Download ORGANIZATION AND CONTROL OF ENDOCRINE SYSTEM

ORGANIZATION AND CONTROL OF ENDOCRINE SYSTEM
ENDOCRINE SYSTEM
 uses chemical substances called hormones as a means of regulating and integrating
body functions.
 participates in the regulation of digestion, use, and storage of nutrients; growth and
development electrolyte and water metabolism; and reproductive functions.
 functions of the endocrine system are closely linked with those of the nervous
system and the immune system and functions of the immune system also are
closely linked with those of the endocrine system. The immune system responds to
foreign agents by means of chemical messengers (cytokines,
e.g., interleukins, interferons) and complex receptor mechanisms .The immune system also
is extensively regulated by hormones such as the adrenal cortico steroid hormones
ANATOMY OF ENDOCRINE SYSTEM
 The primary glands that make up the human endocrine system are the
hypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal body, and
reproductive glands—the ovary and testis.
 In addition, some nonendocrine organs are known to actively secrete hormones.
These include the brain, heart, lungs, kidneys, liver, thymus, skin, and placenta.
 Almost all body cells can either produce or convert hormones, and some secrete
hormones. For example, glucagon, a hormone that raises glucose levels in the blood
when the body needs extra energy, is made in the pancreas but also in the wall of
the gastrointestinal tract.
HORMONES
-are chemical messengers created by the body where they transfer information from one
set of cells to another to coordinate the functions of different parts of the body.
- specific messenger molecule synthesized and secreted by a group of specialized cells
called an endocrine gland.
PHEROMONES
- also communication chemicals, but are used to send signals to other members of the same
species.
ENDOCRINE GLAND
-ductless
- their secretions (hormones) are released directly into the bloodstream and travel to
elsewhere in the body to target organs, upon which they act.
EXOCRINE GLAND
-not part of the endocrine system that secrete products that are passed outside the body.
-Sweat glands, salivary glands, and digestive glands are examples of exocrine glands.
The roles of hormones in selecting target cells and delivering the hormonal message.
Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates
(www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission.
HORMONE RECEPTORS
-binding sites on the target cells
Each hormone’s shape is specific and can be recognized by the corresponding target cells.
Many hormones come in antagonistic pairs that have opposite effects on the target organs.
For example, insulin and glucagon have opposite effects on the liver’s control of blood
sugar level. Insulin lowers the blood sugar level by instructing the liver to take glucose out
of circulation and store it, while glucagon instructs the liver to release some of its stored
supply to raise the blood sugar level. Much hormonal regulation depends on feedback loops
to maintain balance and homeostasis.
CHARACTERISTICS OF HORMONES
A single hormone can exert various effects in different tissues or, conversely, a single
function can be regulated by several hormones.
■Hormones function as chemical messengers, moving through the blood to distant target
sites of action, or acting more locally as paracrine or autocrine messengers that incite more
local effects.
■Most hormones are present in body fluids at all times but in greater or lesser amounts,
depending on the needs of the body.
■Hormones exert their actions by interacting with high affinity receptors, which in turn are
linked to one or more effectors systems in the cell. Some hormone receptors are located on
the surface of the cell and act through second messenger mechanisms ,and others are
located in the cell, where they modulate the synthesis of enzymes, transport proteins,
or structural proteins
THREE GENERAL CLASSES OF HORMONES
These are classified by chemical structure, not function.
steroid hormones including prostaglandins which function especially in a variety
of female functions (aspirin inhibits synthesis of prostaglandins, some of which
cause “cramps”) and the sex hormones all of which are lipids made from cholesterol,
amino acid derivatives (like epinephrine) which are derived from amino acids,
especially tyrosine, and
peptide hormones (like insulin) which is the most numerous/diverse group of
hormones.
Local regulators
-hormones with target cells nearby or adjacent to the endocrine gland in question. For
example, neurotransmitters are secreted in the synapses of our nervous system and their
target cells are in the same synapses.
NONSTEROID HORMONES
- water soluble
-do not enter the cell but bind to plasma membrane receptors, generating a chemical signal
inside the target cell.
STEROID HORMONES
-pass through the plasma membrane and act in a two step process.
Steroid hormones bind, once inside the cell, to the nuclear membrane receptors, producing
an activated hormone-receptor complex. The activated hormone-receptor complex binds to
DNA and activates specific genes, increasing production of proteins.
Paracrine and Autocrine Actions-some hormones and hormone-like substances never
enter the blood-stream but instead act locally in the vicinity in which they are released.
