Download 23.2 How Do Animal Hormones Work?

Chapter 23
Chemical Control of
the Animal Body:
The Endocrine
System
Lectures by
Gregory Ahearn
University of North Florida
Copyright © 2009 Pearson Education, Inc..
23.1 How Do Animal Cells Communicate?
 Cells communicate by releasing chemical
messenger molecules that affect other cells,
either nearby or far away.
• A messenger molecule alters the physiology of
a cell by binding to receptors, which are
specialized proteins located on the surface of
the cell.
• When a messenger molecule binds to a
receptor, the recipient cell responds in a way
that is determined by the messenger, the
receptor, and the type of cell.
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23.1 How Do Animal Cells Communicate?
 Responses to messenger molecules can be
varied.
•
•
•
•
Muscle contraction
Electrical activity of nerve cells
Secretion of milk in women
Active transport of salt by kidney cells
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23.1 How Do Animal Cells Communicate?
 Almost all animals have two large,
specialized organ systems in which
chemical communication is especially
important.
• The endocrine system
• The nervous system
 The endocrine system is an integrated
group of secretory structures, called glands,
that regulate growth, development,
metabolism, and reproduction.
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23.2 How Do Animal Hormones Work?
 Hormones are chemical messengers,
secreted by specialized cells of endocrine
glands, that initiate changes in other cells.
• Hormones travel from the tissues where they
are synthesized to target cells via the blood.
• Hormones only have an effect in target cells of
specific organs or tissues where appropriate
receptors for the hormones are present.
• Each cell, therefore, can respond to some
hormones but not to others.
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23.2 How Do Animal Hormones Work?
 Hormone release, distribution, and reception
Endocrine cells
release hormone
The hormone enters the
blood and is carried
throughout the body
The hormone leaves
the capillaries and
diffuses to all tissues
through the extracellular
fluid
(extracellular
fluid)
capillary
biceps
The hormone affects cells
bearing receptors to which
the hormone can bind
uterus
The hormone cannot affect
cells that only bear receptors to
which the hormone cannot bind
Fig. 23-1
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23.2 How Do Animal Hormones Work?
 Many different molecules serve as
hormones.
• There are three classes of hormones:
• Peptide hormones: chains of amino acids
• Amino acid-derived hormones: modified
amino acids
• Steroid hormones: synthesized from
cholesterol
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23.2 How Do Animal Hormones Work?
 Hormones act by binding to receptors in or
on target cells.
• Hormone receptors can be on the plasma
membrane or within the nucleus of target
cells.
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23.2 How Do Animal Hormones Work?
 Some hormones bind to receptors on the
surfaces of target cells.
• Peptide and amino acid-derived hormones
cannot penetrate plasma membranes to
initiate a series of reactions in the target cell.
• Instead, they bind to receptors on the target
cell’s plasma membrane.
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23.2 How Do Animal Hormones Work?
 Peptide and amino-acid based hormones
• Step 1: Hormone–receptor binding stimulates
production of a second messenger molecule
in the cell.
• Step 2: The second messenger transfers the
signal from the first messenger—the
hormone—to other molecules within the cell.
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23.2 How Do Animal Hormones Work?
 Peptide and amino acid-derived hormones
(continued)
• Step 3: The second messenger, such as
adenosine monophosphate (cyclic AMP),
initiates a chain of biochemical reactions.
• Step 4: The target cell synthesizes or secretes
substances.
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23.2 How Do Animal Hormones Work?
 Actions of peptide and amino acid–derived
hormones on target cells
peptide or
amino acid-derived
hormone
(1st messenger)
The hormone
binds to a receptor
on the plasma
membrane of a
target cell
Hormone–receptor binding
activates an enzyme that catalyzes
the synthesis of a second messenge
such as cyclic AMP
(cytoplasm)
cyclic AMPsynthesizing
enzyme
ATP
(extracellular
fluid)
receptor
active
enzyme
cyclic AMP
(2nd messenger)
product
The activated enzymes
catalyze specific reactions
plasma membrane
inactive
enzyme
reactant
The second
messenger activates
other enzymes
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nuclear
envelope
(nucleus)
Fig. 23-2
23.2 How Do Animal Hormones Work?
PLAY
Animation—Peptide Hormones
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23.2 How Do Animal Hormones Work?
