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Chapter 45
• Hormones and the Endocrine System
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The Body’s Long-Distance Regulators
• Animal hormones
– Chemical signals secreted into blood and
communicate regulatory messages within the
body
• Hormones reach all parts of the body
– But only certain cells, target cells, respond
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• Insect metamorphosis
– regulated by hormones
Figure 45.1
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• The endocrine system and the nervous system
act individually and together in regulating an
animal’s physiology
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• nervous system
– Conveys high-speed electrical signals along
specialized cells called neurons
• endocrine system
– Secretes hormones that coordinate slower but
longer-acting responses to stimuli
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Overlap Between Endocrine and Nervous Regulation
• Function together in maintaining homeostasis,
development, and reproduction
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• Specialized nerve cells known as
neurosecretory cells
– Release neurohormones into the blood
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Control Pathways and Feedback Loops
• 3 types of hormonal control pathways
Pathway
Example
Low blood
glucose
Stimulus
Receptor
protein
Pancreas
secretes
glucagon ( )
Endocrine
cell Blood
Pathway
Stimulus
Target
effectors
Suckling
Stimulus
Sensory
neuron
Hypothalamus/
posterior pituitary
Hypothalamus
Neurosecretory
cell
Posterior pituitary
secretes oxytocin
Blood
( )
vessel
Hypothalamic
neurohormone
released in
response to
neural and
hormonal
signals
Neurosecretory
cell
Hypothalamus
secretes prolactinBlood
releasing
vessel
hormone ( )
Liver
Response
(a)
Pathway
Sensory
neuron
vessel
Example
Example
Glycogen
breakdown,
glucose release
into blood
Simple endocrine pathway
Target
effectors
Anterior
pituitary
secretes
Endocrine prolactin ( )
Smooth muscle
in breast
cell
Response
(b) Simple
Blood
vessel
Milk release
neurohormone pathway
Target
effectors
Response
Figure 45.2a–c
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(c)
Mammary glands
Milk production
Simple neuroendocrine pathway
• Common feature of control pathways
feedback loop connecting the response to the
initial stimulus
e.g. Negative feedback
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• Hormones bind to target cell receptors 
pathways  cell responses
• Hormones  bloodstream  target cells
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• 3 classes of hormones
– Proteins and peptides
– Amines derived from amino acids
– Steroids
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•
Signaling involves:
1. Reception
2. Signal transduction
3. Response
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Cell-Surface Receptors for Water-Soluble Hormones
• Embedded in membrane, project from cell
surface
SECRETORY
CELL
Hormone
molecule
VIA
BLOOD
Signal receptor
Signal
transduction
pathway
TARGET
CELL
OR
Cytoplasmic
response
DNA
Nuclear
response
Figure 45.3a
(a) Receptor in plasma membrane
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NUCLEUS
• Binding of a hormone  transduction pathway
 specific responses
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• The same hormone may have different effects
on target cells that have
– Different receptors
– Different signal transduction pathways
– Different proteins for carrying out the response
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• e.g. epinephrine has multiple effects
Different receptors
different cell responses
Epinephrine
Epinephrine
Epinephrine
a receptor
b receptor
b receptor
Glycogen
deposits
Vessel
dilates
Vessel
constricts
(a) Intestinal blood
vessel
Figure 45.4a–c
(b) Skeletal muscle
blood vessel
Different intracellular proteins
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Glycogen
breaks down
and glucose
is released
from cell
(c) Liver cell
different cell responses
Intracellular Receptors for Lipid-Soluble Hormones
• Steroids Enter target cells, bind to protein
receptors in the cytoplasm or nucleus
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• Results in regulation of specific genes
SECRETORY
CELL
Hormone
molecule
VIA
BLOOD
TARGET
CELL
Signal
receptor
DNA
Signal
transduction
and response
mRNA
NUCLEUS
Synthesis of
specific proteins
Figure 45.3b
(b) Receptor in cell nucleus
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Paracrine Signaling
• Signals elicit responses in nearby target cells
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• e.g. Prostaglandins help regulate the
aggregation of platelets in blood clots
Figure 45.5
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• The hypothalamus and the pituitary gland
– Control much of the endocrine system
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• The major human endocrine glands
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Adrenal glands
Pancreas
Ovary
(female)
Testis
(male)
Figure 45.6
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Table 45.1
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Table 45.1
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Hypothalamus and Pituitary Gland
• Direct-acting hormones are stored in and released
from the posterior pituitary
Hypothalamus
Neurosecretory
cells of the
Axon
hypothalamus
Posterior
pituitary
HORMONE
Figure 45.7
TARGET
Anterior
pituitary
ADH
Oxytocin
Kidney tubules
Mammary glands,
uterine muscles
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• Other hormones are secreted into the blood and
transported to the anterior pituitary
Neurosecretory cells
of the hypothalamus
Tropic Effects Only
FSH, follicle-stimulating hormone
LH, luteinizing hormone
TSH, thyroid-stimulating hormone
ACTH, adrenocorticotropic hormone
Nontropic Effects Only
Prolactin
MSH, melanocyte-stimulating hormone
Endorphin
Portal vessels
Nontropic and Tropic Effects
Growth hormone
Endocrine cells of the
Hypothalamic
releasing
hormones
(red dots)
HORMONE
TARGET
FSH and LH
Testes or
ovaries
anterior pituitary
Pituitary hormones
(blue dots)
TSH
ACTH
Prolactin
MSH
Thyroid
Adrenal
cortex
Mammary
glands
Melanocytes
Figure 45.8
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Endorphin Growth hormone
Pain receptors
in the brain
Liver
Bones
• Antidiuretic hormone (ADH)
– water reabsorption in the kidneys
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• Growth hormone (GH)
– Promotes growth and has diverse metabolic
effects
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Thyroid Hormones
• Produces 2 iodine-containing hormones,
T3 & T4
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• The hypothalamus and anterior pituitary
– Control the thyroid through negative feedback
Hypothalamus
Anterior
pituitary
TSH
Thyroid
Figure 45.9
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T3
+
T4
• Thyroid hormones
– Stimulate metabolism and influence
development and maturation
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• Hyperthyroidism, excessive secretion of thyroid
hormones
 Graves’ disease in humans
Figure 45.10
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Parathyroid Hormone and Calcitonin: Control of
Blood Calcium
• 2 antagonistic hormones, parathyroid hormone
Calcitonin
(PTH) and calcitonin
Thyroid gland
releases
calcitonin.
