – helps
regulate heat production, carbohydrate metabolism, promotes high blood sugar
level, and promotes growth - Triiodothyronine –
development of skin and feathers, may be involved in the moulting
process
Parathyroid
glands
These are
two small, round, yellowish-white glands located at the base of the thyroid
glands at the base of the neck. They produce a hormone called parathormone.
Parathormone reacts to low blood calcium levels and works to increase the amount
of calcium in the blood.
Ultimobranchial
bodies
These are
1-3 mm long and are located just posterior (behind) to the parathyroid glands.
They produce a hormone called calcitonin that works to reduce the calcium level
in the blood stream. Thus, the hormones parathormone of the parathyroids and
calcitonin of the ultimobranchial bodies must be in balance if the calcium
levels in the blood are to be in balance to
requirements.
Pineal body
The pineal
body is a very small gland located above the mid-brain. Using tryptophan (an
amino acid) it produces melatonin. Melatonin affects sleep, behaviour and brain
electrical activity. Thus the pineal body acts as a biological clock and as such
has an effect on the activities of the hypothalamus and its production of
releasing factors.
Islets of
langerhans
These are
small clumps of special cells located in the pancreas, which sits in the
duodenal loop of the small intestine. These special cells produce two
hormones:
- Insulin – lowers
blood sugar - Glucagon – increases
blood sugar and affects fatty acid
levels
Gonads
The sex
organs of males and females are called the gonads. These organs produce hormones
called sex hormones and include:
- Oestrogen.
- Testosterone.
- Progesterone.
males and females produce and need all three hormones but in different amounts.
When a male is castrated, for example, the balance of the sex hormones is
affected, leading to the bird taking on female characteristics. This means that
a capon or castrated male will, over time, take on much of the appearance and
behavior of a female.
THE JERSEY COW
IMMUNE-The immune system is
responsible for recognizing, resisting, and eliminating health challenges,
including pathogens, injuries, parasites, and stress. The immune system should
react and work fast when necessary so the productive functions of the animal are
not impaired. Therefore, a competent immune system is fundamental for optimal
cattle performance. In general, the immune system can be separated into two
components: the innate system and the adaptive system (Figure 1).Although both
systems have different features and functions, they are highly integrated and
work in harmony to provide adequate immune protection to the animal.
Innate Immune System
This
system is the first line of defense against any health challenge. It is
constituted by physical barriers and cellular components that do not react
specifically to the health challenge or disease that the animal acquires (Figure
1). This means that the innate immune system will respond similarly to different
pathogens, injuries, or stressors, but often not efficiently enough to resist
and eliminate complex disease conditions. However, the innate immune system is
triggered almost immediately after the animal is exposed to health challenges.
This characteristic of the innate system provides the time required by the
adaptive system to develop a specific and more efficient response, which may
take up to several days
The
major components of the innate immune
system are:
Physical Barriers - Includes the skin, mucosa,
and fluids such as saliva and tears. The main function of physical barriers is
to prevent pathogens such as viruses, bacteria, and parasites from entering the
body and causing infection.
Cellular components – Mainly constituted by
white blood cells that provide protection by ingesting and killing pathogens
that eventually enter the body. These cells are also responsible for secreting
substances that will further enhance the innate immune
response.
Inflammatory response –When
pathogens enter the body, white blood cells are mobilized to track and attack
them. If the pathogen is not eliminated quickly, white blood cells start
producing several substances that triggers an inflammatory response that is
needed to recruit additional immune cells to fight the infection. If the
infection occurs because of an injury that breaks the skin, the innate immune
system enhances blood flow to the injury site to increase the number of white
blood cells in that area, which is why the injured area rapidly becomes red,
warm, swollen, and very sensitive to touch. If the invading pathogen not rapidly
eliminated and the inflammation process persists, it leads to fever. Increased
body temperature helps with infection control and elimination because some
viruses and bacteria do not survive
higher temperatures, whereas many immunological processes become
further stimulated. However, prolonged inflammation and fever are harmful to the
animal’s overall health; therefore the infection needs to be eliminated quickly
to prevent further immune complications. If the health challenge is not
eliminated by the innate immune system, the adaptive system takes over. This
transition is mediated by some of the white blood cells from the innate system,
which “introduces” the foreign agent to specific cells from the adaptive system
for activation of this immune response.
