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Endocrine System
The endocrine system interacts with the nervous system to coordinate and integrate the
activity of cells.
Endocrine
Nervous
Work together to maintain homeostasis
Involves the binding of chemical signaling molecule to receptor on target cell
Consists of endocrine cells and tissues
Consists of brain, spinal cord, nerves and sense
organs
Use hormones as chemical signals
Use neurotransmitters as chemical signals
Hormones travel through the bloodstream
Neurotransmitters released at synapse with the
effector
Have a “lag period” of seconds or even days
Effectors respond within milliseconds
Effects may be prolonged
Response only prolonged if stimulus continues to
be applied
A hormonal stimulus typically produces one or more of the following changes:
1. Alters membrane permeability or membrane potential, or both, by opening or closing ion
channels
2. Stimulates synthesis of proteins or regulatory molecules such as enzymes within the cell
3. Activates or deactivates enzymes
4. Induces secretory activity
5. Stimulates mitosis
Most hormones are amino acid based and according to their size may be amines, peptides, polypeptides
or proteins; other hormones are steroids (recall that steroids are lipids). This affects the ability of the
hormone to enter the target cell. Steroids can pass through the cell membrane (a lipid can pass
through a lipid) so the receptors for the steroids are intracellular; receptors for most of the amino acid
based hormones are on the cell membrane (the exceptions are T3 and T4, which are amines, but the
receptor is intracellular). The best way to remember which hormones are steroids and which are amino
acid based is to memorize the shortest list. Hormones produced by the adrenal cortex and the gonads
are steroids; the rest are amino acid based hormones.
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Many amino acid derived
hormones exert their signaling
effects through intracellular
second messengers (such as cyclic
AMP or Ca++). The receptor for
insulin is a tyrosine kinase enzyme
that is activated by
autophosphorylation.
The steroid hormones (and thyroid hormone) diffuse into their target
cells where they bind to and activate an intracellular receptor. The
activated receptor-hormone complex then makes its way to the DNA
where is serves as a transcription factor.
The synthesis and release of most hormones are regulated by some
type of negative feedback system. Many functions of a living thing
depend on negative feedback, not just hormone action. The negative
feedback mechanism you are probably most familiar with is
thermoregulation. You should become familiar with some examples
of negative feedback in the endocrine system. Regulation of blood
glucose levels is a good example, since imbalances in blood glucose can
lead to serious disorders.
Examples of negative feedback mechanisms are on pages
through . We will look at three of them in detail.
2
In many cases positive feedback
leads to disorder, but in the
production of oxytocin by the
posterior pituitary it is ormal.
Pituitary-Hypothalamic Relationships
In humans, the pituitary gland has two major lobes- one is neural tissue and one is
glandular. The posterior pituitary is composed of glial-like cells and nerve fibers; it
releases neurohormones which are actually produced by the hypothalamus.
The anterior pituitary is glandular tissue and releases several hormones, most are
tropic.
**Tropic hormones act on other
endocrine glands- for example
TSH stimulates the thyroid
gland.
