Endocrine System The endocrine system is a
collectionofspecialized body tissues and organs that produce,
store, and secrete chemical substances that transfer information
and instructions from one set of cells to another. These chemical
substance called hormones are secreted to the blood where it is
transported to the rest of the body and absorbed by target tissues.
These three, chemical signals, receptors and glands comprises the
endocrine system.I. Functions:
1. Regulation of bodys activities (reproduction, growth and
development, body to achieve homeostasis (state of
equilibrium).
2. The endocrine system regulates the growth of tissues, as well
as its rate of metabolism. Metabolism is the way by which chemical
reactions by which the cells of an organism transform energy,
maintain their identity, and reproduce.
3. The endocrine system influences the maturation of tissues,
which causes the development of adult features and behavior.4.
Blood components control
a. Water balance through maintaining a balanced solute
concentration.
b. Ion regulation for it regulates Na+, K+, and Ca2+
concentrations in the blood.
c. Blood glucose control is also performed by the system as well
as other nutrients in the blood.
5. The system controls as well the development and functions of
the reproductive system, as well as uterine contractions during the
delivery of newborns and milk release from lactating females.
6. The endocrine system helps regulate as well the heart rate
and blood pressure.
7. The endocrine system plays a crucial role as well in helps
control the production and functions of immune cells.
II. Three Key Areas
A. Chemical signals
Hormones chemical signals secreted by cells into the
extracellular fluids and regulate metabolic activity of other
cells. From its etymology itself to arouse, it brings about changes
in other cells by increasing or decreasing the rate of a normal or
usual metabolic process. Typically, one or more of the following
occurs:
a. changes in plasma membrane permeability or electrical
state
b. synthesis of proteins or enzymes
c. activation or inactivation of enzymes
d. stimulation of mitosis
Hormones of the endocrine system reaches nearly every living
cell, have specific targets ,whcich means that each kind acts only
on certain cell and are called target cells and its control tend to
be slower than that of the nervous system. Hormones can either
be:
a. Proteins/non-steroid
Proteins, peptides, and amino acid derivatives, hormones in this
category are lipid insoluble thus, bind to membrane bound receptors
on the
2 cells surface, and their binding either opens or closes cell
membrane ion channels or activates enzymes within the cell
b. Lipids/steroids
Steroid hormones, all of which are derived from cholesterol, are
lipid soluble and can enter the cells called intercellular chemical
signals. (better illustration for both kinds in the next part).
B. Receptors
1. Membrane Bound Receptors extend through the cell membrane,
with their receptor sites on the outer surface of the cell
membrane. When chemical signals bind to these receptors, the part
of the receptor that is inside the cell produces a response. There
are three major mechanisms by which they do this:
a. Receptors that directly alter membrane permeability. In this
case, once chemical signals bind to the receptor sites, ion
channels open or close. That change in membrane permeability alters
the movements of ions across the cell membrane, which is
responsible for the response.
3
b. Receptors and G proteins. This time, when chemical signals
bind o the receptor, the result is the activation of the complex of
G protein, which has alpha (), beta() and gamma() as subunits bound
together. Guanosine Diphosphate (GDP) is bound to the alpha()
subunit. Once this happens, the alpha subunit separates from the
beta and gamma, and from GDP, Guanosine Triphospate is now bounded
to it, and this GTP can either open or close membrane channels,
activate enzymes that produce intracellular chemical signals or
affect gene expression.
c. Receptors that directly alter the activity of enzymes. This
happens in here ways: From the heading itself, inactive enzymes are
directly affected and become active once these messages bind.
Moreover, when these chemical messages bind, they activate the
enzyme guanylate cyclase which converts GTP to cyclic GMP (cGMP)
plus two inorganic phosphate groups (PPi). this activated enzyme
then alters other intracellular enzymes to produce a response.
Lastly, once these messages bind, they may turn inactive or
unphospholyrated sites to phosphorylated ones which produce a
response inside the cell.