 Some hormones bind to receptors inside
target cells.
• Steroid hormones are lipid soluble, so they
pass through plasma membranes and initiate
a series of reactions inside cells.
• Step 1: Once inside, these hormones bind
to receptors inside target cells.
• Step 2: These receptors are either in the
nucleus or move into the nucleus after
binding to the hormone.
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23.2 How Do Animal Hormones Work?
 Steroid hormones (continued)
• Step 3: The hormone–receptor complex binds
to the DNA of the promoter region of specific
genes.
• Step 4: Transcription of mRNA is stimulated.
• Step 5: The mRNA travels to the cytoplasm
and directs protein synthesis.
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23.2 How Do Animal Hormones Work?
 Steroid hormone action on target cells
steroid hormone
(extracellular
fluid)
The hormone binds to a
receptor in the nucleus or to
a receptor in the cytoplasm
that carries it into the nucleus
The hormone–receptor
complex binds to DNA and
causes RNA polymerase to
bind to a nearby promoter
site for a specific gene
A steroid hormone
diffuses through the
plasma membrane
DNA
plasma
membrane
hormone receptor
ribosome
RNA polymerase
The mRNA leaves the
nucleus, then attaches to a
ribosome and directs the
synthesis of a specific protein
product
mRNA
RNA polymerase catalyzes
the transcription of DNA into
messenger RNA (mRNA)
gene
new protein
nuclear
envelope
(cytoplasm)
(nucleus)
Fig. 23-3
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23.2 How Do Animal Hormones Work?
PLAY
Animation—Steroid Hormones
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23.2 How Do Animal Hormones Work?
 Hormone release is regulated by feedback
mechanisms.
• The release of most hormones is controlled by
negative feedback.
• This is a response to a change that tends to
counteract the change and to restore the
system to its original condition.
• Excessive perspiration is followed by pituitary
release of antidiuretic hormone, which causes
your kidneys to reabsorb water to restore your
blood volume.
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23.2 How Do Animal Hormones Work?
 Hormone release is regulated by feedback
mechanisms (continued).
• In a few cases, hormone release is controlled
by positive feedback, in which the response to
a change enhances the change.
• During birth, the baby’s pressure on the
mother’s cervix causes her brain to release
oxytocin, which stimulates contractions of the
uterus, pushing the baby harder against the
cervix.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 What are the major endocrine glands and
organs?
•
•
•
•
•
The hypothalamus–pituitary complex
The thyroid gland
The pancreas
The sex organs
The adrenal glands
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Hypothalamus
ADH, oxytocin, and regulatory
hormones for the anterior
pituitary
Pineal gland
melatonin
Pituitary gland
anterior pituitary:
Parathyroid glands
(on the posterior surface
of the thyroid gland)
parathyroid hormone
ACTH, TSH, GH, PRL, FSH, LH
posterior pituitary:
oxytocin and ADH
Thyroid gland
thyroxine, calcitonin
Heart
atrial natriuretic
peptide
Thymus gland
thymosins
Kidneys
erythropoietin
Digestive tract
several hormones
(see Chapter 21)
Adrenal glands (one on
each kidney)
medulla:
epinephrine, norepinephrine
cortex:
Fat
leptin
glucocorticoids (cortisol),
mineralocorticoids
(aldosterone), testosterone
Gonads
testes (male):
Pancreas islet cells
insulin, glucagon
androgens,
especially
testosterone
ovaries
(female):
testis
estrogens,
progesterone
ovary
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Fig. 23-4
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Hormones of the hypothalamus and pituitary
gland regulate many functions throughout the
body.
• The hypothalamus and pituitary gland coordinate the
action of many key hormonal system.
• The hypothalamus is a part of the brain that contains
clusters of specialized nerve cells, called
neurosecretory cells.
• Neurosecretory cells synthesize peptide hormones,
store them, and release them when stimulated.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Hormones of the hypothalamus and pituitary
gland regulate many functions throughout
the body (continued).