Paracrine
- act locally on cells other than those that produced the hormone,
action of sex steroids on the ovary is a paracrine action.
Autocrine
- Hormones also can exert anautocrine
action on the cells from which they were produced. For example, the release of insulin from
pancreatic beta cells can inhibit its release from the same cells.
Juxtacrine
-refers to a mechanism whereby a cytokine that is em-bedded in, bound to, or associated
with the plasma membraneof one cell interacts with a specific receptor in a juxtaposed cell.
Eicosanoids and Retinoids- group of compounds that have a hormone-like action arethe
eicosanoids, which are derived from polyunsaturated fatty acids in the cell membrane.
EICOSANOIDS- arachidonic acid is the most important and abundant precursor of the
various eicosanoids.
- most important of the eicosanoids are the prostaglandins, leukotrienes, and
thromboxanes. (these fatty acid derivatives are produced by most body cells, are
rapidly cleared from the circulation, and are thought to act mainly by paracrine and
autocrine mechanisms.)
- Synthesis often is stimulated in response to hormones, and they serve as mediators of
hormone action. Retinoids ( e.g., retinoic acid) also are derived from fatty acids and
have an important role in regulating nuclear receptor action.
MAJOR HORMONES
Hormone Gland Origin Target Tissue Function
Adrenocorticotropic
Growth hormone
Pituitary
gland
(anterior)
Pituitary
gland
(anterior)
Adrenal cortex
Throughout body
Triggers secretion of
hydrocortisone from the
adrenal gland
Stimulates growth and
development
Follicle-stimulating
hormone
Pituitary
gland
(anterior)
Luteinizing hormone Pituitary
gland
(anterior)
Prolactin
Pituitary
gland
(anterior)
Thyroid-stimulating
Pituitary
hormone
gland
(anterior)
MelanocytePituitary
stimulating hormone gland
(anterior)
Antidiuretic hormone Pituitary
gland
(posterior)
Oxytocin
Pituitary
gland
(posterior)
Sex glands
Melatonin
Pineal gland
Calcitonin
Thyroid
gland
Unclear, although
possible target
sites are pigment
cells and sex
organs
Bones
Thyroid hormone
Thyroid
gland
Sex glands
Mammary glands
Thyroid gland
Melanin-producing Controls skin pigmentation
cells
Kidneys
Regulates water retention
and blood pressure
Uterus
Triggers contraction of the
uterus during labor
Stimulates milk letdown for
breast-feeding after
childbirth
May affect skin
pigmentation; may regulate
biorhythms (awake/sleep
patterns) and prevent jet
lag
Controls the level of calcium
in the blood by depositing it
in the bones
Increases the body's
metabolic rate; promotes
normal growth and
development
Regulates calcium level in
blood
Promotes the growth and
development of white blood
cells, helping the body fight
infection
Regulates sodium and
potassium levels in the
blood to control blood
pressure
Mammary glands
Throughout body
Parathyroid hormone Parathyroid
glands
Thymosin
Thymus
Bones, intestines,
and kidneys
White blood cells
Aldosterone
Kidneys
Adrenal
gland
Stimulates female egg
maturation and male sperm
production
Stimulates female ovulation
and male secretion of
testosterone
Stimulates milk production
in the breasts after
childbirth
Triggers secretion of
thyroid hormones
Hydrocortisone
Adrenal
gland
Throughout body
Epinephrine
Adrenal
gland
Muscles and blood
vessels
Norepinephrine
Adrenal
gland
Muscles and blood
vessels
Glucagon
Pancreas
Liver
Insulin
Pancreas
Throughout body
Estrogen
Ovaries
Female
reproductive
system
Progesterone
Ovaries
Testosterone
Testes
Mammary glands
Uterus
Throughout body
Erythropoietin
Kidney
Bone Marrow
Plays key role in stress
response; increases blood
glucose levels and mobilizes
fat stores; reduces
inflammatation
Increases blood pressure,
heart and metabolic rate,
and blood sugar levels;
dilates blood vessels. Also
released during exercise
Increases blood pressure
and heart rate; constricts
blood vessels
Stimulates the breakdown
of glycogen (stored
carbohydrate) into glucose
(blood sugar); regulates
glucose blood level
Regulates blood glucose
levels; increases storage of
glycogen; facilitates glucose
intake by body cells
Causes sexual development
and growth; maintains
proper functioning of
female reproductive system
Prepares uterus for
pregnancy
Causes sexual development
and growth spurt;
maintains proper
functioning of male
reproductive system
Produces red blood cells
Hormones Regulated by the Hypothalamic/Pituitary System
Hormone
Thyroid hormones T4, T3
Cortisol
Pituitary
Stimulating
Hormone
Thyroid-stimulating
hormone (TSH)
Adrenocorticotropin
hormone (ACTH)
Hypothalamic Releasing
Hormone
Thyrotropin-releasing
hormone (TRH)
Corticotropin-releasing factor
(CRF)
Estrogen or testosterone
Insulinlike growth factorI (IGF-I)
Follicle-stimulating
hormone (FSH),
luteinizing hormone
(LH)
Growth hormone
Hormones of the Anterior Pituitary
Hormone
Secreted by
Luteinizing hormonereleasing hormone (LHRH) or
gonadotropin-releasing
hormone (GnRH)
Growth hormone-releasing
hormone (GHRH)
Releasing Hormone
(Stimulates Secretion)
Human growth hormone
(hGh) or somatotropin
Somatotrophs
Growth hormone-releasing
hormone (GHRH), also known
as somatocrinin.