42. Intracellular Receptors are where small and lipid soluble
messages bind to, once they enter the cells, they may be enzymes or
even the DNA, which is the ultimate goal. Anyhow, once the chemical
messages enter, they make their way to the nucleus to bind to a
specific receptor protein in there. It then binds to specific areas
on the DNA activating certain genes to transcribe messenger RNA
(mRNA). The mRNA then is transmitted to the cytoplasm for the
production of new proteins. Comparing the two processes, those
chemical messages that bin to membrane bound receptors produce
rapid responses. This is because a few intercellular chemical
signal molecules can bind to their receptors and each activated
receptor can produce many intracellular messages. These in turn,
rapidly activate many enzymes inside the cell. What happens is
called a cascade effect. On the other hand, it takes several hours
for the new synthesis of mRNA and proteins to finish.
3. Hormone Secretion RegulationIn maintaining homeostasis inside
the body, it is important that hormones and blood levels of
compounds are just around the perfect amount, and the endocrine
system does this through the negative feedback mechanism. In here,
controlled variables (blood sugar, calcium etc.) and changes in its
normal values are corrected by glands by secreting more or less of
that hormone. Such negative feedback loop is a stable,
self-adjusting mechanism for maintaining homeostasis of the
controlled variable.
Another way is through hormone secretion itself. This way,
specific hormones are released to trigger the secretion of another
(eg. pituitary to ovary/testes). Lastly, some hormone secretion is
controlled by the nervous system (eg. epinephrine released from
adrenal medulla which is triggered by the nervous system
stimulation.
5III. Endocrine Glands and their HormonesPancreas
Pancreas is a mixed glandular organ that is located close to the
stomach in the abdominal cavity. As a mixed gland, the pancreas has
exocrine function which act as part of the digestive system that
produces digestive enzymes, and the endocrine function which
produces and secretes hormones. Additionally, the regions of the
pancreas that contain its endocrine cells are called pancreatic
islets, formerly called islets of Langerhans. The islets are a
compact collection of endocrine cells arranged in clusters and
cords and are crisscrossed by a dense network of capillaries. The
capillaries of the islets are lined by layers ofendocrinecells in
direct contact with vessels, and most endocrine cells are in direct
contact withblood vessels, by eithercytoplasmic processes or by
direct apposition.
Glucagon and insulin are the two important hormones produced by
the Alpha and Beta cells, respectively in the pancreatic islets.
The glucagon increases the breakdown of glycogen (a moleculethat
functions as the secondary long-termenergy
storageinanimalandfungalcells) and release of glucose into the
cardiovascular system which in effect, raises blood sugar. On the
other hand, the insulin increases uptake and use of glucose and
amino acids which in effect, lowers blood sugar.
Because of these two hormones, the body maintains normal range
of values of blood sugar levels. A decline in the blood glucose
level below its normal range causes the nervous system to
malfunction because glucose is the nervous systems main source of
energy. Furthermore, if blood glucose levels are too high, the
kidneys produce large volumes of urine containing substantial
amounts of glucose. Dehydration can result because of the rapid
loss of water in the body.
Adrenal Gland
6
Adrenal glands, which are also called suprarenal glands, are
small, triangular glands located on top of both kidneys. An adrenal
gland is made of two parts: the outer region is called the adrenal
cortex and the inner region is called the adrenal medulla.
Both parts of the adrenal glands: the adrenal cortex and the
adrenal medulla perform very separate functions.
The adrenal cortex, the outer portion of the adrenal gland,
secretes hormones that have an effect on the body's metabolism, on
chemicals in the blood, and on certain body characteristics. The
adrenal cortex secretes corticosteroids and other hormones directly
into the bloodstream. The hormones produced by the adrenal cortex
include:
Mineralocorticoids (aldosterone) targets the kidneys primarily
and the intestine and sweat glands to a lesser degree. It increases
the rate of sodium transport into the body; increases the rate of
potassium excretion and secondarily favor water retention.
Glucocoricoids (cortisol) targets most tissues. It increases the
fat and protein breakdown, the glucose synthesis from amino acids,
blood nutrient levels, inhibits inflammation and immune
response.
Adrenal androgens also target most tissues. It is insignificant
in male. But in females, it increases their sexual drive, pubic
hair and axillary hair growth.