Adaptive Immune System
This system adapts and builds a precise immune response for each challenge that the
animal encounters. However, it takes longer to become effective compared to the
innate immune system, sometimes up to several days following the infection. The
adaptive system is characterized by production of antibodies that are specific
for each foreign pathogen, and also by its “memory” feature. If the animal is
infected a second time by a pathogen, the adaptive system remembers the first
infection and elicits a faster and stronger response to eliminate the pathogen
(Figure 2). This “memory” feature is the foundation for the development of
vaccines to protect animals from specific diseases. The adaptive system can be
further divided into an antibody response and a cell-mediated response (Figure
1). The major components of the
adaptive immune system are:
Lymphoid
organs – These organs are responsible
for producing and activating the immune cells that mediate the adaptive immune
system. In general, the bone marrow produces B cells, whereas the thymus
produces the T cells. Both B and T cells are activated in the spleen or lymph
nodes, where they encounter the pathogen “presented” by white blood cells from
the innate immune system.
B cells
– These are the cells responsible for
secreting antibodies. When the B cell encounters the pathogen, it begins to
divide and produce antibodies that are specific for that pathogen. These
antibodies will attach to every target pathogen that they encounter, and will
either neutralize it, or “mark” the pathogen for ingestion or destruction by
other cells, such as white blood cells, T cells, and even B cells. Some B cells
are also responsible for the “memory” feature of the adaptive immune system.
These “memory” cells will record the pathogen’s genetic composition, and
register which antibody needs to be produced to eliminate the
pathogen.
T cells
– They are responsible for eliminating
cells containing the pathogen (cellmediated response). Similarly to B cells, the
T cells begin to multiply and become specific to the “presented” pathogen. When
activated T cells encounter white blood cells and B cells that
have ingested the specific pathogen they attack and eliminate
the whole cell-pathogen complex.
Active and passive immunity – Immunity is the
resistance of the animal to a specific
disease.
Active immunity is acquired when the animal is infected
by a specific pathogen, creates a “memory” against it, and successfully
eliminates the disease and pathogen. The next time the animal is infected by
the pathogen, the adaptive immune response will be faster and stronger (Figure
2), quickly eliminating the pathogen and preventing the disease. A common
example is chicken pox in humans; once you have it you’ll never have it again.
Vaccination is also an example of active immunity. By injecting the animal with
a killed or weakened pathogen, which won’t be harmful enough to develop the
disease, the immune system creates the “memory” and learns how to fight it if
an infection occurs. Passive immunity occurs when the animal receives
antibodies from an external source, such as another animal. The classical
example of passive immunity is the transfer of antibodies from the cow to the
calf via colostrum. This transfer is extremely important to newborn calves
because their immune system is not mature enough to develop its own antibodies.
The calf should be immune to most of the pathogens
present in the environment because the dam has already been exposed to them and developed
protective antibodies. Another example of passive immunity is the administration of specific antiserum or antitoxin to sick cattle or calves that
did not receive enough colostrum.
IMMUNE-The immune system is
responsible for recognizing, resisting, and eliminating health challenges,
including pathogens, injuries, parasites, and stress. The immune system should
react and work fast when necessary so the productive functions of the animal are
not impaired. Therefore, a competent immune system is fundamental for optimal
cattle performance. In general, the immune system can be separated into two
components: the innate system and the adaptive system (Figure 1).Although both
systems have different features and functions, they are highly integrated and
work in harmony to provide adequate immune protection to the animal.
Innate Immune System
This
system is the first line of defense against any health challenge. It is
constituted by physical barriers and cellular components that do not react
specifically to the health challenge or disease that the animal acquires (Figure
1). This means that the innate immune system will respond similarly to different
pathogens, injuries, or stressors, but often not efficiently enough to resist
and eliminate complex disease conditions. However, the innate immune system is
triggered almost immediately after the animal is exposed to health challenges.
This characteristic of the innate system provides the time required by the
adaptive system to develop a specific and more efficient response, which may
take up to several days
The
major components of the innate immune
system are:
Physical Barriers - Includes the skin, mucosa,
and fluids such as saliva and tears. The main function of physical barriers is
to prevent pathogens such as viruses, bacteria, and parasites from entering the
body and causing infection.
Cellular components – Mainly constituted by
white blood cells that provide protection by ingesting and killing pathogens
that eventually enter the body. These cells are also responsible for secreting
substances that will further enhance the innate immune
response.