Thyroid-stimulating
hormone (TSH) or
thyrotropin
Thyrotrophs
Thyrotropin-releasing
hormone (TRH)
Follicle stimulating
Gonadotrophs
hormone (FSH)
Luteinizing hormone (LH) Gonadotrophs
Prolactin (PRL)
Lactotrophs
Adrenocorticotropic
Corticotrophs
hormone (ACTH) or
corticotropin
Melanocyte-simulating
Corticotrophs
hormone
(MSH)
Principal Actions of Anterior Pituitary Hormones
Hormone
Target Tissues
Human growth hormone
Liver
(hGh) or somatotropin
Gonadotropic-releasing
hormone (GnRH)
Gonadotropic-releasing
hormone (GnRH)
Prolactin-releasing hormone
(PRH); TRH.
Corticotropin-releasing
hormone (CRH).
Corticotropin-releasing
hormone (CRH).
Inhibiting
Hormone
(Suppresses
Secretion)
Growth
hormoneinhibiting
hormone
(GHIH), also
known as
somatostatin.
Growth
hormoneinhibiting
hormone
(GHIH).
Prolactininhibiting
hormone (PIH),
which is
dopamine.
Dopamine.
Principal Actions
Stimulates liver, muscle, cartilage,
bone and other tissues to
synthesize and secrete insulinlike
Thyroid-stimulating
hormone (TSH) or
thyrotrophin
Follicle stimulating
hormone (FSH)
Thyroid gland
Ovaries, Testes
Luteinizing hormone (LH) Ovaries, Testes
Prolactin (PRL)
Mammary glands
Adrenocorticotropic
hormone
Adrenal Cortex
Melanocyte-simulating
hormone (MSH)
Brain
Posterior Pituitary Hormones
Hormone
Target Tissues
growth factors (IGFs); IGFs
promote growth of body cells,
protein synthesis, tissue repair,
lipolysis, and elevation of blood
glucose concentration.
Stimulates synthesis and secretion
of thyroid hormones by thyroid
gland.
In females, initiates development of
oocytes and induces ovarian
secretion of estrogens. In males,
stimulates testes to produce sperm.
In females, stimulates secretion of
estrogens and progesterone,
ovulation and formation of corpus
luteum. In males, stimulates
interstitial cells in testes to develop
and produce testosterone.
Together with other hormones,
promotes milk secretion by the
mammary glands.
Stimulates secretion of
glucocorticoids (mainly cortisol) by
adrenal cortex.
Influence brain activity; when
present in excess, can cause
darkening of skin.
Control of Secretion
Oxytocin (OT)
Uterus, Mammary
glands
Neurosecretory cells of
hypothalamus secrete OT in
response to uterine distention
and stimulation of nipples.
Antidiuretic hormone
(ADH) or vasopressin
Kidneys,
Neurosecretory cells of
Sudoriferous (sweat) hypothalamus secrete ADH in
Principal
Actions
Stimulates
contraction of
smooth muscle
cells of uterus
during
childbirth;
stimulates
contraction of
myoepithelial
cells in
mammary
glands to cause
milk ejection.
Conserves
body water by
glands, Arterioles
response to elevated blood
osmotic pressure,
dehydration, loss of blood
osmotic pressure
dehydration, loss of blood
decreasing
urine volume;
decreases
water loss
tgrough
perspiration;
raises blood
pressure by
constricting
arterioles.
volume, pain or stress; low
blood osmotic pressure, high
blood volume, and alcohol
inhibit ADH secretion.