• The pituitary gland is a pea-sized gland that
dangles from the hypothalamus by a stalk.
• It consists of two parts: the anterior pituitary
and the posterior pituitary.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The hypothalamus/pituitary system
hypothalamus
Neurosecretory cells of
the hypothalamus produce
oxytocin and ADH
Neurosecretory cells
of the hypothalamus
produce releasing and
inhibiting hormones
Releasing or inhibiting
hormones (green circles) are
secreted into capillaries feeding
the anterior lobe of the pituitary
Oxytocin and ADH
(blue triangles are
secreted into the blood
via capillaries in the
posterior pituitary
blood flow
pituitary
(anterior lobe)
endocrine cell
pituitary
(posterior lobe)
capillary
bed
capillary bed
Endocrine cells of the
anterior pituitary secrete
hormones (red squares)
in response to releasing
hormones
blood
flow
Fig. 23-5
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
PLAY
Animation—Hypothalamic Control of the Pituitary
Copyright © 2009 Pearson Education Inc.
23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The anterior pituitary is a true endocrine gland,
composed of several types of hormone-secreting
cells enmeshed in a network of capillaries.
 The posterior pituitary, however, develops as an
outgrowth of the hypothalamus.
• It consists of a capillary bed and the endings of
neurosecretory cells whose cell bodies are in the
hypothalamus.
 The hypothalamus controls the release of
hormones from both parts of the pituitary.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Hormones from the hypothalamus control
release in the anterior pituitary.
• Neurosecretory cells of the hypothalamus
produce nine different hormones that regulate
the release of hormones from the anterior
pituitary.
• These hormones travel between the two
structures by way of a capillary bed.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The anterior pituitary produces and releases
several hormones.
• Four of these regulate hormone production in other
endocrine glands.
• Follicle-stimulating hormone (FSH) and luteinizing
hormone (LH) stimulate production of sperm and
eggs.
• Thyroid-stimulating hormone (TSH) stimulates the
thyroid to release its hormones.
• Adrenocorticotropic hormone (ACTH) stimulates
the release of hormone from the adrenal cortex.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The anterior pituitary produces and releases
several hormones (continued).
• The remaining hormones do not act on other
endocrine glands.
• Prolactin stimulates development of
mammary glands during pregnancy.
• Growth hormone (GH) regulates body
growth by increasing protein synthesis; too
little results in dwarfism, too much in
gigantism.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The posterior pituitary releases hormones
synthesized in the hypothalamus.
• Hormones of the posterior pituitary:
• Antidiuretic hormone (ADH) helps prevent
dehydration by increasing water uptake by the
kidney before it is lost in urine.
• Oxytocin triggers “milk letdown” in nursing mothers
by causing the contraction of muscles around the
mammary glands to expel milk to the infant during
breast-feeding.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Hormones and
breastfeeding
Neurosecretory
cells of the
hypothalamus
release oxytocin
from endings in the
posterior pituitary
hypothalamus
Oxytocin is
carried in the blood
to the breast
Receptors send
nerve impulses to
the hypothalamus
Suckling stimulates
sensory receptors in
the breast
posterior
pituitary
Oxytocin binds to
receptors on milk gland
muscles, causing milk
to be squeezed out
milk gland
muscle cells
duct
milk-producing
cells
nipple
clusters of
milk glands
Fig. 23-7
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The thyroid and parathyroid glands
influence metabolism and calcium levels.
• Lying at the front of the neck, the thyroid gland
produces two major hormones: thyroxine and
calcitonin.
• The parathyroid gland consists of two pairs of
small disks of endocrine cells, one pair on
each side of the back of the thyroid gland;
these cells release parathyroid hormone.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The thyroid and parathyroid glands
larynx
thyroid gland
esophagus
parathyroid
glands
trachea
Fig. 23-8
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Parathyroid hormone and calcitonin regulate
calcium metabolism.
• The proper concentration of calcium is
essential to nerve and muscle function.
• Parathyroid hormone and calcitonin work
together to maintain nearly constant calcium
levels in the blood and body fluids.
• The skeleton and kidneys are the major body
structures that help regulate blood calcium
concentrations.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Thyroxine influences energy metabolism.