Inflammatory response –When
pathogens enter the body, white blood cells are mobilized to track and attack
them. If the pathogen is not eliminated quickly, white blood cells start
producing several substances that triggers an inflammatory response that is
needed to recruit additional immune cells to fight the infection. If the
infection occurs because of an injury that breaks the skin, the innate immune
system enhances blood flow to the injury site to increase the number of white
blood cells in that area, which is why the injured area rapidly becomes red,
warm, swollen, and very sensitive to touch. If the invading pathogen not rapidly
eliminated and the inflammation process persists, it leads to fever. Increased
body temperature helps with infection control and elimination because some
viruses and bacteria do not survive
higher temperatures, whereas many immunological processes become
further stimulated. However, prolonged inflammation and fever are harmful to the
animal’s overall health; therefore the infection needs to be eliminated quickly
to prevent further immune complications. If the health challenge is not
eliminated by the innate immune system, the adaptive system takes over. This
transition is mediated by some of the white blood cells from the innate system,
which “introduces” the foreign agent to specific cells from the adaptive system
for activation of this immune response.
Adaptive Immune System
This system adapts and builds a precise immune response for each challenge that the
animal encounters. However, it takes longer to become effective compared to the
innate immune system, sometimes up to several days following the infection. The
adaptive system is characterized by production of antibodies that are specific
for each foreign pathogen, and also by its “memory” feature. If the animal is
infected a second time by a pathogen, the adaptive system remembers the first
infection and elicits a faster and stronger response to eliminate the pathogen
(Figure 2). This “memory” feature is the foundation for the development of
vaccines to protect animals from specific diseases. The adaptive system can be
further divided into an antibody response and a cell-mediated response (Figure
1). The major components of the
adaptive immune system are:
Lymphoid
organs – These organs are responsible
for producing and activating the immune cells that mediate the adaptive immune
system. In general, the bone marrow produces B cells, whereas the thymus
produces the T cells. Both B and T cells are activated in the spleen or lymph
nodes, where they encounter the pathogen “presented” by white blood cells from
the innate immune system.
B cells
– These are the cells responsible for
secreting antibodies. When the B cell encounters the pathogen, it begins to
divide and produce antibodies that are specific for that pathogen. These
antibodies will attach to every target pathogen that they encounter, and will
either neutralize it, or “mark” the pathogen for ingestion or destruction by
other cells, such as white blood cells, T cells, and even B cells. Some B cells
are also responsible for the “memory” feature of the adaptive immune system.
These “memory” cells will record the pathogen’s genetic composition, and
register which antibody needs to be produced to eliminate the
pathogen.
T cells
– They are responsible for eliminating
cells containing the pathogen (cellmediated response). Similarly to B cells, the
T cells begin to multiply and become specific to the “presented” pathogen. When
activated T cells encounter white blood cells and B cells that
have ingested the specific pathogen they attack and eliminate
the whole cell-pathogen complex.
Active and passive immunity – Immunity is the
resistance of the animal to a specific
disease.
Active immunity is acquired when the animal is infected
by a specific pathogen, creates a “memory” against it, and successfully
eliminates the disease and pathogen. The next time the animal is infected by
the pathogen, the adaptive immune response will be faster and stronger (Figure
2), quickly eliminating the pathogen and preventing the disease. A common
example is chicken pox in humans; once you have it you’ll never have it again.
Vaccination is also an example of active immunity. By injecting the animal with
a killed or weakened pathogen, which won’t be harmful enough to develop the
disease, the immune system creates the “memory” and learns how to fight it if
an infection occurs. Passive immunity occurs when the animal receives
antibodies from an external source, such as another animal. The classical
example of passive immunity is the transfer of antibodies from the cow to the
calf via colostrum. This transfer is extremely important to newborn calves
because their immune system is not mature enough to develop its own antibodies.
The calf should be immune to most of the pathogens
present in the environment because the dam has already been exposed to them and developed
protective antibodies. Another example of passive immunity is the administration of specific antiserum or antitoxin to sick cattle or calves that
did not receive enough colostrum.
HUMANS
Endocrine System- By using a series of signals, the glands of the endocrine system create
a communication network known as an axis. Endocrinologists study this system and
its relation to diabetes, obesity and other endocrine
conditions.
How does the endocrine system work? The basic way the endocrine system
works is through an elaborate structure of glands, each secreting hormones.
Endocrine glands work similar to nerves in that they rely on various signals to
operate, releasing the hormones depending on external and internal information.