Thyroid Gland Hormones
Hormone
Source
Control of Secretion
Principal
Actions
T3 (triiodothyronine) and Thyroid follicle →
Secretion is increased by
Increase basal
T4 (thyroxine) or thyroid Follicular cells
thyrotropin-releasing
metabolic rate,
hormones from follicular
hormone (TRH), which
stimulate
cells
stimulates release of thyroid- synthesis of
stimulating hormone (TSH) in proteins,
response to low thyroid
increase use of
hormone levels, low metabolic glucose and
rate, cold, pregnancy, and high fatty acids for
ltitudes; TRH and TSH
ATP
secretion are inhibited in
production,
response to high thyroid
increase
hormone levels; high iodine
lipolysis,
level suppresses t3/t4
enhance
secretion.
cholesterol
excretion,
accelerate
body growth,
and contribute
to
development of
the nervous
system.
Calcitonin (CT) from
High blood Ca2+ levels
Lowers blood
Thyroid follicle →
parafollicular cells
stimulate secrewtion; low
levels of ionic
Parafollicular cells
accelerating
blood Ca2+ levels inhibit
calcium and
secretion.
phosphates by
inhibiting bone
resorption by
osteoclasts and
uptake of
calcium and
phosphates
into bone
matrix.
Parathyroid Gland Hormone
Hormone
Source
Control Secretion
Low blood Ca2+ levels
stimulate secretion. High
blood Ca2+ levels inhibit
secretion.
Principal
Actions
Increase blood
Ca2+ and Mg2+
levels and
decreases
blood
phosphate
level; increases
bone
resorption by
osteoclasts;
increases Ca2+
reabsorption
and phosphate
excretion by
kidneys; and
promotes
formation of
calcitriol
(active form of
vitamin D),
which
increases rate
of dietary Ca2+
and Mg2+
absorption.
Parathyroid hormone
(PTH)
Chief cells
Hormone and Source
Adrenal cortex hormones
Mineralocorticoids
(mainly aldosterone)
from zona glomerulosa
cells
Glucocorticoids (mainly
cortisol) from zona
fasciculate cells
Control of Secretion
Increased blood K+ level and
angiotensin II stimulate
secretion.
Principal Actions
Increase blood levels of Na+ and
water and decrease blood level of
K+.
ACTH stimulates release;
corticotropin-releasing hormone
(CRH) promotes ACTH secretion
in response to stress and low
blood levels of glucocorticoids.
Increase protein breakdown
(except in liver), stimulate
gluconeogenesis and lipolysis,
provide resistance to stress,
dampen inflammation, and depress
immune responses.
Androgens (mainly
dehydroepiandrosterone
or DHEA) from zona
reticularis cells
ACTH stimulates secretion.
Adrenal medulla
hormones
Epinephrine and
norepinephrine from
chromaffin cells
Sympathetic preganglionic
neurons release acetylcholine,
which stimulates secretion.
Pancreatic Hormones
Hormone and Source
Glucagon from alpha cells
of pancreatic islets
Insulin from beta cells of
pancreatic islets
Somatostatin from delta
cells of pancreatic islets
Pancreatic polypeptide
from F cells of pancreatic
islets
Control of Secretion
Decreased blood level of glucose,
exercise and mainly protein
meals stimulate secretion;
somatostatin and insulin inhibit
secretion.
Increased blood level of glucose,
acetylcholine (released by
parasympathetic vagus nerve
fibers), argentine and leucine
(two amino acids), glucagons,
GIP, hGh, and ACTH stimulate
secretion; somatostatin inhibits
secretion.
Pancreatic polypeptide inhibits
secretion.
Assist in early growth of axillary
and pubic hair in both sexes; in
females, contribute to libido and
are source of estrogens after
menopause.
Produce effects that enhance those
of the sympathetic division of the
autonomic nervous system (ANS)
during stress.
Principal Actions
Raises blood glucose level by
accelerating breakdown of
glycogen into glucose in liver
(glycogenolysis), converting other
nutrients into glucose in liver
(gluconeogenesis), and releasing
glucose into the blood.
Lowers blood glucose level by
accelerating transport of glucose
into cells, converting glucose into
glycogen (glycogenesis), and
decreasing glycogenolysis and
gluconeogenesis; also increase
lipogenesis and stimulates protein
synthesis.
Inhibits secretion of insulin and
glucagons and slows absorption of
nutrients from the gastrointestinal
tract.
