Download Hormone

Chapter 45 – Edited by Hawes
Hormones and the
Endocrine System
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: The Body’s Long-Distance Regulators
• Animal hormones are chemical signals that
are secreted into the circulatory system and
communicate regulatory messages within the
body
• Hormones reach all parts of the body, but only
target cells are equipped to respond
• Insect metamorphosis is regulated by
hormones
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• Two systems coordinate communication
throughout the body: the endocrine system and
the nervous system
• The endocrine system secretes hormones
that coordinate slower but longer-acting
responses including reproduction,
development, energy metabolism, growth, and
behavior
• The nervous system conveys high-speed
electrical signals along specialized cells called
neurons; these signals regulate other cells
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Concept 45.1: Hormones and other signaling
molecules bind to target receptors, triggering
specific response pathways
• Chemical signals bind to receptor proteins on
target cells
• Only target cells respond to the signal
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Types of Secreted Signaling Molecules
• Secreted chemical signals include
– Hormones
– Local regulators
– Neurotransmitters
– Neurohormones
– Pheromones
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Hormones
• Endocrine signals (hormones) are secreted into
extracellular fluids and travel via the
bloodstream
• Endocrine glands are ductless and secrete
hormones directly into surrounding fluid
• Hormones mediate responses to environmental
stimuli and regulate growth, development, and
reproduction
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Fig. 45-2
Intercellular
communication by
secreted
molecules. In each
type of signaling,
secreted molecules
bind to a specific
receptor protein
expressed by
target cells.
Receptors are
sometimes located
inside cells, but for
simplicity all are
drawn here on the
cell surface.
Blood
vessel
(a) Endocrine signaling
(b) Paracrine signaling
(c) Autocrine signaling
Neuron
(d) Synaptic signaling
Neurosecretory
cell
Blood
vessel
(e) Neuroendocrine signaling
a) In endocrine signaling,
secreted molecules diffuse
into the blood stream and
Response
trigger responses in target
cells anywhere in the body.
b) In paracrine signaling,
secreted molecules diffuse
locally and trigger a
Response
response in neighboring
cells.
c) In
autocrine signaling, secreted
molecules diffuse locally and
trigger a response in the
Response
cells that secrete them.
Synapse d) In synaptic signaling,
neurotransmitters diffuse
across synapses and trigger
responses in cells of target
Response
tissues (neurons, muscles,
or glands).
e) In
neuroendocrine signaling,
neurohormones diffuse into
the bloodstream and trigger
Response
responses in target cells
anywhere in the body.
• Exocrine glands have ducts and secrete
substances onto body surfaces or into body
cavities (for example, tear ducts)
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Local Regulators
• Local regulators are chemical signals that
travel over short distances by diffusion
• Local regulators help regulate blood pressure,
nervous system function, and reproduction
• Local regulators are divided into two types
– Paracrine signals act on cells near the
secreting cell
– Autocrine signals act on the secreting cell
itself
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Fig. 45-2a
Blood
vessel
Response
(a) Endocrine signaling
Response
(b) Paracrine signaling
Response
(c) Autocrine signaling
Neurotransmitters and Neurohormones
• Neurons (nerve cells) contact target cells at
synapses
• At synapses, neurons often secrete chemical
signals called neurotransmitters that diffuse a
short distance to bind to receptors on the target
cell
• Neurotransmitters play a role in sensation,
memory, cognition, and movement
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Fig. 45-2b
Synapse
Neuron
Response
(d) Synaptic signaling
Neurosecretory
cell
Blood
vessel
(e) Neuroendocrine signaling
Response
• Neurohormones are a class of hormones that
originate from neurons in the brain and diffuse
through the bloodstream
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Pheromones
• Pheromones are chemical signals that are
released from the body and used to
communicate with other individuals in the
species
• Pheromones mark trails to food sources, warn
of predators, and attract potential mates
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Chemical Classes of Hormones
• Three major classes of molecules function as
hormones in vertebrates:
– Polypeptides (proteins and peptides)
– Amines derived from amino acids
– Steroid hormones
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• Lipid-soluble hormones (steroid hormones)
pass easily through cell membranes, while
water-soluble hormones (polypeptides and
amines) do not
• The solubility of a hormone correlates with the
location of receptors inside or on the surface of
target cells
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Fig. 45-3
Hormones differ
in form and
solubility.