In this way, the system can regulate nearly every function of the human body
from metabolism to general mood. Among the most important aspects of the
endocrine system is growth and development of tissues and organs. When a person studies how the
endocrine system works, the branch of science is known as
endocrinology.
Signaling in the Endocrine System
How does the endocrine system work with signals? Glands of the
endocrine system receive signals from outside stimuli. When a particular gland
determines it is time to release a hormone, it signals other glands and
hormone-producing agents to likewise release signals. This is called an axis.
Each gland and organ work in unison to achieve a goal. For example, if a person
is stimulated from some form of excitement, the hypothalamus sends out a signal to the pituitary gland, which in
turn sends a signal to produce adrenaline in the adrenal glands. Secondary
hormones are also released during this process which impacts the immune system,
digestion, and energy expenditure.
Additional types of endocrine signaling exist on the cellular level.
While these still work with hormones, the level of production is far smaller
than axis signaling. Autocrine signaling takes place within the cell itself,
when a hormone is released through a chemical messenger that binds with
receptors, creating a change in the cell. Juxtacrine signaling occurs between
adjacent cells with plasma membranes in contact with each other. This causes
actions in the adjacent cell or within both
cells.
Malfunctions in the Endocrine System
Commonly, things go wrong with the endocrine system that can affect the
way glands work and thereby the entire human body in general. A wide variety of
disorders and diseases can develop either over the course of time or suddenly which cause drastic
problems. Among the most common examples of these disorders are diabetes,
hypothyroidism, obesity and the development of
goiters.
These conditions are known as endocrinopathies and are divided into
three different formats: primary, secondary, and tertiary. Primary
endocrinopathies are the result of a failure of the glands to produce hormones.
Secondary conditions are those associated only with the pituitary gland, often
caused by tumors known as adenomas. Tertiary concerns are those where the
hypothalamus fails to function properly. This condition can result in
large-scale glandular failure.
How does the endocrine system work when a disease develops? A variety
of situations can arise when a person develops a endocrinopathy. The most common
is irregular hormone production, misinterpreting signals or releasing too many
hormones at one time. However, other conditions such as enlargements or a loss
of a gland can lead to these problems.
Immune System-
The immune system defends the body from attack by invaders recognized
as foreign. It is an extraordinarily complex system that relies on an elaborate
and dynamic communications network that exists among the many different kinds
of immune system cells that patrol the body. At the heart of the system is the
ability to recognize and respond to substances called antigens
whether they are infectious agents or part of the body (self antigens).
T and B
Cells
Most immune system cells are white
blood cells, of which there are many types. Lymphocytes are one type of white
blood cell, and two major classes of lymphocytes are T
cells
and B
cells.
T cells are critical immune system cells that help to destroy infected cells and
coordinate the overall immune response. The T cell has a molecule on its
surface called the T-cell
receptor.
This receptor interacts with molecules called MHC
(major histocompatibility complex).
MHC molecules are on the surfaces of most other cells of the body and help T
cells recognize antigen fragments. B cells are best known for making antibodies.
An antibody binds to an antigen and marks the antigen for destruction by other
immune system cells. Other types of white blood cells include macrophages
and neutrophils.
Macrophages and Neutrophils
Macrophages and neutrophils circulate in the blood and survey the body for
foreign substances. When they find foreign antigens, such as bacteria, they
engulf and destroy them. Macrophages and neutrophils destroy foreign antigens
by making toxic molecules such as reactive
oxygen intermediate molecules.
If production of these toxic molecules continues unchecked, not only are the
foreign antigens destroyed, but tissues surrounding the macrophages and
neutrophils are also destroyed. For example, in individuals with the autoimmune
disease called Wegener's granulomatosis, overactive macrophages and neutrophils
that invade blood vessels produce many toxic molecules and contribute to damage
of the blood vessels. In rheumatoid arthritis, reactive oxygen intermediate
molecules and other toxic molecules are made by overproductive macrophages and
neutrophils invading the joints. The toxic molecules contribute to inflammation,
which is observed as warmth and swelling, and participate in damage to the
joint.