The adrenal medulla, the inner part of the adrenal gland helps a
person in coping with physical and emotional stress. The adrenal
medulla secretes the following hormones:
epinephrine(also called adrenaline) -this hormone increases the
heart rate and force of heart contractions, facilitates blood flow
to the muscles and brain, causes relaxation of smooth muscles,
helps with conversion of glycogen to glucose in the liver, and
other activities.
norepinephrine (also called noradrenaline) -this hormone has
little effect on smooth muscle, metabolic processes, and cardiac
output, increasing blood pressure.
The adrenal glands work interactively with the hypothalamus and
pituitary gland in the following process: the hypothalamus produces
corticotropin-releasing hormones, which stimulate the pituitary
gland and the pituitary gland, in turn, produces corticotropin
hormones, which stimulate the adrenal glands to produce
corticosteroid hormones.
Thymus Gland
7
Thymus gland is located between the lungs, behind the breastbone
and near the heart. Sometimes it is considered part of the
lymphatic system.
The thymus gland produces thymosin and thymopoietin which
targets the lymphocytes which are white blood cells that travel the
body through the bloodstream. It helps lymphocytes mature,
especially in children. The main function of the thymus gland is in
the processing and maturation of special lymphocytes called
T-cells.
The thymus gland is most active during early life, playing a
critical role in the development of a child's immune system before
birth and for a time thereafter. Usually by the age of two, the
thymus gland has reached its maximum size (weighing about 30 to 40
grams or 1.06 to 1.41 ounces) with the immune system becoming fully
functional. Because of this, vaccinations before the age of two are
not really necessary since these young immune systems are not
mature enough to handle the strength of a vaccine.
If thethymusglandis removed in infancy, theimmune systemwill
never fully develop. There is a great degree of infection risk in
patients who have nothymusgland, or whosethymusnever developed
properly. The majority of lymphocyte production happens early in
life, so thethymusglanddeteriorates with age. In youth,
thethymuswill reach the size of an apple, but it is reduced to the
size of a small marble in the elderly. By the time a person reaches
senior citizen status, it is likely their thymusis barely
discernible from surrounding fatty tissues. After puberty, the
gland begins to shrink and is replaced by connective tissue and
fat.
Parathyroid Gland
The parathyroid glands are tiny masses of glandular tissue most
often found on the position on the posterior surface of the thyroid
gland which produces parathyroid hormone (PTH). The parathyroid
hormone targets the tissues of the bone of kidney wherein it
increases the rate of bone breakdown by osteoclasts (a type ofbone
cellthat removesbone tissueby removing its mineralized matrix and
breaking up the organic bone) and PTH also increases vitamin D
synthesis that is essential for maintenance of normal blood calcium
levels. When blood calcium levels drop below a certain point,
thecalcium-sensing receptorsin the parathyroid gland are activated
to release hormone into the blood. Parathyroid also controls how
much calcium is in the bones, and therefore, how strong and dense
the bones are.However, thethyroidgland regulates the bodys
metabolism and has no effect on calcium levels while parathyroid
glands regulate calcium levels and have no effect on metabolism.
When the calcium in our blood goes too low, the parathyroid glands
makemorePTH. Increased PTH causes the body to put more calcium into
the blood. Increased PTH causes the bones to release their calcium
into the blood.Parathyroid hormone (PTH) has a very powerful
influence on the cells of the bones which causes them to release
their calcium into the bloodstream.When bones are exposed to high
levels of parathyroid hormone for several years they become brittle
and muchmore prone to fractures.If blood calcium levels fall too
law, neurons become extremely irritable and overactive.Pineal
Gland
The pineal gland is a small cone shaped gland found on the roof
of the third ventricle, near the center of the brain.
It is known to produce a derivative of the serotonin hormone,
melatonin. Levels of melatonin fluctuate during the course of a
day. This hormone plays a role in the bodys circadian rhythm. This
rhythm regulates the physiological functions that occur in the body
within a 24-hour period, such as sleep-wake cycles, fluctuations in
body temperature, heart rate, and blood pressure.
According to studies, melatonin is believed to be a sleep
trigger, making it crucial for the human bodys internal clock for
the day and night cycle. Also, it coordinates the hormones of
fertility and inhibits the reproductive system, so that sexual
maturation is prevented from occurring before adulthood.