Structures of
insulin, a
polypeptide
hormone;
epinephrine and
thyroxine, amine
hormones; and
cortisol, a steroid
hormone. Insulin
and epinephrine
are water soluble;
thyroxine and
cortisol are lipid
soluble.
Water-soluble
Lipid-soluble
0.8 nm
Polypeptide:
Insulin
Steroid:
Cortisol
Amine:
Epinephrine
Amine:
Thyroxine
Hormone Receptor Location: Scientific Inquiry
• In the 1960s, researchers studied the
accumulation of radioactive steroid hormones in
rat tissue
• These hormones accumulated only in target cells
that were responsive to the hormones
• These experiments led to the hypothesis that
receptors for the steroid hormones are located
inside the target cells
• Further studies have confirmed that receptors for
lipid-soluble hormones such as steroids are
located inside cells
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• Researchers hypothesized that receptors for
water-soluble hormones would be located on
the cell surface
• They injected a water-soluble hormone into the
tissues of frogs
• The hormone triggered a response only when it
was allowed to bind to cell surface receptors
• This confirmed that water-soluble receptors
were on the cell surface
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Cellular Response Pathways
• Water and lipid soluble hormones differ in their
paths through a body
• Water-soluble hormones are secreted by
exocytosis, travel freely in the bloodstream,
and bind to cell-surface receptors
• Lipid-soluble hormones diffuse across cell
membranes, travel in the bloodstream bound to
transport proteins, and diffuse through the
membrane of target cells
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• Signaling by any of these hormones involves
three key events:
– Reception
– Signal transduction
– Response
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Fig. 45-5-1
Receptor
location varies
with hormone
type.
a) A water
soluble
hormone binds
to a signal
receptor protein
on the surface
of a target cell.
This interaction
triggers events
that lead to
either a change
in cytoplasmic
function or a
change in gene
transcription in
the nucleus.
Fat-soluble
hormone
Watersoluble
hormone
Signal receptor
Transport
protein
TARGET
CELL
(a)
Signal
receptor
NUCLEUS
(b)
b) A lipid
soluble
hormone
penetrates the
target cell’s
plasma
membrane and
binds to an
intracellular
signal receptor,
either in the
cytoplasm or in
the nucleus.
The hormone
receptor
complex acts
as a
transcription
factor, typically
activating gene
expression.
Fig. 45-5-2
Fat-soluble
hormone
Watersoluble
hormone
Transport
protein
Signal receptor
TARGET
CELL
Cytoplasmic
response
OR
Signal
receptor
Gene
regulation
Cytoplasmic
response
(a)
NUCLEUS
(b)
Gene
regulation
Pathway for Water-Soluble Hormones
• Binding of a hormone to its receptor initiates a
signal transduction pathway leading to
responses in the cytoplasm, enzyme activation,
or a change in gene expression
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• The hormone epinephrine has multiple effects
in mediating the body’s response to short-term
stress
• Epinephrine binds to receptors on the plasma
membrane of liver cells
• This triggers the release of messenger
molecules that activate enzymes and result in
the release of glucose into the bloodstream
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Fig. 45-6-1
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Second
messenger
Cell-surface hormone receptors trigger signal
transduction.
Fig. 45-6-2
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Inhibition of
glycogen synthesis
Promotion of
glycogen breakdown
Protein
kinase A
Second
messenger
Pathway for Lipid-Soluble Hormones
• The response to a lipid-soluble hormone is
usually a change in gene expression
• Steroids, thyroid hormones, and the hormonal
form of vitamin D enter target cells and bind to
protein receptors in the cytoplasm or nucleus
• Protein-receptor complexes then act as
transcription factors in the nucleus, regulating
transcription of specific genes
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Fig. 45-7-1
Hormone
(estradiol)
Estradiol
(estrogen)
receptor
Plasma
membrane
Hormone-receptor
complex
Steroid hormone receptors directly regulate gene
expression.