MHC and Co-Stimulatory Molecules
MHC molecules are found on all cell surfaces and are an active part of
the body's defense team. For example, when a virus infects a cell, a MHC
molecule binds to a piece of a virus (antigen) and displays the antigen on the
cell's surface. Cells that have the capability of displaying antigen with MHC
are called antigen-presenting cells. Each MHC molecule that displays an antigen
is recognized by a matching or compatible T-cell receptor. Thus, an antigen-presenting
cell
is able to communicate with a T cell about what may be occurring inside the
cell. However, for the T cell to respond to a foreign antigen on the MHC,
another molecule on the antigen-presenting cell must send a second signal to the
T cell. A corresponding molecule on the surface of the T cells recognizes the
second signal. These two secondary molecules of the antigen-presenting cell and
the T cell are called co-stimulatory molecules. There are several different sets
of co-stimulatory molecules that can participate in the interaction of
antigen-presenting cell with a T cell.
Once the MHC and the T-cell
receptor interact, and the co-stimulatory molecules interact, there are several
possible paths that the T cell may take. These include T cell activation,
tolerance, or T cell death. The subsequent steps depend in part on which
co-stimulatory molecules interact and how well they interact. Because these
interactions are so critical to the response of the immune system, researchers
are intensively studying them to find new therapies that could control or stop
the immune system attack on self tissues and organs.
Cytokines and Chemokines
One
way T cells can respond after the interaction of the MHC and the T-cell
receptor, and the interaction of the co-stimulatory molecules, is to secrete
cytokines and chemokines. Cytokines are proteins that may cause surrounding
immune system cells to become activated, grow, or die. They also may influence
non-immune system tissues. For example, some cytokines may contribute to the
thickening of the skin that occurs in people with scleroderma.
Chemokines are small cytokine molecules that attract cells of the immune
system. Overproduction of chemokines contributes to the invasion and
inflammation of the target organ, which occurs in autoimmune diseases. For
example, overproduction of chemokines in the joints of people with rheumatoid
arthritis may result in invasion of the joint space by destructive immune
system cells such as macrophages, neutrophils, and T cells.
Antibodies
B cells are
another critical type of immune system cell. They participate in the removal of
foreign antigens from the body by using a surface molecule to bind the antigen
or by making specific antibodies that can search out and destroy specific
foreign antigens. However, the B cell can only make antibodies when it receives
the appropriate command signal from a T cell. Once the T cell signals the B cell
with a type of cytokine that acts as a messenger molecule, the B cell is able to
produce a unique antibody that targets a particular antigen.
Autoantibodies
In some
autoimmune diseases, B cells mistakenly make antibodies against tissues of the
body (self antigens) instead of foreign antigens. Occasionally, these
autoantibodies either interfere with the normal function of the tissues or
initiate destruction of the tissues. People with myasthenia gravis experience
muscle weakness because autoantibodies attack a part of the nerve that
stimulates muscle movement. In the skin disease pemphigus vulgaris,
autoantibodies are misdirected against cells in the skin. The accumulation of
antibodies in the skin activates other molecules and cells to break down,
resulting in skin blisters.
Immune Complexes and the Complement
System
When many antibodies are bound to
antigens in the bloodstream, they form a large lattice network called an
immune
complex.
Immune complexes are harmful when they accumulate and initiate inflammation
within small blood vessels that nourish tissues. Immune complexes, immune cells,
and inflammatory molecules can block blood flow and ultimately destroy organs
such as the kidney. This can occur in people with systemic lupus erythematous.
A group of specialized molecules that form the complement
system
helps to remove immune complexes. The different types of molecules of the
complement system, which are found in the bloodstream and on the surfaces of
cells, make immune complexes more soluble. Complement molecules prevent
formation and reduce the size of immune complexes so they do not accumulate in
the wrong places (organs and tissues of the body). Rarely, some people inherit
defective genes for a complement molecule from their parents. Because these
individuals cannot make a normal amount or type of complement molecule, their
immune systems are unable to prevent immune complexes from being deposited in
different tissues and organs. These people develop a disease that is not
autoimmune but resembles lupus erythematous.
Genetic Factors
Genetic
factors can affect an individual's immune system and its responses to foreign
antigens in several ways. Genes determine the variety of MHC molecules that
individuals carry on their cells. Genes also influence the potential array of
T-cell receptors present on T cells. In fact, some MHC genes are associated with
autoimmune diseases. However, genes are not the only factors involved in
determining a person's susceptibility to an autoimmune disease. For example,
some individuals who carry disease-associated MHC molecules on their cells will
not develop an autoimmune disease.
Endocrine System- By using a series of signals, the glands of the endocrine system create
a communication network known as an axis. Endocrinologists study this system and
its relation to diabetes, obesity and other endocrine
conditions.