Thyroid gland
An endocrine gland found in the neck area, near the parathyroid,
that controls metabolism and helps regulate the calcium balance of
the body.
The two main hormones it produces are: Thyroxine and Calcitonin.
Thyroxine is used in keeping the metabolism going, turning food
into energy, also it influences physical development. Calcitonin on
the on the hand promotes bone growth, stimulating the uptake of
calcium absorption by the bones also inhibiting the activity of
bone resorption. Another notable hormone is triiodothyronine.
Without the Thyroid, during childhood years, growth and
development would be impossible. Bones would not absorb calcium and
the food eaten would not be converted into energy used to promote
physical development.
Pituitary Gland
A small endocrine gland located below the hypothalamus about the
size of a grape. It is considered to be the master gland, secreting
eight different hormones and regulates majority of the other
endocrine glands. It consists of two lobes, a posterior lobe and an
anterior lobe. It is also known as hypophysis.
Anterior Pituitary
The anterior pituitary is responsible for releasing the growth
hormone, thus most cells are target cells. It also secretes the
Thyroid Stimulating Hormone (TSH) which increases the thyroid
hormone secretion. Moreover, it also secretes the
Adrenocorticotropic Hormone (ACTH) which increases cortisol
increasing skin pigmentation. Melanin also increases through its
secretion of the Melanocyte-stimulating Hormone. The Luteinizing
Hormone (LH) promotes ovulation and progesterone production in the
ovary, and sperm support and testosterone production in males.
Lastly, Prolactin is a hormone which stimulates milk production and
prolong progesterone secretion following ovulation and during
pregnancy in women.
Posterior Pituitary
The Antidiuretic Hormone (ADH) is secreted to increase water
absorption in the kidney so less water is excreted through urine.
Oxytocin increases uterine contractions and milk let down from
mammary glands.
The pituitary gland is considered the master gland. Any disorder
would cause problems in the production of sex cells and would
trigger a chain reaction leading to a dysfunctional thyroid gland,
adrenal gland and organ failure. 10
Ovaries
The ovaries are paired, almond-sized organs located in the
abdomen or pelvic cavity. Aside from producing female sex cells
(ova, or eggs), it also produce two groups of steroid hormones,
estrogens and progesterone.
During puberty, the anterior pituitary starts to release
luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
These hormones stimulate the ovaries to begin secreting estrogen
and progesterone. This results in the rhythmic ovarian cycles in
which ova develop and blood levels of ovarian hormones rise and
fall.
Estrogen, produced by the Graafian follicle of the ovaries,
initiates the development of female secondary sex characteristics
primarily growth and maturation of the reproductive organs and the
appearance of hair in the pubic and axillary regions and also so
such as breast development, widening pelvis, and distribution of
body fat. In addition, the estrogens work with progesterone to
prepare the uterus to receive a fertilized egg. This results in
cyclic changes in the uterine lining, which is called the menstrual
cycle. Estrogens also help maintain pregnancy and prepare the
breasts to produce milk (lactation). However, the placenta and not
the ovaries is the source of the estrogens at this time.
Progesterone quiets the muscles of the uterus during pregnancy
so that an implanted embryo will not be aborted and helps prepare
breast tissue for lactation. It is produced by another glandular
structure of the ovaries, the corpus luteum. The corpus luteum
produces both estrogen and progesterone but progesterone, is
secreted in larger amounts. Release of LH, FSH, estrogen, and
progesterone continues throughout a womans productive years.
Testes
The testes, located in the scrotum, produce androgens, the male
sex hormones. The primary androgen produced by males is
testosterone. During puberty the anterior pituitary gland begins to
release luteinizing hormone (LH), which stimulates the testes to
resume testosterone production. Testosterone causes development of
the adult male sex characteristics. It promotes the growth and
maturation of the reproductive system organs to prepare the young
man for reproduction. It also causes the males secondary sex
characteristics (growth of facial hair, development of heavy bones
and muscles, and deepening of the voice) to appear and stimulates
the male sex drive. LH, FSH, and testoseterone continue to maintain
the male reproductive system after puberty.OVARIES AND TESTES:
The adrenal glands in both sexes produce a small amount of a
testosterone-like androgen called dihydroepiandrosterone (DHEA).