Fig. 45-7-2
Hormone
(estradiol)
Estradiol
(estrogen)
receptor
Plasma
membrane
Hormone-receptor
complex
DNA
Vitellogenin
mRNA
for vitellogenin
Multiple Effects of Hormones
• The same hormone may have different effects
on target cells that have
– Different receptors for the hormone
– Different signal transduction pathways
– Different proteins for carrying out the response
• A hormone can also have different effects in
different species
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Fig. 45-8-1
Same receptors but different
intracellular proteins (not shown)
Epinephrine
Epinephrine
 receptor
 receptor
Glycogen
deposits
Glycogen
breaks down
and glucose
is released.
(a) Liver cell
Vessel
dilates.
(b) Skeletal muscle
blood vessel
One hormone, different
effects. Epinephrine, the
primary “fight-or-flight”
hormone, produces
different responses in
different target cells.
Target cells with the
same receptor exhibit
different responses if
they have different
signal transduction
pathways and/or
effector proteins.
Responses of target
cells may also differ if
they have different
receptors for the
hormone.
Fig. 45-8-2
Same receptors but different
intracellular proteins (not shown)
Different receptors
Epinephrine
Epinephrine
Epinephrine
 receptor
 receptor
 receptor
Glycogen
deposits
Glycogen
breaks down
and glucose
is released.
(a) Liver cell
Vessel
dilates.
(b) Skeletal muscle
blood vessel
Vessel
constricts.
(c) Intestinal blood
vessel
Fig. 45-9
Specialized role of a hormone in frog metamorphosis. The
hormone thyroxine is responsible for the resorption of the
tadpole’s tail as the frog
(a)
develops into its adult form.
(b)
Signaling by Local Regulators
• In paracrine signaling, nonhormonal chemical
signals called local regulators elicit responses
in nearby target cells
• Types of local regulators:
– Cytokines and growth factors
– Nitric oxide (NO)
– Prostaglandins
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• Prostaglandins help regulate aggregation of
platelets, an early step in formation of blood
clots
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Concept 45.2: Negative feedback and antagonistic
hormone pairs are common features of the
endocrine system
• Hormones are assembled into regulatory
pathways
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Fig. 45-10
Major endocrine glands:
Hypothalamus
Major human
endocrine glands.
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Organs containing
endocrine cells:
Thymus
Heart
Adrenal
glands
Testes
Liver
Stomach
Pancreas
Kidney
Kidney
Small
intestine
Ovaries
Simple Hormone Pathways
• Hormones are released from an endocrine cell,
travel through the bloodstream, and interact
with the receptor or a target cell to cause a
physiological response
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Fig. 45-11
A simple
endocrine
pathway. A
change in
some internal
or external
variable – the
stimulus –
causes the
endocrine cell
to secrete a
hormone (red
dots). Upon
reaching its
target cell via
the
bloodstream,
the hormone
binds to its
receptor,
triggering
signal
transduction
that results in
a specific
response.
Pathway
–
Example
Stimulus
Low pH in
duodenum
S cells of duodenum
secrete secretin ( )
Endocrine
cell
Secretin
signaling is an
example of a
simple
endocrine
pathway.
Blood
vessel
Target
cells
Response
Pancreas
Bicarbonate release
• A negative feedback loop inhibits a response
by reducing the initial stimulus
• Negative feedback regulates many hormonal
pathways involved in homeostasis
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Insulin and Glucagon: Control of Blood Glucose
• Insulin and glucagon are antagonistic
hormones that help maintain glucose
homeostasis
• The pancreas has clusters of endocrine cells
called islets of Langerhans with alpha cells
that produce glucagon and beta cells that
produce insulin
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Fig. 45-12-5
Maintenance
of glucose
homeostasis
by insulin
and
glucagon.
The
antagonistic
effects of
insulin and
glucagon
help
maintain the
blood
glucose level
near its set
point.
Body cells
take up more
glucose.
Insulin
Beta cells of
pancreas
release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Blood glucose level
rises.
Blood glucose
level declines.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
STIMULUS:
Blood glucose level
falls.