How does the endocrine system work? The basic way the endocrine system
works is through an elaborate structure of glands, each secreting hormones.
Endocrine glands work similar to nerves in that they rely on various signals to
operate, releasing the hormones depending on external and internal information.
In this way, the system can regulate nearly every function of the human body
from metabolism to general mood. Among the most important aspects of the
endocrine system is growth and development of tissues and organs. When a person studies how the
endocrine system works, the branch of science is known as
endocrinology.
Signaling in the Endocrine System
How does the endocrine system work with signals? Glands of the
endocrine system receive signals from outside stimuli. When a particular gland
determines it is time to release a hormone, it signals other glands and
hormone-producing agents to likewise release signals. This is called an axis.
Each gland and organ work in unison to achieve a goal. For example, if a person
is stimulated from some form of excitement, the hypothalamus sends out a signal to the pituitary gland, which in
turn sends a signal to produce adrenaline in the adrenal glands. Secondary
hormones are also released during this process which impacts the immune system,
digestion, and energy expenditure.
Additional types of endocrine signaling exist on the cellular level.
While these still work with hormones, the level of production is far smaller
than axis signaling. Autocrine signaling takes place within the cell itself,
when a hormone is released through a chemical messenger that binds with
receptors, creating a change in the cell. Juxtacrine signaling occurs between
adjacent cells with plasma membranes in contact with each other. This causes
actions in the adjacent cell or within both
cells.
Malfunctions in the Endocrine System
Commonly, things go wrong with the endocrine system that can affect the
way glands work and thereby the entire human body in general. A wide variety of
disorders and diseases can develop either over the course of time or suddenly which cause drastic
problems. Among the most common examples of these disorders are diabetes,
hypothyroidism, obesity and the development of
goiters.
These conditions are known as endocrinopathies and are divided into
three different formats: primary, secondary, and tertiary. Primary
endocrinopathies are the result of a failure of the glands to produce hormones.
Secondary conditions are those associated only with the pituitary gland, often
caused by tumors known as adenomas. Tertiary concerns are those where the
hypothalamus fails to function properly. This condition can result in
large-scale glandular failure.
How does the endocrine system work when a disease develops? A variety
of situations can arise when a person develops a endocrinopathy. The most common
is irregular hormone production, misinterpreting signals or releasing too many
hormones at one time. However, other conditions such as enlargements or a loss
of a gland can lead to these problems.
Immune System-
The immune system defends the body from attack by invaders recognized
as foreign. It is an extraordinarily complex system that relies on an elaborate
and dynamic communications network that exists among the many different kinds
of immune system cells that patrol the body. At the heart of the system is the
ability to recognize and respond to substances called antigens
whether they are infectious agents or part of the body (self antigens).
T and B
Cells
Most immune system cells are white
blood cells, of which there are many types. Lymphocytes are one type of white
blood cell, and two major classes of lymphocytes are T
cells
and B
cells.
T cells are critical immune system cells that help to destroy infected cells and
coordinate the overall immune response. The T cell has a molecule on its
surface called the T-cell
receptor.
This receptor interacts with molecules called MHC
(major histocompatibility complex).
MHC molecules are on the surfaces of most other cells of the body and help T
cells recognize antigen fragments. B cells are best known for making antibodies.
An antibody binds to an antigen and marks the antigen for destruction by other
immune system cells. Other types of white blood cells include macrophages
and neutrophils.
Macrophages and Neutrophils
Macrophages and neutrophils circulate in the blood and survey the body for
foreign substances. When they find foreign antigens, such as bacteria, they
engulf and destroy them. Macrophages and neutrophils destroy foreign antigens
by making toxic molecules such as reactive
oxygen intermediate molecules.
If production of these toxic molecules continues unchecked, not only are the
foreign antigens destroyed, but tissues surrounding the macrophages and
neutrophils are also destroyed. For example, in individuals with the autoimmune
disease called Wegener's granulomatosis, overactive macrophages and neutrophils
that invade blood vessels produce many toxic molecules and contribute to damage
of the blood vessels. In rheumatoid arthritis, reactive oxygen intermediate
molecules and other toxic molecules are made by overproductive macrophages and
neutrophils invading the joints. The toxic molecules contribute to inflammation,
which is observed as warmth and swelling, and participate in damage to the
joint.