Inhibits somatostatin secretion,
gallbladder contraction, and
secretion of pancreatic digestive
enzymes.
Meals containing protein, fasting,
exercise, and acute hypoglycemia
stimulate secretion; somatostatin
and elevated blood glucose level
inhibit secretion.
Hormone of the Ovaries and Testes
Hormone
Principal Actions
Ovarian hormones
Together with gonadotropic hormones of the
Estrogens and progesterone
anterior pituitary gland, regulate the female
reproductive cycle, regulate oogenesis, maintain
pregnancy, prepare the mammary glands for
lactation, and promote development and
maintenance of feminine secondary sex
characteristics.
Relaxin
Increase flexibility of pubic symphysis during
pregnancy and helps dilate uterine cervix
during labor and delivery.
Inhibin
Inhibits secretion of FSH from anterior
pituitary.
Testicular hormones
Stimulates descent of testes before birth,
Testosterone
regulates spermatogenesis, and promotes
development and maintenance of masculine
secondary sex characteristics.
Inhibin
Inhibits secretion of FSH from anterior
pituitary.
Hormones produced by organs and tissues that contain endocrine cells
Hormone
Principal Actions
Gastrointestinal tract
Promotes secretion of gastric juice and
Gastrin
increases motility of the stomach.
Glucose-dependent insulinotropic peptide
Stimulates release of insulin by pancreatic beta
(GIP)
cells.
Secretin
Stimulates secretion of pancreatic juice and bile.
Cholecystokinin (CCK)
Stimulates secretion of pancreatic juice,
regulates release of bile from the gallbladder,
and brings about a feeling of fullness after
eating.
Placenta
Stimulates the corpus luteum in the ovary to
Human chorionic gonadotropin (hCG)
continue the production of estrogens and
progesterone to maintain pregnancy.
Estrogens and progesterone
Maintain pregnancy and help prepare
mammary glands to secrete milk.
Human chorionic somatomammotropin (hCS)
Stimulates the development of the mammary
glands for lactation.
Kidneys
Increases rate of red blood cell formation.
Erythropoietin (EPO)
Calcitriol* (active form of vitamin D)
Aids in the absorption of dietary calcium and
phosphorous.
Heart
Decrease blood pressure.
Atrial natriuretic peptide (ANP)
Adipose tissue
Suppresses appetite and may have a permissive
Leptin
effect on activity of GnRH and gonadotropins
PARTS OF THE ENDOCRINE SYSTEM
Illustration of the endocrine system
Hypothalamus
- located in the lower central part of the brain.
- Part of the brain which is important in regulation of satiety, metabolism, and body
temperature.
- secretes hormones that stimulate or suppress the release of hormones in the
pituitary gland.
Releasing Hormones
- secreted into an artery (the hypophyseal portal system) that carries them directly
to the pituitary gland.
-it signals secretion of stimulating hormones.
Somatostatin
-it causes the pituitary gland to stop the release of growth hormone.
Pituitary Gland
-located at the base of the brain beneath the hypothalamus and is no larger than a pea.
-considered the most important part of the endocrine system because it produces
hormones that control many functions of other endocrine glands.
I.
ANTERIOR LOBE
Growth hormone: Stimulates growth of bone and tissue (growth
hormone deficiency in children results in growth failure. Growth
hormone deficiency in adults results in problems in maintaining proper
amounts of body fat and muscle and bone mass. It is also involved in
emotional well-being.)
Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to
produce thyroid hormones (A lack of thyroid hormones either because of
a defect in the pituitary or the thyroid itself is called hypothyroidism.)
Adrenocorticotropin hormone (ACTH): Stimulates the adrenal gland to
produce several related steroid hormones
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH):
Hormones that control sexual function and production of the sex steroids,
estrogen and progesterone in females or testosterone in males
Prolactin: Hormone that stimulates milk production in females
II.
POSTERIOR LOBE
Antidiuretic hormone (vasopressin): Controls water loss by the
kidneys
Oxytocin: Contracts the uterus during childbirth and stimulates milk
production
Thyroid Gland
-located in the lower front part of the neck.
-produces thyroid hormones that regulate the body's metabolism.
-plays a role in bone growth and development of the brain and nervous system in children.
Thyroid Hormone
- help maintain normal blood pressure, heart rate, digestion, muscle tone, and reproductive
functions.
Parathyroid Glands
- two pairs of small glands embedded in the surface of the thyroid gland, one pair on each
side.
- release parathyroid hormone.
PARATHROID HORMONE
-plays a role in regulating calcium levels in the blood and bone metabolism.
