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Biology
A Guide to the Natural World
Chapter 28 • Lecture Outline
Communication and Control 2: The Endocrine System
Fifth Edition
David Krogh
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28.1 The Endocrine System in
Overview
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The Endocrine System
• The endocrine system regulates bodily
processes through hormones: substances
secreted by one set of cells that travel
through the bloodstream and affect the
activities of other cells.
• Each hormone affects only a select set of
cells, known as a hormone’s target cells.
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The Endocrine System
• Most hormones are produced and released
by endocrine glands, defined as glands that
secrete materials they have produced
directly into the bloodstream or surrounding
tissue.
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The Endocrine System
• Some hormones are produced not by
specialized glands, but by organs such as
the kidneys or the heart.
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Hormones and Target Cells
1. Endocrine cells
release hormone.
2. Hormone enters
circulation.
3. Hormone is
carried throughout the body.
Hormone will not
bind to cells that
are not target cells
4. Binding occurs;
receptor
hormonal effects
take place.
target cell
(skeletal muscle)
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Figure 28.1
pineal gland
hypothalamus
pituitary gland
parathyroid glands
(on posterior surface
of thyroid gland)
thyroid gland
thymus gland
cortex
adrenal
glands medulla
pancreas
testes
ovaries
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Figure 28.2
The Endocrine System
• Once secreted, hormones can take from several
seconds to several hours to work, but then can
continue to have effects for extended periods
of time.
• Given these timeframes, hormones tend to
regulate processes that unfold over minutes,
hours, or even years.
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28.2 Hormone Types and
Modes of Action
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Types of Hormones
• There are three principal classes of
hormones:
• amino-acid-based hormones
• peptide hormones
• steroid hormones
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Types of Hormones
• Each amino acid-based hormone is derived
from a chemical modification of a single
amino acid.
• Peptide hormones (by far the largest class of
hormones) are composed of amino acid
chains whose lengths can vary greatly.
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Types of Hormones
• Amino-acid-based and peptide hormones
generally link to their target cells via
receptors that protrude from the target cells’
outer or plasma membranes.
• This binding initiates a chain of chemical
reactions inside the cell that usually results
in the activation of one or more enzymes.
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Types of Hormones
• Steroid hormones generally pass through a
cell’s plasma membrane and bind with a
receptor protein inside the cell.
• The combined steroid hormone/receptor
molecule then binds with the cell’s DNA,
thus turning on one or more cell genes,
which results in the production of one or
more proteins.
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Types of Hormones
• Several steroid hormones, such as
testosterone and estrogen, are reproductive
hormones.
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The Endocrine System
Animation 27.2: The Endocrine System
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28.3 Negative Feedback and
Homeostasis
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How is Hormone Secretion
Controlled?
• Almost all hormone secretion is controlled
by negative feedback.
• With its many negative-feedback loops, the
endocrine system is important in preserving
homeostasis, meaning an organism’s
tendency to maintain a relatively stable
internal environment.
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28.4 Hormone Central: The
Hypothalamus
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How is Hormone Secretion
Controlled?
• Endocrine activity is largely governed by
the hypothalamus, which receives multiple
sensory inputs and in response controls the
release of multiple hormones.
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How is Hormone Secretion
Controlled?
•
The hypothalamus exercises endocrine
control by regulating hormonal release in
three separate organs:
•
•
•
The adrenal glands
The posterior pituitary gland
The anterior pituitary gland
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How is Hormone Secretion
Controlled?
• Nerve signals that the hypothalamus issues
to cells in the medulla of the adrenal glands
bring about the secretion of adrenaline and
noradrenaline.
• Oxytocin and vasopressin (synthesized in
the hypothalamus) are released into
circulation within the posterior pituitary
gland by axons extending from
hypothalamic neurons.
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How is Hormone Secretion
Controlled?
• Hormones released by the hypothalamus go
on to control the release of six hormones
produced by the anterior pituitary gland,
five of which go on to control the release
of hormones by other glands.
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hypothalamus
vasopressin
Controls retention
of water in the body
by the kidneys
kidneys
anterior
pituitary
prostate gland
in males
oxytocin
Stimulates contraction of
uterus muscles and release
of milk in females; assists in
semen ejaculation in males
posterior
pituitary
uterus and mammary
glands in females
medulla
cortex
adrenocorticotropic
hormone (ACTH)
Stimulates adrenal cortex
to secrete glucocorticoids,
which regulate energy use
thyroid-stimulating
hormone (TSH)
Triggers release of thyroid
hormones, which increase
metabolic rate
growth hormones (GH)
Stimulates growth by
prompting liver’s release of
somatomedin hormones
adrenaline + noradrenaline
adrenal gland
glucocorticoids
T3, T4 hormones
thyroid gland
bone, muscle,
other tissues
prolactin (PRL)
Stimulates mammary
gland development and
production of milk
mammary glands
follicle-stimulating
hormone (FSH)
Male: promotes
sperm production
Female: promotes egg
development; stimulates
ovaries to produce estrogen
luteinizing
hormone (LH)
Female: produces ovulation;
stimulates ovaries to produce
estrogen and progesterone
Male: stimulates testes to
produce androgens
testosterone
testes
estrogen
progesterone
ovaries
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Figure 28.6
28.5 Hormones in Action:
Three Examples
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Insulin and Glucagon
• The human body controls its circulating
levels of glucose through the use of two
hormones secreted in the pancreas:
• insulin, a hormone that reduces blood levels of
glucose
• glucagon, a hormone that increases blood levels
of glucose
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Insulin and Glucagon
• Insulin is produced by the pancreas’ beta
cells while glucagon is produced by its
alpha cells.