MHC and Co-Stimulatory Molecules
MHC molecules are found on all cell surfaces and are an active part of
the body's defense team. For example, when a virus infects a cell, a MHC
molecule binds to a piece of a virus (antigen) and displays the antigen on the
cell's surface. Cells that have the capability of displaying antigen with MHC
are called antigen-presenting cells. Each MHC molecule that displays an antigen
is recognized by a matching or compatible T-cell receptor. Thus, an antigen-presenting
cell
is able to communicate with a T cell about what may be occurring inside the
cell. However, for the T cell to respond to a foreign antigen on the MHC,
another molecule on the antigen-presenting cell must send a second signal to the
T cell. A corresponding molecule on the surface of the T cells recognizes the
second signal. These two secondary molecules of the antigen-presenting cell and
the T cell are called co-stimulatory molecules. There are several different sets
of co-stimulatory molecules that can participate in the interaction of
antigen-presenting cell with a T cell.
Once the MHC and the T-cell
receptor interact, and the co-stimulatory molecules interact, there are several
possible paths that the T cell may take. These include T cell activation,
tolerance, or T cell death. The subsequent steps depend in part on which
co-stimulatory molecules interact and how well they interact. Because these
interactions are so critical to the response of the immune system, researchers
are intensively studying them to find new therapies that could control or stop
the immune system attack on self tissues and organs.
Cytokines and Chemokines
One
way T cells can respond after the interaction of the MHC and the T-cell
receptor, and the interaction of the co-stimulatory molecules, is to secrete
cytokines and chemokines. Cytokines are proteins that may cause surrounding
immune system cells to become activated, grow, or die. They also may influence
non-immune system tissues. For example, some cytokines may contribute to the
thickening of the skin that occurs in people with scleroderma.
Chemokines are small cytokine molecules that attract cells of the immune
system. Overproduction of chemokines contributes to the invasion and
inflammation of the target organ, which occurs in autoimmune diseases. For
example, overproduction of chemokines in the joints of people with rheumatoid
arthritis may result in invasion of the joint space by destructive immune
system cells such as macrophages, neutrophils, and T cells.
Antibodies
B cells are
another critical type of immune system cell. They participate in the removal of
foreign antigens from the body by using a surface molecule to bind the antigen
or by making specific antibodies that can search out and destroy specific
foreign antigens. However, the B cell can only make antibodies when it receives
the appropriate command signal from a T cell. Once the T cell signals the B cell
with a type of cytokine that acts as a messenger molecule, the B cell is able to
produce a unique antibody that targets a particular antigen.
Autoantibodies
In some
autoimmune diseases, B cells mistakenly make antibodies against tissues of the
body (self antigens) instead of foreign antigens. Occasionally, these
autoantibodies either interfere with the normal function of the tissues or
initiate destruction of the tissues. People with myasthenia gravis experience
muscle weakness because autoantibodies attack a part of the nerve that
stimulates muscle movement. In the skin disease pemphigus vulgaris,
autoantibodies are misdirected against cells in the skin. The accumulation of
antibodies in the skin activates other molecules and cells to break down,
resulting in skin blisters.
Immune Complexes and the Complement
System
When many antibodies are bound to
antigens in the bloodstream, they form a large lattice network called an
immune
complex.
Immune complexes are harmful when they accumulate and initiate inflammation
within small blood vessels that nourish tissues. Immune complexes, immune cells,
and inflammatory molecules can block blood flow and ultimately destroy organs
such as the kidney. This can occur in people with systemic lupus erythematous.
A group of specialized molecules that form the complement
system
helps to remove immune complexes. The different types of molecules of the
complement system, which are found in the bloodstream and on the surfaces of
cells, make immune complexes more soluble. Complement molecules prevent
formation and reduce the size of immune complexes so they do not accumulate in
the wrong places (organs and tissues of the body). Rarely, some people inherit
defective genes for a complement molecule from their parents. Because these
individuals cannot make a normal amount or type of complement molecule, their
immune systems are unable to prevent immune complexes from being deposited in
different tissues and organs. These people develop a disease that is not
autoimmune but resembles lupus erythematous.
Genetic Factors
Genetic
factors can affect an individual's immune system and its responses to foreign
antigens in several ways. Genes determine the variety of MHC molecules that
individuals carry on their cells. Genes also influence the potential array of
T-cell receptors present on T cells. In fact, some MHC genes are associated with
autoimmune diseases. However, genes are not the only factors involved in
determining a person's susceptibility to an autoimmune disease. For example,
some individuals who carry disease-associated MHC molecules on their cells will
not develop an autoimmune disease.