• Thyroxine increases metabolism and breaks down
glucose, providing more energy; it also regulates
body temperature.
• In juvenile animals, thyroxine helps regulate growth
by stimulating both metabolic rate and nervous
system development.
• Undersecretion of thyroxine early in life can cause
cretinism, a condition characterized by mental
retardation and dwarfism.
• Too much thyroxine in vertebrates speeds up
development.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Thyroxine release is controlled by the
hypothalamus.
• The release of thyroxine is under control of the
hypothalamus by negative feedback.
• Thyroid-stimulating hormone (TSH) from the anterior
pituitary stimulates the thyroid to release thyroxine;
high thyroxine concentrations in the blood inhibit TSH
release from the anterior pituitary.
• Iodine in the diet is necessary for thyroxine synthesis;
deficiency leads to an enlarged thyroid, called a
goiter.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Goiter
Fig. 23-9
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The pancreas has both digestive and
endocrine functions.
• The pancreas produces both digestive
secretions and hormones.
• The pancreas produces bicarbonate and a
number of enzymes that are released into the
small intestine, promoting food digestion.
• The endocrine portion of the pancreas
consists of clusters of cells called islet cells.
• Each islet cell produces one of two hormones:
insulin or glucagon.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Insulin and glucagon work in opposition to
regulate carbohydrate and fat metabolism:
insulin reduces blood glucose concentration,
and glucagon increases it.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The pancreas
controls blood
glucose levels.
Blood
glucose is
increased
Glucagon stimulates
cells to burn fat instead of
glucose; the liver converts
glycogen to glucose
Eating
raises blood
glucose
high blood
glucose
High blood
glucose stimulates
insulin release and
inhibits glucagon
release
pancreas
glucagon
Insulin stimulates
glucose uptake by
body cells; the liver
converts glucose to
glycogen
Low blood glucose
stimulates glucagon
release and inhibits
insulin release
Exercise,
fasting also
reduce blood
glucose
low blood
glucose
insulin
liver
muscle
Blood
glucose is
reduced
Fig. 23-10
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 If blood glucose rises after you have eaten:
• Step 1: insulin is released by the pancreas.
• Step 2: insulin causes body cells to take up
glucose.
• Step 3: in body cells, glucose is either
metabolized for energy or is converted to fat
or glycogen.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 If blood glucose level drops by skipping a meal:
• Step 1: insulin secretion is inhibited; glucagon
secretion is stimulated.
• Step 2: glucagon activates an enzyme in the liver that
breaks down glycogen, releasing glucose into the
blood.
• Step 3: glucagon also promotes lipid breakdown,
which releases fatty acids that can be metabolized for
energy.
• Step 4: these effects increase blood glucose levels,
which inhibits glucagon secretion.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Diabetes results from malfunctions of the insulin
control system.
• Defects in insulin synthesis or release by the
pancreas—or in the ability of target cells to respond to
insulin in the blood—result in diabetes mellitus.
• Diabetes mellitus is a condition in which blood
glucose levels are high and fluctuate wildly with sugar
intake.
• Severe diabetes causes fat deposits to accumulate in
blood vessels, increasing blood pressure and heart
disease.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Diabetes results from malfunctions of the
insulin control system (continued).
• Diabetes is a major cause of heart attacks.
• Fat deposits in small blood vessels in the
kidneys and the retina of the eye may cause
kidney failure and blindness, respectively.
• Insulin replacement therapy improves glucose
and lipid metabolism, and it improves the
health of diabetics.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The sex organs produce both gametes and
sex hormones.
• The testes secrete several male sex
hormones, all steroids, of which the most
important is testosterone.
• The ovaries secrete two types of steroid
hormones: estrogen and progesterone.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Sex hormone levels increase during puberty.
• Puberty begins when the hypothalamus starts
to secrete increasing amounts of hormones
that stimulate the anterior pituitary to secrete
more lutenizing hormone (LH) and folliclestimulating hormone (FSH) into the blood.
• LH and FSH stimulate target cells in the testes
or ovaries to produce higher levels of sex
hormones.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Sex hormone levels increase during puberty
(continued).