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Endocrine Gland Hormone
Chemical Class
Anterior
Pituitary
Growth Hormone
(GH)
protein
Thyroid Stimulating
Hormone (TSH)
glycoprotein
Adrenocorticotropic
Hormone (ACTH)
polypeptide
Follicle-stimulating
Hormone (FSH)
glycoprotein
Luteinizing Hormone
(LH)
glycoprotein
Prolactin (PRL)
protein
Target Organ and
Effects
Liver, muscle, bone
cartilage-acts as
anabolic hormone;
stimulates somatic
growth; mobilizes fat;
spares glucose
Thyroid glandstimulates thyroid
gland to release thyroid
hormones
Adrenal cortexpromotes release of
glucocorticoids and
androgens
Ovaries and testes- in
females, stimulates
ovarian follicle
maturation and
estrogen production; n
males, stimulates sperm
production
Ovaries and testes- in
females, triggers
ovulation and
stimulates ovarian
production of estrogen
and progesterone; in
males, promotes
testosterone
production
Mammary glandspromotes lactation
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Endocrine Gland Hormone
Chemical Class
Posterior
Pituitary
(produced in
hypothalamus,
released by
posterior
pituitary)
Oxytocin
peptide
Antidiuretic hormone
(ADH) aka
Vasopressin
Thyroxine (T4) and
triiodothyronine
(T3)- usually just
referred to as thyroid
hormone (TH)
peptide
Calcitonin- #does not
appear to play an
important role in
calcium homeostasis
in humans
Polypeptide
Parathyroid Hormone
(PTH) THE SINGLE
Protein
Thyroid Gland
Parathyroid
Gland
MOST IMPORTANT
HORMONE
CONTROLLING
CALCIUM BALANCE
OF THE BLOOD
Peptide- but
uses an
intracellular
receptor
Target Organ and
Effects
Uterus-stimulates
uterine contractions,
initiates labor
Breast- initiates milk
ejection
Kidneys- stimulates
kidney tubule cells to
reabsorb water
Affects virtually every
cell in the body and
serves as the body’s
major metabolic
hormone-increases
basal metabolic rate and
body heat production;
plays an important role
in regulating BP;
important in regulating
tissue growth and
development; critical
for normal skeletal and
nervous system
development
Bones- stimulates bone
forming cells and
inhibits bone
breakdown; in this way
it decreases blood Ca++
levels
Bone- stimulates
breakdown of bone;
Kidneys-enhances
reabsorption of Ca++;
Also necessary for the
activation of Vitamin D
which allows Ca++
absorption from food
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Endocrine
Gland
Adrenal Cortex
Adrenal
medulla
Hormone
Mineralcorticoids,
such as Aldosterone
Chemical
Class
Steroid
Glucocorticoids,
such as Cortisol and
Cortisone
Steroid
Gonadocorticoids
such as Androgens
(male sex
hormones)
Steroid
Epinephrine and
norepinephrine
amines
Target organ and Effects
Kidneys- increase blood
levels of Na+ and decrease
blood levels of K+; since
water reabsorption
accompanies sodium
retention, blood volume and
blood pressure rise
Body cells-promote
gluconeogenesis and
hyperglycemia; mobilize fats
for energy metabolism;
stimulate protein catabolism;
assist body to resist stressors;
depress inflammatory and
immune responses
Insignificant effects in males;
responsible for female libido;
development of pubic and
axillary hair in females;
source of estrogen after
menopause
“short term stress response”“fight or flight”; increased
heart rate, increased BP, liver
converts glycogen to
glucose, dilation of
bronchioles, changes in
blood flow patterns,
increased metabolic rate
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Endocrine
Gland
Pineal Gland
Hormone
Pancreas
*the pancreas is
both an
endocrine and
exocrine glandthe endocrine
part is called
the pancreatic
islets (islets of
Langerhans)
Insulin
*produced by beta
cells within the
pancreatic islets
Protein
Glucagon
*produced by alpha
cells within the
pancreatic islets
Polypeptide
Melatonin
Chemical
Class
Amine
Target Organ and Effects
Levels rise and fall in a
diurnal cycle; peak levels
occur at night and make us
drowsy, lowest levels occur
around noon; in some
animals, mating behavior and
gonadal size vary with
changes in amounts of
melatonin secreted; in
humans, melatonin may
affect the timing of puberty
Acts on most body cells- it
enhances membrane
transport of glucose in many
types of cells; insulin triggers
enzymatic activities that
catalyze the oxidation of
glucose for ATP production,
join glucose molecules
together to form glycogen,
convert glucose to fat.
Overall, insulin lowers blood
levels of glucose
Liver- breakdown of
glycogen to glucose;
synthesis of glucose from
lactic acid and other
noncarbohydrate molecules
(gluconeogenesis), release of
glucose to the blood by liver
cells, causing blood glucose
levels to rise
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Endocrine
Gland
Ovaryspecifically
the follicles
and the
corpus
luteum
Hormone
Chemical Class
Target organ and effects
Estrogen-the
release of
estrogen is
stimulated by
FSH and LH
Steroid
Stimulates growth & maturation
of reproductive organs & breasts
at puberty & maintain their adult
size & function; promotes
proliferative phase of the uterine
cycle. Promotes oogenesis &
ovulation; During pregnancy
stimulates growth of the uterus
& enlargement of the mammary
glands
Cooperates with estrogen in
stimulating growth of the
breasts; promotes the secretory
phase of the uterine cycle. During
pregnancy quiets the
myometrium and acts with
estrogen to cause mammary
glands to achieve their mature
milk producing state.