Blood glucose
level rises.
Alpha cells of pancreas
release glucagon.
Liver breaks
down glycogen
and releases
glucose.
Glucagon
Target Tissues for Insulin and Glucagon
• Insulin reduces blood glucose levels by
– Promoting the cellular uptake of glucose
– Slowing glycogen breakdown in the liver
– Promoting fat storage
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• Glucagon increases blood glucose levels by
– Stimulating conversion of glycogen to glucose
in the liver
– Stimulating breakdown of fat and protein into
glucose
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Diabetes Mellitus
• Diabetes mellitus is perhaps the best-known
endocrine disorder
• It is caused by a deficiency of insulin or a
decreased response to insulin in target tissues
• It is marked by elevated blood glucose levels
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• Type I diabetes mellitus (insulin-dependent) is
an autoimmune disorder in which the immune
system destroys pancreatic beta cells
• Type II diabetes mellitus (non-insulindependent) involves insulin deficiency or
reduced response of target cells due to change
in insulin receptors
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Concept 45.3: The endocrine and nervous systems act
individually and together in regulating animal
physiology
• Signals from the nervous system initiate and
regulate endocrine signals
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Coordination of Endocrine and Nervous Systems
in Invertebrates
• In insects, molting and development are
controlled by a combination of hormones:
– A brain hormone stimulates release of
ecdysone from the prothoracic glands
– Juvenile hormone promotes retention of larval
characteristics
– Ecdysone promotes molting (in the presence of
juvenile hormone) and development (in the
absence of juvenile hormone) of adult
characteristics
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Fig. 45-13-1
Brain
Neurosecretory cells
Corpus cardiacum
PTTH
Corpus allatum
Hormonal regulation of insect
development. Most insects go through a
Prothoracic
gland
Ecdysone
EARLY
LARVA
series of larval stages, with each molt
(shedding of the old exoskeleton) leading to a
Juvenile larger larva. Molting of the final larval stage
hormone gives rise to a pupa, in which metamorphosis
(JH)
produces the adult form of the insect.
Hormones control the progression of stages.
1. Neurosecretory cells in the brain produce
prothoracicotropic hormone (PTTH), which is
stored in the corpora cardiaca until release.
2. PTTH signals its main target organ, the
prothoracic gland, to produce the hormone
ecdysone.
3. Ecdysone secretion from the prothoracic
gland is episodic, with each release stimulating
a molt.
Fig. 45-13-2
Brain
Neurosecretory cells
Corpus cardiacum
PTTH
Corpus allatum
Prothoracic
gland
Ecdysone
EARLY
LARVA
Juvenile
hormone
(JH)
LATER
LARVA
4. Juvenile hormone (JH),
secreted by the corpora allata,
determines the result of the molt.
At relatively high concentrations
of JH, ecdysone-stimulated
molting produces another larval
stage because JH suppresses
metamorphosis. But when levels
of JH fall below a certain
concentration, a pupa forms at
the next ecdysone-induced molt.
The adult insect emerges from
the pupa.
Fig. 45-13-3
Brain
Neurosecretory cells
Corpus cardiacum
PTTH
Corpus allatum
Low
JH
Prothoracic
gland
Ecdysone
EARLY
LARVA
Juvenile
hormone
(JH)
LATER
LARVA
PUPA
ADULT
Coordination of Endocrine and Nervous Systems
in Vertebrates
• The hypothalamus receives information from
the nervous system and initiates responses
through the endocrine system
• Attached to the hypothalamus is the pituitary
gland composed of the posterior pituitary and
anterior pituitary
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• The posterior pituitary stores and secretes
hormones that are made in the hypothalamus
• The anterior pituitary makes and releases
hormones under regulation of the
hypothalamus
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Fig. 45-14
Cerebrum
Pineal
gland
Thalamus
Cerebellum
Pituitary
gland
Spinal cord
Endocrine glands in the
human brain. This side view
of the brain indicates the
Posterior
position of the
pituitary
hypothalamus, the pituitary
gland, and the pineal gland,
which plays a role in
regulating biorhythm.