DHEA has no demonstrable effect in males because they have an
abundance of the more powerful testosterone. In females, DHEA form
the adrenal glands is responsible for many of the same actions as
testosterone in males, including enhancement of the female puberta
growth, the development of axillary (armpit) and pubic hair, and
development and maintenance of the female sex drive.
Intestine
Cells in the lining of the stomach and small intestine secrete
hormones that stimulate the production of digestive juices from the
stomach, pancreas, and liver. These hormones aid the process of
digestion by causing secretion or digestive juices when food is
present in the digestive system but not at other times. Hormones
secreted from the small intestine also help regulate the rate at
which food passes from the stomach into the small intestine, so
that food enters the small intestine at an optimal rate.
Placenta
A temporary organ formed during pregnancy, produces hormones
generally thought of as ovarian hormones (estrogen and
progesterone). Placenta is a remarkable organ formed temporarily in
the uterus of pregnant women. In addition to its roles as the
respiratory, excretory, and nutrition-delivery systems for the
fetus, it also produces hormones that help to maintain the
pregnancy and pave the way for delivery of the baby.
During very early pregnancy, a hormone called human chronic
gonadotropin (hCG) is produced by the developing imbryo and then by
the fetal part of the placenta. Similar to LH (luteinizing
hormone), hCG stimulates the corpus luteum of the ovary to continue
producing estrogen and progesterone so that the lining of the
uterus is not sloughed off in menses. In the third month, the
placenta assumes the job of producing estrogen and progesterone,
and the ovaries become inactive for the rest of the pregnancy. The
high estrogen and progesterone blood levels maintain the lining of
the uterus (thus, the pregnancy) and prepare the breasts for
producing milk. Human placental lactogen (hPL) works cooperatively
with estrogen and progesterone in preparing the breasts for
lactation, and relaxing another placental hormone causes them to
relax and become more flexible, which eases birth passage. The
heart and the kidneys all have functions unrelated to the endocrine
system. Nevertheless, all of these organs secrete at least one
hormone.12
KidneysErythropoietin and renin are secreted by the kidneys.
Erythropoietin stimulates the production of red blood cells in bone
marrow. Renin ultimately stimulates aldosterone secretion and
constricts blood vessels.
Heart
Atrial natriuretic hormone (ANH) is a peptide (nonsteroid)
hormone secreted by the atria f the heart that helps regulate blood
pressure. When blood pressure rises, ANH increases the rate at
which sodium and water are excreted in urine. This decreases blood
volume and lowers blood pressure.
Common diseases of the Endocrine System
Because our Endocrine system is one of two primary systems for
controlling bodily functions, the other being the Nervous system,
any disruption or Homeostatic Imbalance to it can have dramatic and
widespread effects on the body. (Note: many disorders of this
system are often chronic conditions of too much (Hypersecretion) or
too little (Hyposecretion) Hormone, or tumors (benign or malignant)
of the endocrine glands; some of them are inherited condition.)
Here are some of its common disorders.
Hypersecretion of the Antidiuretic hormone (ADH) the ADH is a
hormone secreted in the Posterior Pituitary gland that targets the
kidney in reducing the amount of water thats lost in urine. This
condition is called syndrome of inappropriate ADH secretion
(SIADH). People who have SIADH retain too much water to be in a
state of water balance. This could result in Hyponatremia, an
electrolyte disorder, or fluid overload, a condition wherein there
is too much fluid in the blood. Some symptoms may include
headaches, nausea, and vomiting. Underlying disorders ranging from
HIV infection, meningitis and brain injuries to pneumonia or
chronic lung conditions can cause SIADH; some drugs that can
increase ADH production can also cause the condition.
Treatments for this condition may include:
a) Treating the underlying causes when possible (i.e. treatment
of the meningitis, pneumonia etc.)
b) Long term fluid restriction to lower or correct the water
imbalance and to increase serum sodium* (because of hyponatremia
wherein sodium concentration in theblood serumis lower than
normal.)
c) Drugs such as Demeclocycline, Conivaptan, Tolvaptan etc. that
are prescribed by physicians.