• In females, estrogen released by the ovaries
stimulates the growth of breasts and the
maturation of the female reproductive system,
including the production of mature egg cells.
• Progesterone prepares the reproductive tract
to receive and nourish the fertilized egg, and
is also secreted by the ovaries during
pregnancy.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Sex hormone levels increase during puberty
(continued).
• In males, testosterone, secreted by the testes,
promotes sperm cell production and
stimulates the development of male secondary
sexual attributes.
• These attributes include the growth of body
and facial hair, the development of a large
larynx, which lowers the voice, and increased
muscle growth.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The adrenal glands secrete hormones that
regulate metabolism and responses to
stress.
• The adrenal glands consist of two very
different parts: the adrenal cortex and the
adrenal medulla.
• The cortex secretes two major types of steroid
hormones called glucocorticoids and
mineralocorticoids.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The adrenal glands
The adrenal medulla secretes
epinephrine and norepinephrine
The adrenal cortex
secretes glucocorticoids,
mineralocorticoids,
and testosterone
kidney
Fig. 23-11
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Glucocorticoids help control glucose
metabolism.
• Their release is stimulated by
adrenocorticotropic hormone (ACTH) from the
anterior pituitary.
• ACTH release is stimulated by hormones
produced by the hypothalamus in response to
stimuli, such as trauma, infection, or exposure
to temperature extremes.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Glucocorticoids help control glucose
metabolism.
• Glucocorticoids raise glucose levels in the
blood.
• Glucocorticoids reduce inflammation.
• Excess glucocorticoids cause Cushing’s
syndrome, which is characterized by weight
gain, fragile skin, weakening of the bones,
excessive hair growth, and increased thirst
and urination.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Cushing’s syndrome in an elderly horse
Fig. 23-12
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Mineralocorticoid hormones regulate the
mineral (salt) content of the blood.
• The most important mineralocorticoid is
aldosterone, which helps control sodium
concentrations.
• Sodium ions are the most abundant positive
ions in the blood and extracellular fluid.
• If blood sodium falls, the adrenal cortex
releases aldosterone, which causes the
kidneys and sweat glands to retain sodium.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The hormones of the adrenal medulla prepare
the body for stress and exercise.
• The adrenal medulla is located in the center of each
adrenal gland.
• It produces two hormones: epinephrine and
norepinephrine (also called adrenaline and
noradrenaline, respectively).
• These hormones prepare the body for emergency
action by increasing heart and respiratory rates,
increasing blood pressure, causing blood glucose to
rise, and directing blood flow away from the digestive
tract and toward the brain and muscles.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Hormones are also produced by the pineal
gland, thymus, kidneys, digestive tract, heart,
and fat cells.
• The pineal gland is located between the two
hemispheres of the brain, just above and behind the
hypothalamus.
• The pineal gland produces the hormone melatonin.
• The pineal gland may suppress the onset of puberty.
• It may also play a role in sleep–wake cycles and can
reduce jet lag during long-distance travel.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The thymus is located in the chest cavity
behind the breastbone.
• The thymus produces the hormone thymosin,
which stimulates the reproduction and
development of the T blood cells, which in turn
play crucial roles in the immune response.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The kidney secretes erythropoietin when the
blood is not transporting enough oxygen.
• Erythropoietin stimulates the bone marrow to
produce more oxygen-carrying red blood cells.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 The heart release the hormone, atrial
natriuretic peptide (ANP), which inhibits the
release of ADH and aldosterone, and
increases the excretion of sodium.
• This hormone is released in response to
increased blood volume; ANP helps lower
blood volume.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Fat cells release the hormone leptin.
• Mice genetically engineered to lack the gene
for leptin became obese, and leptin injections
caused them to lose weight.
• Trials of leptin as a human weight-loss aid
have not been encouraging.
• Many people with high levels of leptin seem to
be relatively insensitive to it.
• Leptin also stimulates the growth of new
capillaries and speeds wound healing.
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23.3 What Are The Structures And
Functions Of The Mammalian Endocrine
System?
 Leptin helps regulate body fat.
Fig. 23-13
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