Adrenal Glands
- adrenal glands are triangular-shaped glands located on top of each kidney.
ADRENAL CORTEX
- outer part that produces hormones called corticosteroids, which regulate the
body's metabolism, the balance of salt and water in the body, the immune system,
and sexual function.
ADRENAL MEDULLA
- inner part that produces hormones called catecholamines (for example,
adrenaline).
These hormones help the body cope with physical and emotional stress by
increasing the heart rate and blood pressure.
Pineal Body/ Pineal Gland
- located in the middle of the brain.
- secretes a hormone called melatonin.
MELATONIN
- regulate the wake-sleep cycle of the body.
Reproductive Glands
- Main source of sex hormones.
MALES
- the testes, located in the scrotum, secrete hormones called androgens; the most
important of which is testosterone. These hormones affect many male
characteristics (for example, sexual development, growth of facial hair and pubic
hair) as well as sperm production.
FEMALES
- the ovaries, located on both sides of the uterus, produce estrogen and
progesterone as well as eggs. These hormones control the development of female
characteristics (for example, breast growth), and they are also involved in
reproductive functions (for example, menstruation, pregnancy).
Pancreas
- Elongated organ located toward the back of the abdomen behind the stomach.
- has digestive and hormonal functions.
EXOCRINE PANCREAS
- secretes digestive enzymes.
ENDOCRINE PANCREAS
- secretes hormones called insulin and glucagon.
These hormones regulate the level of glucose (sugar) in the blood.
HORMONE ACTION
 Hormone signals a cell by biding to specific receptors on or in the cell.
 “lock-and-key” mechanism (hormones will bind only to receptor molecules that fit them
exactly)
 Target cell (any cell with one or more receptors for a particular hormone)
 Each different hormone-receptor interaction produces different regulatory changes within
the target cell
 Different hormones may work together to enhance each other’s influence on a target cell.
o Synergism- combinations of hormones have a greater effect on the target cell than the
sum of the effects that each would have if acting alone
o Permissiveness- it occurs when a small amount of one hormone allows a second
hormone to have its full effect on a target cell; the first hormone permits the full action of
the second hormone
o Antagonism- seen as the common type of combined action of hormones; one hormone
produces the opposite effect of another hormone; it give signals to the cell when to
increase or decrease a certain cellular process
Mechanism of Steroid Hormone Action
Steroid hormones are lipids and thus are not very soluble in blood plasma, which is mostly
water. Instead of travelling in the plasma as free molecules, they attach to soluble plasma
proteins.
A steroid hormone molecule dissociates from its carrier before approaching the target cell.
Because steroid hormones are lipid-soluble and thus can pass into cells easily, it is not
surprising that their receptors are normally found inside the cell rather than on the surface
of the plasma membrane.
After
a
steroid
hormone
molecule has diffused into its
target cell, it passes into the
nucleus where it binds to a
mobile receptor molecule to form
a hormone-receptor complex.
Some hormones must be
activated by enzymes before
they can bind to their receptors.
Because
steroid
hormone
receptors are not attached to the
plasma membrane, but seem to
move freely in the nucleoplasm,
this model of hormone action
has been called the mobilereceptor hypothesis.
Once formed, the hormone-receptor complex activates a certain gene sequence to begin
transcription of messenger RNA (mRNA) molecules.
The newly formed mRNA molecule then move out of the nucleus into the cytosol, where they
associate with ribosomes and begin synthesizing protein molecules.
The new protein molecules synthesized by the target cell would not have been made if not
for the arrival of the steroid hormone molecule. Steroid hormones regulate cells by
regulating their production of certain critical proteins.
This mechanism of steroid hormone action implies several things about the effects of these
hormones. For one thing, the more hormone-receptor complexes formed, the more new
protein molecule are formed, and thus the greater the magnitude of regulatory effect.
Mechanisms of Nonsteroid Hormone Action
Nonsteroid hormones typically operate according to a mechanism originally called the
second messenger hypothesis. According to this concept, also called fixed-membrane-receptor
hypothesis, a nonsteroid hormone molecule acts as a “first messenger,” delivering its chemical
message to fixed receptors in the target cell’s plasma membrane.
The second messenger mechanism produces target cell effects that differ from steroid
hormone effects in several important way. First, the cascade of reactions produced in the
second messenger mechanism
greatly amplifies the effects of
the hormone. Thus the effects of
many nonsteroid hormones are
disproportionally great when
compared to the amount of
hormone present. Recall that
steroid hormones produce
effects in proportion to the
amount of hormone present.