Hypothalamus
Hypothalamus
Anterior
pituitary
Table 45-1
Table 45-1a
Posterior Pituitary Hormones
• The two hormones released from the posterior
pituitary act directly on nonendocrine tissues
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Fig. 45-15
Production and release of posterior pituitary
hormones. The posterior pituitary gland is
an extension of the hypothalamus. Certain
neurosecretory cells in the hypothalamus
make antidiuretic hormone (ADH) and
oxytocin, which are transported to the
posterior pituitary, where they are stored.
Nerve signals from the
Neurosecretory
brain trigger release of
cells of the
these neurohormones
hypothalamus
(red dots).
Hypothalamus
Axon
Posterior
pituitary
Anterior
pituitary
HORMONE
ADH
Oxytocin
TARGET
Kidney tubules
Mammary glands,
uterine muscles
• Oxytocin induces uterine contractions and the
release of milk
• Suckling sends a message to the
hypothalamus via the nervous system to
release oxytocin, which further stimulates the
milk glands
• This is an example of positive feedback,
where the stimulus leads to an even greater
response
• Antidiuretic hormone (ADH) enhances water
reabsorption in the kidneys
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Fig. 45-16
Pathway
Example
Stimulus
Suckling
+
Sensory
neuron
Hypothalamus/
posterior pituitary
Positive feedback
A simple
neurohormone
pathway. In this
example, the
stimulus causes
the hypothalamus
to send a nerve
impulse to the
posterior pituitary,
which responds
by secreting a
neurohormone
(red squares).
Upon reaching its
target cell via the
bloodstream, the
neurohormone
binds to its
receptor,
triggering signal
transduction that
results in a
specific
response.
Neurosecretory
cell
Blood
vessel
Target
cells
Response
In the neurohormone
pathway for oxytocin
signaling, the
response increases
the stimulus, forming
a positive-feedback
loop that amplifies
signaling in the
pathway.
Posterior pituitary
secretes oxytocin ( )
Smooth muscle in
breasts
Milk release
Anterior Pituitary Hormones
• Hormone production in the anterior pituitary is
controlled by releasing and inhibiting hormones
from the hypothalamus
• For example, the production of thyrotropin
releasing hormone (TRH) in the hypothalamus
stimulates secretion of the thyroid stimulating
hormone (TSH) from the anterior pituitary
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Fig. 45-17
Tropic effects only:
FSH
LH
TSH
ACTH
Neurosecretory cells
of the hypothalamus
Nontropic effects only:
Prolactin
MSH
Nontropic and tropic effects:
GH
Hypothalamic
releasing and
inhibiting
hormones
Portal vessels
Endocrine cells of
the anterior pituitary
Posterior pituitary
Pituitary hormones
HORMONE
FSH and LH
TSH
ACTH
Prolactin
MSH
GH
TARGET
Testes or
ovaries
Thyroid
Adrenal
cortex
Mammary
glands
Melanocytes
Liver, bones,
other tissues
Production and release of anterior pituitary hormones.
Hormone Cascade Pathways
• A hormone can stimulate the release of a
series of other hormones, the last of which
activates a nonendocrine target cell; this is
called a hormone cascade pathway
• The release of thyroid hormone results from a
hormone cascade pathway involving the
hypothalamus, anterior pituitary, and thyroid
gland
• Hormone cascade pathways are usually
regulated by negative feedback
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Fig. 45-18-1
Example
Pathway
Cold
Stimulus
Sensory
neuron
Hypothalamus secretes
thyrotropin-releasing
hormone (TRH )
Neurosecretory
cell
Blood
vessel
A hormone cascade
pathway.