Diabetes Insipidus this disorder is the opposite of the SIADH
because instead of retaining too much water, the condition is
characterized by the inability to save water properly which is
caused by either the lack of ADH or by lack of the receptors for
ADH in kidney cells. The symptoms may include excessive thirst,
excretion of large amounts of severely diluted urine, with the
lessening of fluid intake having no effect on the latter; signs of
dehydration may also appear in some people since the body cannot
conserve much of the water that it takes in. Some cases of Diabetes
insipidus can be caused by head trauma or brain surgery that
disrupts the normal production of ADH. People with this condition
must to drink large amount of water in order to keep up with the
amount of water lost by their kidneys. 13Pituitary Dwarfism or
Growth Hormone Deficiency (GDH) this condition is caused by
Hyposecretion of the growth hormone during childhood. The Growth
Hormone (GH), from the Anterior Pituitary gland, is importantly
involved in the growth and development process of children
therefore abnormalities of growth hormone secretion are most
damaging when they happen before puberty. It is characterized by
having poor growth and/or shortness, and having cherubic facial
feature or that which resembles a kewpie doll. In order to correct
this disorder, it should be diagnosed early and treated with growth
hormone throughout childhood; otherwise, if the patient reaches
adulthood, even administering the growth hormone cannot overcome
the disorder. This is because during puberty, the sex steroid
hormones causes the cartilaginous growth plates at the ends of long
bones to be replaced by bone so after that, bones do not grow in
length again.
Gigantism this disorder is caused by hypersecretion or
overproduction of the growth hormone during childhood and
adolescence. Excess GH secretion can come from hormone-secreting
tumors on the pituitary gland. Exaggerated bone growth occurs when
excess GH is present before bones complete their growth in length,
this results in the person being abnormally tall. There is no known
cure for gigantism and many of those identified with it have
suffered multiple health problems regarding their circulatory and
skeletal system.
Acromegaly this disorder is similar to gigantism except it does
not make the individuals whole body grow abnormally taller, rather
it only makes some parts of the body grow to abnormal proportions.
This is because if the excess hormone is secreted after growth in
bone length is complete, the bone growth continues in diameter, but
not in length (the reason why this disorder is only common in
adults or those reaching adulthood); as a result, the bones and
muscles of the face, hands, and feet (the bones that arent affected
by sex steroids) become abnormally large, changing patients facial
features but not their height. The excessive production of GH in
adults usually comes from tumors of the pituitary or hypothalamus.
Nowadays however, this disorder is no longer common since the
GH-secreting tumors are now usually being diagnosed and treated
early enough that the condition never develops.
Diabetes mellitus commonly known as Diabetes, this condition is
a disorder of blood sugar regulation involving insulin (a hormone
thats produced in the pancreas, it is important in regulating
carbohydrate and fat metabolism in the body, and causes cells in
the liver, muscle, andfat tissuesto take upglucosefrom theblood,
storing it asglycogenin the liver and muscle.). There are two types
of diabetes:
a) Type 1 diabetes this is caused by a failure to produce enough
insulin, because of this, the patient only depends on daily doses
of insulin for survival, which is why it is also called
insulin-dependent diabetes. It normally develops during childhood
or adolescence, but adults can develop it as well. Generally it has
an autoimmune (failure of an organism to recognize a constituent as
part of itself, therefore causes immune responses against its own
cells and tissues) cause: the persons immune system destroys the
beta cells (cells that make and release insulin) of the
pancreas.
b) Type 2 diabetes also referred to as non-insulin-dependent
diabetes, unlike Type 1, insulin levels may be low, normal or quite
high, however, it is characterized by insulin resistance which
means cells fail to respond adequately to insulin even though it is
present.