Also, the second messenger
mechanism operates much
more quickly than steroid
mechanism. Many nonsteroid
hormones produce their full
effects within seconds or
minutes of initial binding to the
target cell receptors—not the
hours or days sometimes seen with steroid hormones.
In the figure, a nonsteroid hormone binds to a fixed receptor in the plasma membrane of
the target cell. The hormone-receptor complex activates the protein and the activated protein
reacts with a certain nucleotide, which in turn activates the membrane-bound enzyme. The
activated membrane-bound enzyme removes phosphates from ATP, converting it to cyclic
adenosine monophosphate (cAMP). cAMP activates or inactivates an enzyme that will activate
intracellular enzyme. These activated enzymes then influence specific cellular reactions, such
as glycogen breakdown, thus producing the target cell’s response to the hormone
The nuclear receptor mechanism
 Not all steroid hormones operate according to the second messenger.
 Thyroxine (T4) and triiodothronine (T3) are small iodinated amino acids that apparently
enter their target cells and bind to receptors already associated with a DNA molecule
within the nucleus of the target cell. Formation of a hormone-receptor complex triggers
transcription of mRNA and the synthesis of new enzymes in a manner similar to the steroid
mechanism.
REGULATION OF HORMONE SECRETION
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


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It is usually part of a negative feedback loop
Responses that result from the operation of feedback loops within the endocrine system
are called endocrine reflexes.
The simplest mechanism operates when endocrine cell is sensitive to the physiological
changes produced by its target cells
Another mechanism that may influence the secretion of hormones by a gland is input from
the nervous system
Although the operation of long feedback loops tend to minimize wide fluctuations in
secretion rates, the output of several hormones typically rises and falls dramatically within
a short period. For example, the concentration of insulin—a hormone that can correct a
rise in blood glucose concentration—increase to a high level just after a meal high in
carbohydrates. The level of insulin decreases only after the blood glucose concentration
returns to its set point value. Likewise, threatening stimuli can cause a sudden dramatic
increase in the secretion of epinephrine from the adrenal medulla as part of the fight-orflight response.
DISORDERS AND DISEASES OF ENDOCRINE SYSTEM
Hypersecretion- production of too much hormone.
Gigantism- abnormal rapid rate of skeletal growth.
Acromegaly-a condition in w/c cartilage is still left in the skeleton continuous
to form new bone.
-result in hypersecretion after skeletal fusion.
- may result from pituitary tumor, abnormally onset of puberty.
Hyposecretion- production of too little hormone.
Pituitary Dwarfism- stunted body growth.
-may result to disruption of reproduction, kidney function, overall
metabolism.

ANTIDIURETIC Hormone(ADH) Abnormalities
Diabetes insipidus- hyposectretion of Antidiuretic hormone(ADH).
-abnormal production of large amounts of urine.

THYROID Hormone Abnormalities
Graves diseases- hypersecretion of thyroid hormone w/c is thought to be an
autoimmune condition.
-leads to weight loss, nervousness, increased in heart rate, and
exophthalmos- protrusion of the eyeballs resulting from edema of tissue at
the back of the eye socket.
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
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Cretinism- hyposecretion of thyroid hormone during growth years.
-characterized by a low metabolic rate, retarded growth and sexual
development, and possibly mental retardation, decreased metabolic weight,
loss of hair, yellow dullness of the skin, and myxedema-swelling(edema) and
firmness of the skin caused by accumulation of mucopolysaccharides in the
skin.
PARATHYROID Hormone Abnormalities
Hyperthyroidism- leads to increase in blood calcium levels and possible
development of osteoporosis and kidney stones due to elevation of
parathyroid hormone.
Hypocalcemia- too much tissue is removed that results to drop in PTH below
normal limits.
-cryopreservation- deep freezing, of the removed tissue of 1 year.
ADRENAL CORTICAL Hormone Abnormalities
Aldosteronism- hypersecretion of aldosterone that leads to increased water
retention and muscle weakness resulting from K ion loss.
Virilizing tumors-tumor of the adrenal cortex due to hypersection of
androgens. Also it increase the blood level of male hormones.
Cushing syndrome- the hypersecretion of cortisol from the adrenal cortex
-also had the characteristics of moon face and thin, reddened skin.
DIABETES MELLITUS
-most common endocrine disorders.
-result when the pancreatic islets secrete too little insulin, resulting in increased
levels of blood glucose.
Insulin resistance- the inability of fat, muscle, and other cells to respond
normally to insulin and permit the entry of the sugar.