Stimulates formation of male
reproductive ducts, glands and
external genitalia; promotes
descent of the testes. Stimulates
growth and maturation of the
internal and external genitalia at
puberty. Required for normal
spermatogenesis. Stimulates the
growth spurt at puberty,
promotes increases skeletal and
muscle mass during adolescence.
Promotes growth of the larynx
and vocal cords. Enhances hair
growth, especially on the face,
axillae, genital region and chest.
Responsible for libido in males.
ProgesteroneSteroid
the release of
progesterone is
stimulated by LH
Testesspecifically
interstitial
cells
Testosterone
Steroid
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Examples of negative
feedback in the endocrine
system
Regulation of blood glucose levels-
Regulation of blood Ca++ levels-
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Regulation of plasma volume (and blood pressure)-
Which of the following is NOT a steroid hormone?
a. testosterone
b. aldosterone
c. progesterone
d. insulin
e. estrogen
Tropic hormones from the anterior pituitary directly affect the release of:
a. PTH
b. glucagon c. epinephrine
d. calcitonin
e. thyroxine
All of the following endocrine structures are controlled by a tropic hormone from the
anterior pituitary except:
a. adrenal cortex
c. testes
e. ovaries
b. thyroid gland
d. pancreatic islet cells
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Alpha and beta cells are commonly found in the:
a. endocrine control center
c. pituitary gland
b. hypothalamus
d. liver
ADH’s main target is the:
a. adrenal gland
b. posterior pituitary
c. kidneys
d. bladder
e. pancreas
e. anterior pituitary
In mammals, a decrease in body temperature results in which of the following
responses?
a. Release of thyroxine decreases the rate of metabolism.
b. Blood vessels close to the surface of the skin constrict.
c. Increased secretion of epinephrine restricts the amount of sugar released
into the circulatory system.
d. The adrenal glands increase the release of acetylcholine into the circulatory
system.
When a person exercises strenuously, all of the following occur EXCEPT:
A)
Glucose decreases.
C)
Lactic acid increases.
B)
ADP increases.
D)
Glycogen increases
Which of the following is LEAST likely to be associated with diabetes mellitus?
A)
Insulin receptors are insensitive to insulin.
B)
Urinalysis indicates a high concentration of sugar in urine.
C)
Pancreatic islet cells are destroyed.
D)
Liver cells absorb sugar from the blood at a rate that is greater than normal.
Uptake and conversion of glucose molecules to glycogen, or the breakdown of
glycogen to glucose molecules is controlled by hormones that target liver cells.
Which best describes this antagonistic hormonal interaction?
a. Insulin promotes glucose uptake by liver cells and glucagon promotes glycogen
breakdown.
b. Glucagon promotes glucose uptake by liver cells and insulin promotes glycogen
breakdown.
c. Insulin promotes glycogen uptake by liver cells and glucagon promotes glucose
breakdown.
d. Glucagon promotes glycogen uptake by liver ells and insulin promotes glucose
breakdown.
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The secretion of hormone A causes an increase in activity X within an organism. If this
mechanism works by positive feedback, which of the following statements represents
that fact?
a. An increase in activity X produces an increase in hormone A. An increase in
hormone A produces an increase in activity X.
b. An increase in activity X produces an increase in hormone A. An increase in
hormone A produces a decrease in activity X.
c. A decrease in activity X produces an increase in hormone A. A decrease in
hormone A produces an increase in activity X.
d. A increase in hormone A produces a increase in activity X. Activity X has no effect
on production of hormone A.
The endocrine system and nervous system work together to maintain
homeostasis. This is accomplished primarily by negative feedback. Which
of the following is an example of negative feedback in the endocrine system?
a. At the onset of labor, stretch on the uterine wall stimulates the posterior pituitary
to release oxytocin, which stimulates further contraction of the smooth muscle of the
uterus
b. As body temperature decreases in mammals, hormones of the hypothalamus exert
an inhibitory effect on sweat glands, reducing the amount of heat lost by evaporation
c. As blood glucose levels rise after a meal, alpha cells of the pancreas release insulin,
which promotes the breakdown of glycogen in liver cells
d. A decrease in blood calcium levels triggers the production of PTH; PTH targets
osteoclasts in the bone which break down bone, releasing calcium and phosphates
into the blood stream
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