Fig. 45-18-2
Example
Pathway
+
Stimulus
Cold
Sensory
neuron
Hypothalamus secretes
thyrotropin-releasing
hormone (TRH )
Neurosecretory
cell
Blood
vessel
Anterior pituitary secretes
thyroid-stimulating
hormone (TSH
or thyrotropin )
Fig. 45-18-3
Pathway
Example
Stimulus
Cold
Sensory
neuron
–
Hypothalamus secretes
thyrotropin-releasing
hormone (TRH )
Neurosecretory
cell
Blood
vessel
–
Negative feedback
Anterior pituitary secretes
thyroid-stimulating
hormone (TSH
or thyrotropin )
Thyroid gland secretes
thyroid hormone
(T3 and T4 )
Target
cells
Response
Body tissues
Increased cellular
metabolism
Tropic Hormones
• A tropic hormone regulates the function of
endocrine cells or glands
• The four strictly tropic hormones are
– Thyroid-stimulating hormone (TSH)
– Follicle-stimulating hormone (FSH)
– Luteinizing hormone (LH)
– Adrenocorticotropic hormone (ACTH)
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Nontropic Hormones
• Nontropic hormones target nonendocrine
tissues
• Nontropic hormones produced by the anterior
pituitary are
– Prolactin (PRL)
– Melanocyte-stimulating hormone (MSH)
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• Prolactin stimulates lactation in mammals but
has diverse effects in different vertebrates
• MSH influences skin pigmentation in some
vertebrates and fat metabolism in mammals
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Growth Hormone
• Growth hormone (GH) is secreted by the
anterior pituitary gland and has tropic and
nontropic actions
• It promotes growth directly and has diverse
metabolic effects
• It stimulates production of growth factors
• An excess of GH can cause gigantism, while a
lack of GH can cause dwarfism
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Concept 45.4: Endocrine glands respond to diverse
stimuli in regulating metabolism, homeostasis,
development, and behavior
• Endocrine signaling regulates metabolism,
homeostasis, development, and behavior
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Thyroid Hormone: Control of Metabolism and
Development
• The thyroid gland consists of two lobes on the
ventral surface of the trachea
• It produces two iodine-containing hormones:
triiodothyronine (T3) and thyroxine (T4)
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• Thyroid hormones stimulate metabolism and
influence development and maturation
• Hyperthyroidism, excessive secretion of thyroid
hormones, causes high body temperature,
weight loss, irritability, and high blood pressure
• Graves’ disease is a form of hyperthyroidism in
humans
• Hypothyroidism, low secretion of thyroid
hormones, causes weight gain, lethargy, and
intolerance to cold
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Fig. 45-19
Thyroid scan. A tumor in one lobe of the
thyroid gland caused the accumulation of
radioactive iodine.
High level
iodine
uptake
Normal
iodine
uptake
• Proper thyroid function requires dietary iodine
for hormone production
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Parathyroid Hormone and Vitamin D: Control of
Blood Calcium
• Two antagonistic hormones regulate the
homeostasis of calcium (Ca2+) in the blood of
mammals
– Parathyroid hormone (PTH) is released by
the parathyroid glands
– Calcitonin is released by the thyroid gland
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Fig. 45-20-1
The roles of parathyroid hormone (PTH) in regulating
blood calcium levels in mammals.
PTH
Parathyroid gland
(behind thyroid)
STIMULUS:
Falling blood
Ca2+ level
Homeostasis:
Blood Ca2+ level
(about 10 mg/100 mL)
Fig. 45-20-2
Active
vitamin D
Increases
Ca2+ uptake
in intestines
Stimulates Ca2+
uptake in kidneys
PTH
Stimulates
Ca2+ release
from bones
Parathyroid gland
(behind thyroid)
STIMULUS:
Falling blood
Ca2+ level
Blood Ca2+
level rises.