Insulin insensitivity- the opposite of insulin resistance.
Hyperglycemia- the chronic elevation of blood glucose levels.
Glycosuria- spilling over of sugar into the urine.
Polyuria- increased urine production.
Polydipsia- excessive and ongoing thirst.
Polyphagia-intense and continuous hunger.
Diabetic ketoacidosis- accumulation of ketone bodies in the blood.
Types of Diabetes Mellitus
a. Type 1(juvenile-onset diabetes)- usually strikes before 30 years of age.
- Also called the insulin-dependent diabetes mellitus(IDDM).
An autoimmune disease usually triggered by some type of viral infection in
genetically susceptible individuals
b. Type 2(non-insulin-dependent diabetes mellitus)
- Most common form of diseases.
- Often occurs after age 40 years.
- A specific gene defect.
-
THYROID DISORDERS:
Euthyroidism- the thyroid gland is functioning normally.
Hyperthyroidism- increased secretion of the gland’s hormone.
Hypothyroidism- decreased section of the gland’s hormone.
GOITER
a. Endemic goiter- nutritional iodine deficiency.
b. Sporadic goiter- not restricted to any geographical area. Major causes include
the following:
- Genetic defects resulting in faulty iodine metabolism
- Ingestion of large amounts of goitrogens such as cabbage soybeans and
spinach.
- Ingestions of medicinal goitrogens such as glocorticoids, dopamine, lithium.
HYPOTHYROIDISM
-a deficiency of TH resulting in slowed body metabolism,
Decrease heat production and decreased oxygen consumption by the tissues.
Primary hypothyroidism
-TH levels are low and TSH levels are elevated.
*Hashimoto’s disease- most common form of primary-autoimmune
hypothyroidism.
Secondary hypothyroidism
-insufficient stimulation of a normal thyroid gland, results decreased
TSH levels.
Tertiary or central hypothyroidism
-develops if the hypothalamus cannot produce TRH and TSH.
Subclinical hypothyroidism
-diagnosed with an elevated TSH level but a normal to low normal T4
level.
HYPERTHYROIDISM
-Excessive secretion of TH.
Thyroid storm(Thyrotoxicosis)
-potentially fatal acute episode of overactivity characterized by high
fever, severe tachycardia , delirium, dehydration, and extreme
irritability.
*Thyroidectomy-removal of the thyroid gland; may be total or partial.
THYROIDITIS
-inflammation of the thyroid gland.
 Hope this movie helps you more understand abput endocrine system.
http://www.youtube.com/watch?v=-S_vQZDH9hY
http://www.youtube.com/watch?v=D6mZaFG-W4A&feature=related
SOURCES:
INTERNET
 http://biology.clc.uc.edu/courses/bio105/endocrin.htm
 http://www.emedicinehealth.com/anatomy_of_the_endocrine_system/page12_em.h
tm#authors_and_editors
 http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookendocr.html
 https://www.healthtap.com/#topics/endocrine-system-trivia
 http://www.scribd.com/doc/25408619/PATHO-CH30-Organization-and-Controlof-the-Endocrine-System-Porth
 http://t1.gstatic.com/images?q=tbn:ANd9GcQjaeNC1cU6E7Hhj2ULQJuG7p173rJWu
bMQ-hR7z0Whi9f3_iiCow
 http://t2.gstatic.com/images?q=tbn:ANd9GcTmIGtvPswIMmKUwb1eDEKNGaGPCuLqqOG4YPoXiRAxSDJdQw-CA
 (n.d.). Retrieved from http://www.thepepproject.net/
 (n.d.). Retrieved from http://www.google.com/
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 (n.d). Retrieved from
http://www.youtube.com/results?search_query=ENDOCRINE+SYSTEM&oq=ENDO
CRINE+SYSTEM&gs_l=youtube.3..0l10.54286.55157.0.55677.14.6.0.0.0.2.403.1161.
1j2j2j0j1.6.0...0.0...1ac.1.hcuMCLMWh84
 Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights
reserved.
BOOKS
 Thibodeau, G. A., & Patto, K. T. (2003). Anatomy and Physiology (5th editon ed.).
Mosby.
 Black, J. M., & Hawks, J. H. MEDICAL-SURGICAL NURSING (18TH ed.).
 Thibodeau, G. A., & Patton, K. T. (2003). Anatomy and Physiology (5th editon ed.).
Mosby.
 Thibodeau, & Patton. Anatomy and Physiology (18th ed.).
.