Both types of Diabetes mellitus can damage the blood vessels and
nerves if not managed correctly. Chronic untreated diabetes is a
leading cause of blindness, kidney failure, heart disease and
stroke. People who are overweight and sedentary (no or irregular
physical activity) are more prone to develop this disease,
specifically Type 2 diabetes. The symptoms of having Diabetes are:
polyuria(frequent urination),polydipsia(increased thirst)
andpolyphagia(increased hunger), which may develop rapidly (weeks
or months) in Type 1 while in Type 2 they usually develop much
slower and may be subtle or absent. In addition, Type 2 diabetics
may experience having frequent infections, blurred vision, cuts
that heal very slow, and tingling in the feet or hands. To manage
their condition, Type 1 diabetics need daily injections of insulin
to stay alive, while Type 2 diabetics have numerous options
depending on their condition. Some may take insulin, but others
manage with drugs that stimulate insulin production. Others can be
managed without drugs through lifestyle changes like maintaining a
healthy weight, eating nutritious food, and regular, if not daily
exercising.
Goiter this disorder is of the Thyroid gland wherein the lack of
iodine, (which is required to produce active Thyroid hormones)
which results in an absent or abnormally low level of thyroxine,
makes the hypothalamus and pituitary to secrete large unchecked
quantities of Thyrotropin-releasing hormone (TRH) and
Thyroid-secreting hormone (TSH). And in doing so, the high TSH
levels stimulate the thyroid gland to grow to enormous size in an
effort to get the thyroid to make more hormone, which it cannot do
because it lacks iodine. As a result, the thyroid gland is
abnormally enlarged and causes a swelling of the neck or larynx
(voice-box) which we call a Goiter.
Note: the TRH is a hormone that stimulates the release of TSH by
the anterior pituitary. TSH on the other hand is a hormone which is
also secreted in the anterior pituitary gland but regulates the
endocrine function of the Thyroid gland. Thyroxene is the hormone
secreted by the thyroid gland.
Hypothyroidism: Underactive thyroid gland this refers to the
hyposecretion of thyroid hormones. In children, not enough
thyroxene production can slow body growth, alter brain development,
and delay the start of puberty. If not treated, the hypothyroidism
can lead to cretinism, a condition of mental retardation wherein
the child is left with short stature with an abnormally formed
skeletal structure. In adults, thyroxene deficiency can lead to
myxedema, a condition characterized by swelling under the skin,
lethargy (Fatigue), weight gain, low BMR (Basal-metabolic rate
refers to the amount of energy expended while at rest), and low
body temperature. This condition however, can be treated by means
of thyroxine pills which can increase thyroxene production.
Hyperthyroidism: Overactive thyroid gland this refers to the
hypersecretion of the thyroid hormones. Too much thyroxine
increases BMR and causes hyperactivity, nervousness, agitation, and
weight loss. Graves disease, an autoimmune disorder wherein the
persons own aintbodies stimulate the thyroid to produce too much
thyroxine, is the most common form of hyperthyroidism. Graves
disease is often associated by protruding eyes, a condition called
exopthalmia, caused by fluid accumulation behind the eyes.
Addisons disease: Too little cortisol and aldosterone this
condition is caused by the failure of the adrenal cortex to secrete
sufficient cortisol (a steroid hormone used in increasing blood
sugar) and aldosterone (a hormone that increases blood volume,
therefore, increasing blood pressure). The disease tends to develop
slowly with chronic symptoms of fatigue, weakness, abdominal pain,
weight loss, and characteristic bronzed skin color. It can be
successfully treated by replacing the missing hormones.
15
Cushings syndrome: Too much cortisol too much cortisol may
result in excessive production of glucose from glycogen and
protein, and retention of too much salt and water. Some of the
extra glucose is converted body fat, but only in certain areas of
the body like the face, abdomen, and the back of the neck.
Some symptoms include muscle weakness and fatigue, edema
(swelling due to too much fluid), and high blood pressure. It can
be caused by tumors of the adrenal gland or Adrenocorticotropic
hormone(ACTH a hormone produced in the anterior pituitary gland
that increases production and release of corticosteroids and
cortisol from the adrenal cortex)-secreting cells of the pituitary.
It can also be due to excessive use of cortisol or cortisol-like
drugs (cortisone, prednisone, dexamethasone, and others) to control
chronic inflammatory conditions such as allergies and arthritis.
Most Cushing's syndrome cases are caused by steroid medications,
consequently, most patients are effectively treated by carefully
tapering off (and eventually stopping) the medication that causes
the symptoms.Bibliography
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