Reduces
Ca2+ uptake
in kidneys
Stimulates
Ca2+ deposition
in bones
Blood Ca2+
level declines
to set point
Rising blood
Ca2+
level
Homeostasis:
Blood Ca2+ level
(about 10 mg/100 mL)
Falling blood
Blood Ca2+
level rises
to set point
Ca2+ level
Stimulates
Ca2+ release
Parathyroid
gland
from bones
PTH
Increases
Ca2+ uptake
in intestines
Figure 45.11
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Active
vitamin D
Stimulates Ca2+
uptake in kidneys
Insulin and Glucagon: Control of Blood Glucose
• 2 types of cells in the pancreas secrete insulin
and glucagon, antagonistic hormones that
maintain glucose homeostasis and are found in
the islets of Langerhans
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• Glucagon
– produced by alpha cells
• Insulin
– produced by beta cells
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• Maintenance of glucose homeostasis
Body cells
take up more
glucose.
Insulin
Beta cells of
pancreas are stimulated
to release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Blood glucose level
declines to set point;
stimulus for insulin
release diminishes.
Rising blood glucose
level (for instance, after
eating a carbohydraterich meal)
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes.
STIMULUS:
Dropping blood glucose
level (for instance, after
skipping a meal)
Alpha cells of pancreas
Figure 45.12
Liver breaks
down glycogen
and releases
glucose into
blood.
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are stimulated to release
glucagon into the blood.
Glucagon
• Insulin reduces blood glucose levels by
– Cellular uptake of glucose
– Slowing glycogen breakdown in the liver
– Fat storage
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• Glucagon increases blood glucose levels by
– Conversion of glycogen to glucose in the liver
– Breakdown of fat and protein into glucose
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Diabetes Mellitus
• Perhaps the best-known endocrine disorder
– Deficiency of insulin or a decreased response
to insulin in target tissues
Elevated blood glucose levels
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• Type I diabetes (insulin-dependent)
– autoimmune disorder, immune system destroys
the beta cells of the pancreas
• Type II diabetes (non-insulin-dependent)
– deficiency of insulin or, reduced responsiveness of
target cells due to some change in insulin
receptors
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Adrenal Hormones: Response to Stress
• adjacent to kidneys
• adrenal medulla & adrenal cortex
• secretes epinephrine and norepinephrine
• Mediate various fight-or-flight responses
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• Mediate various fight-or-flight responses
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• Glucocorticoids, e.g. cortisol
– glucose metabolism
• Mineralocorticoids, e.g. aldosterone
– salt and water balance
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• Stress and the adrenal gland
Stress
Spinal cord
(cross section)
Nerve
signals
Hypothalamus
Releasing
hormone
Nerve
cell
Anterior pituitary
Blood vessel
Adrenal medulla
Nerve cell
secretes epinephrine
and norepinephrine.
Adrenal cortex
secretes
mineralocorticoids
and glucocorticoids.
ACTH
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
Figure 45.13a,b
5. Change in blood flow patterns, leading to
increased alertness and decreased digestive
and kidney activity
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(b) Long-term stress response
Effects of
mineralocorticoids:
1. Retention of sodium
ions and water by
kidneys
2. Increased blood
volume and blood
pressure
Effects of
glucocorticoids:
1. Proteins and fats
broken down and
converted to glucose,
leading to increased
blood glucose
2. Immune
system may
be suppressed
Gonadal Sex Hormones
• The gonads (testes and ovaries)
– Produce androgens, estrogens, and progestins
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• Testes synthesize androgens (e.g.
testosterone)
– Development and maintenance of the male
reproductive system, increase in muscle mass
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• Estrogen
– maintenance of female reproductive system
and the development of female secondary sex
characteristics
• Progesterone
– preparing and maintaining the uterus
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Melatonin and Biorhythms
• Pineal gland (located within brain)
– Secretes melatonin
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• Release of melatonin
– Controlled by light/dark cycles
• Function of melatonin
biological rhythms associated with reproduction
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• e.g. insects
– Molting and development controlled by
hormones
Brain
1 Neurosecretory cells in the brain produce
brain hormone (BH), which is stored in
the corpora cardiaca (singular, corpus
cardiacum) until release.
Neurosecretory cells
Brain
hormone (BH)
Corpus cardiacum
Corpus allatum
Low
JH
Prothoracic
gland
Ecdysone
Juvenile
hormone
(JH)
2 BH signals its main target
organ, the prothoracic
gland, to produce the
hormone ecdysone.
3
Figure 45.15
Ecdysone secretion
from the prothoracic
gland is episodic, with
each release stimulating
a molt.
EARLY
LARVA
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LATER
LARVA
PUPA
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. 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.
ADULT
• Brain hormone
release of ecdysone from the prothoracic
glands
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• Ecdysone
molting & development of adult characteristics
• Juvenile hormone
retention of larval characteristics
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