Homeostasis:
Blood Ca2+ level
(about 10 mg/100 mL)
• PTH increases the level of blood Ca2+
– It releases Ca2+ from bone and stimulates
reabsorption of Ca2+ in the kidneys
– It also has an indirect effect, stimulating the
kidneys to activate vitamin D, which promotes
intestinal uptake of Ca2+ from food
• Calcitonin decreases the level of blood Ca2+
– It stimulates Ca2+ deposition in bones and
secretion by kidneys
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Adrenal Hormones: Response to Stress
• The adrenal glands are adjacent to the kidneys
• Each adrenal gland actually consists of two
glands: the adrenal medulla (inner portion) and
adrenal cortex (outer portion)
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Catecholamines from the Adrenal Medulla
• The adrenal medulla secretes epinephrine
(adrenaline) and norepinephrine
(noradrenaline)
• These hormones are members of a class of
compounds called catecholamines
• They are secreted in response to stressactivated impulses from the nervous system
• They mediate various fight-or-flight responses
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• Epinephrine and norepinephrine
– Trigger the release of glucose and fatty acids
into the blood
– Increase oxygen delivery to body cells
– Direct blood toward heart, brain, and skeletal
muscles, and away from skin, digestive
system, and kidneys
• The release of epinephrine and norepinephrine
occurs in response to nerve signals from the
hypothalamus
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Fig. 45-21
Stress
and the adrenal gland. Stressful
stimuli cause the hypothalmus to activate. a)
the adrenal medulla via nerve impulses
Spinal cord
Nerve
signals
Releasing
hormone
Nerve
cell
ACTH
b) The adrenal cortex via
hormonal signals. The adrenal
medulla mediates short-term
Stress
responses to stress by
secreting the catecholamine
Hypothalamus hormones epinephrine and
norepinephrine. The adrenal
cortex controls more
prolonged
Anterior pituitary
Blood vessel responses by secreting
corticosteroids.
Adrenal medulla
Adrenal cortex
Adrenal
gland
Kidney
(a) Short-term stress response
Effects of epinephrine and norepinephrine:
1. Glycogen broken down to glucose; increased blood glucose
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
5. Change in blood flow patterns, leading to increased
alertness and decreased digestive, excretory, and
reproductive system activity
(b) Long-term stress response
Effects of
mineralocorticoids:
Effects of
glucocorticoids:
1. Retention of sodium 1. Proteins and fats broken down
ions and water by
and converted to glucose, leading
kidneys
to increased blood glucose
2. Increased blood
volume and blood
pressure
2. Possible suppression of
immune system
Fig. 45-21b
Adrenal medulla
Adrenal
gland
Kidney
(a) Short-term stress response
Effects of epinephrine and norepinephrine:
1. Glycogen broken down to glucose; increased blood glucose
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
5. Change in blood flow patterns, leading to increased
alertness and decreased digestive, excretory, and
reproductive system activity
Steroid Hormones from the Adrenal Cortex
• The adrenal cortex releases a family of steroids
called corticosteroids in response to stress
• These hormones are triggered by a hormone
cascade pathway via the hypothalamus and
anterior pituitary
• Humans produce two types of corticosteroids:
glucocorticoids and mineralocorticoids
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Fig. 45-21c
Adrenal cortex
Adrenal
gland
Kidney
(b) Long-term stress response
Effects of
mineralocorticoids:
Effects of
glucocorticoids:
1. Retention of sodium
ions and water by
kidneys
1. Proteins and fats broken down
and converted to glucose, leading
to increased blood glucose
2. Increased blood
volume and blood
pressure
2. Possible suppression of
immune system
• Glucocorticoids, such as cortisol, influence
glucose metabolism and the immune system
• Mineralocorticoids, such as aldosterone,
affect salt and water balance
• The adrenal cortex also produces small
amounts of steroid hormones that function as
sex hormones
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Gonadal Sex Hormones
• The gonads, testes and ovaries, produce most
of the sex hormones: androgens, estrogens,
and progestins
• All three sex hormones are found in both males
and females, but in different amounts
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• The testes primarily synthesize androgens,
mainly testosterone, which stimulate
development and maintenance of the male
reproductive system
• Testosterone causes an increase in muscle
and bone mass and is often taken as a
supplement to cause muscle growth, which
carries health risks
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• Estrogens, most importantly estradiol, are
responsible for maintenance of the female
reproductive system and the development of
female secondary sex characteristics
• In mammals, progestins, which include
progesterone, are primarily involved in
preparing and maintaining the uterus
• Synthesis of the sex hormones is controlled by
FSH and LH from the anterior pituitary
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Melatonin and Biorhythms
• The pineal gland, located in the brain,
secretes melatonin
• Light/dark cycles control release of melatonin
• Primary functions of melatonin appear to relate
to biological rhythms associated with
reproduction
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