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Insulin and Glucagon
• After moving into circulation, insulin
prompts cells to create channels through
which they take in circulating glucose.
• In liver and skeletal muscle cells, some of
the glucose that is taken in may be stored in
the form of a molecule called glycogen.
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Insulin and Glucagon
• Glucagon prompts the transformation of
glycogen back into glucose in skeletal
muscle and liver cells.
• Diabetes results from a failure of the body
to move glucose into cells.
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(a) After a meal, the role of insulin
glucose
insulin
glycogen
glycogen
beta cell
glucose
channel
glucose
muscle cell
1. Pancreas: Stimulated by high
levels of glucose in the bloodstream, beta cells in the Islets
of Langerhans produce insulin.
2. Other cells throughout the
body: Insulin enables glucose
to move from the bloodstream
into cells by triggering the formation of channels in the cell
membranes.
liver cells
3. Skeletal muscle cells and liver cells: With insulin’s help, glucose
can move into these cells and either be used right away or stored
in the form of glycogen molecules.
(b) In between meals, the role of glucagon
glycogen
glucose
glycogen
glucose
glucose
glucagon
alpha cell
1. Pancreas: Stimulated by low
levels of glucose in the bloodstream, alpha cells in the
Islets of Langerhans produce
glucagon.
muscle cell
liver cells
2. Skeletal muscle cells and liver cells: With glucagon’s help,
glycogen is broken down into glucose. Muscle cells retain all
the glucose they derive from this process, using it to power
their own activities. Liver cells, meanwhile, move much of the
glucose they liberate into general circulation.
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3. Other cells throughout the
body: Glucose released by
the liver moves from the bloodstream into cells, supplying
them with energy.
Figure 28.8
Cortisol
• The hormone cortisol, released by the
adrenal glands, helps bring energy stores
into use but also is a “stress” hormone that
can have negative effects if stress goes on
for extended periods.
© 2011 Pearson Education, Inc.
Table 28.1
Hormones of the Endocrine System: Their Sources and Effects
Gland/Hormone
Effects
Hypothalamus
Releasing hormones
Inhibiting hormones
Stimulate hormone production in anterior pituitary
Reduce hormone production in anterior pituitary
Anterior pituitary
Thyroid-stimulating hormone (TSH)
Adrencorticotropic hormone (ACTH)
Follicle-stimulating hormone
Tiggers release of thyroid hormones
Stimulates adrenal cortex cells to secrete glucocorticoids
Female: promotes egg development; stimulates ovaries to produce estrogen
Male: promotes sperm production
Luteinizing hormone (LH)
Female: produces ovulation (egg release): stimulates ovaries to produce
estrogen and progesterone
Male: stimulates testes to produce androgens (e.g., testosterone)
Prolactin (PRL)
Stimulates mammary gland development and production of milk
Growth hormone (GH)
Stimulates growth by prompting liver’s release of somatomedin hormones
Posterior pituitary
Vasopressin
Oxytocin
Also known as antidiuretic hormone; controls retention of water in the body by
the kidneys
Stimulates contraction of the uterus muscles and release of milk in females;
assists in semen ejaculation in males
Thyroid
T 3, T 4
Calcitonin
Increase body’s metabolic rate
Reduces calcium ion levels in blood
Parathyroid
Parathyroid hormone (PTH)
Increases calcium ion levels in blood
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Table 28.1 (1 of 2)
Table 28.1
Table 28.1
Hormones of the Endocrine System: Their Sources and Effects
Gland/Hormone
Effects
Thymus
Thymosins
Stimulate development of white blood cells (Iymphocytes) in early life
Adrenal cortex
Glucocorticoids
Mineralocorticoids
Includes cortisol, which stimulates glucose production and breakdown of fats;
a stress-response hormone
Cause the kidneys to retain sodium ions and water and excrete potassium ions
Adrenal medulla
Adrenaline
Noradrenaline
Also known as epinephrine; stimulates release of energy stores; increases
heart rate and blood pressure
Also known as norepinephrine; effects similar to adrenaline
Pancreas
Insulin
Decreases glucose level in blood
Glucagon
Increases glucose level in blood
Testes
Testosterone
Ovaries
Estrogens
Progesterones
Pineal gland
Melatonin
Promotes production of sperm and development of male sex characteristics
Support egg development, growth of uterine lining, and development of
female sex characteristics
Prepare uterus for arrival of developing embryo and support of further
embryonic development
Establishes day/night cycle
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Table 28.1 (2 of 2)