SECTION 29.6
29.6
Plan and Prepare
Objectives
The Endocrine System
and Hormones
KEY CONCEPT
The endocrine system produces hormones that affect growth,
development, and homeostasis.
• Describe how hormones influence
the activities of a cell.
• Describe the major endocrine glands
and the hormones they produce.
• Explain the role of the hypothalamus.
• Identify some endocrine diseases,
their causes, and effects.
MAIN IDEAS
VOCABULARY
• Hormones influence a cell’s activities by entering the
cell or binding to its membrane.
• Endocrine glands secrete hormones that act
throughout the body.
• The hypothalamus interacts with the nervous and
endocrine systems.
• Hormonal imbalances can cause serious illness.
Section Resources
hormone, p. 896
gland, p. 896
hypothalamus, p. 898
pituitary gland, p. 898
releasing hormones, p. 900
Unit Resource Book
Study Guide pp. 43–44
Power Notes p. 45
Reinforcement p. 46
Pre-AP Activity pp. 51–52
Connect If you hear a loud BANG, your brain tells your body that you could be in
danger. You might need to run away or defend yourself. Your brain alerts your
endocrine system to send out chemicals that will speed up your heart rate,
increase blood flow to your muscles, and get you ready for action.
Interactive Reader Chapter 29
Spanish Study Guide pp. 299–300
Hormones influence a cell’s activities by entering
the cell or binding to its membrane.
MAIN IDEA
Biology Toolkit pp. C6, C13, C19,
C38, C39
The endocrine system makes chemical signals that help the body grow, develop, and maintain homeostasis. Some of these chemicals control processes
such as cell division, cell death, and sexual development. Others help you
maintain homeostasis by affecting body temperature, alertness, or salt levels.
The chemical signals made by the endocrine system are
target
called hormones. Hormones are made in organs called glands,
which are found in many different areas of the body. Glands
horrelease hormones into the bloodstream, as shown in
FIGURE 29.18. As a hormone moves through the body, it
bloodstream
comes into contact with many different cells. But it will
interact only with a cell that has specific membrane
receptors. If the hormone touches a cell that does not have
a matching receptor, nothing happens. If it touches a cell
that has the correct receptors, it binds to the cell and
receptor
not a target
prompts the cell to make certain proteins or enzymes. Cells
that have receptors for a hormone are called the target cells
of that hormone.
All hormones belong to one of two categories: steroid hormones and
FIGURE 29.18 Glands release
nonsteroid hormones. All steroid hormones are made of cholesterol, a type of
hormones into the bloodstream,
but hormones will only affect
lipid. On the other hand, there are three types of nonsteroid hormones that
cells that have receptors for those
are made up of one or more amino acids.
hormones.
Technology
Power Presentation 29.6
Media Gallery DVD
Online Quiz 29.6
Activate Prior Knowledge Have
students think about how their bodies
have changed over the past ten years.
Ask, What is the main cause of the
changes associated with young adults?
hormones Tell students that in this
section they will be learning about the
endocrine system, which is responsible
for releasing those hormones.
Teach
Vocabulary
Greek and Latin Word Origins The
root of the word hormone is the Greek
hormon, meaning “to urge on.”
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Have students use the Directed ReadingThinking Activity for this section. Students
skim the text to preview the material and
then use a four-column chart to list what
they know, what they think they know, what
they need to find out, and what was learned.
Biology Toolkit, DRTA, p. C6
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As FIGURE 29.19 shows, steroid hormones and nonsteroid hormones influence cells’ activities in different ways. A steroid hormone can enter its target
cells by diffusing through the cell membrane. Once inside, the steroid hormone attaches to a receptor protein, which transports the protein into the
nucleus. After it is inside, the steroid hormone binds to the cell’s DNA. This
binding causes the cell to produce the proteins that are coded by that portion
of DNA.
Nonsteroid hormones do not enter their target cells. These hormones bind
to protein receptors on a cell’s membrane and cause chemical reactions to take
place inside the cell. When nonsteroid hormones bind to receptors, the receptors change chemically. This change activates molecules inside the cell. These
molecules, called second messengers, react with still other molecules inside the
cell. The products of these reactions might initiate other chemical reactions in
the cell or activate a gene in the nucleus.
Connecting
CONCEPTS
Connecting
Cell Membrane Recall from
Chapter 3 that cell membranes
are made of a phospholipid
bilayer. Only some molecules,
such as steroid hormones, can
diffuse through it.
outside
Cell Membrane The phospholipid
molecules of a cell membrane have their
nonpolar heads facing the outside and
inside surfaces of the cell membrane,
with their polar tails hidden inside the
membrane. Nonpolar substances such as
steroid hormones are not repelled by
the nonpolar cell membrane, so they can
enter the cell.
inside
ligand
receptor
TEACH FROM VISUALS
A Apply Why do hormones only affect some cells?
FIGURE 29.19 Hormone Action
Steroid hormones enter the cell, but nonsteroid hormones do not.
STEROID HORMONE
1
steroid hormone
2
receptor
nucleus
NONSTEROID HORMONE
Steroid hormone
diffuses through the
cell membrane.
3
Steroid hormone
binds to a receptor
within the cell.
The hormone and
receptor enter the
nucleus and bind
to DNA.
INTERACTS
WITH
MEMBRANE
1
GETS MESSAGE
INTO CELL
CAUSES
CHEMICAL
REACTIONS
non-steroid
hormone
Nonsteroid hormone
binds to receptor on
the cell membrane.
2
receptor
Receptor stimulates
a second messenger
within the cell.
3
second messenger
Second messenger starts
a series of chemical reactions in the cytoplasm.
nucleus
CONCEPTS
FIGURE 29.19 Have students compare
both sides of the figure and point out
the alignment of one side to the other.
Ask
• Where does the steroid hormone
meet a receptor? within the cell the
nonsteroid hormone? outside the
cell
• How does the reaction caused by
the steroid hormone differ from the
nonsteroid hormone? Steroid
hormone acts on DNA to produce
its product; nonsteroid hormone
produces a chemical reaction in the
cytoplasm.
• Which type of hormone is more
likely to produce an immediate
effect and why? nonsteroid hormone, one that does not require
DNA to go through protein synthesis
chemical
reactions
DNA
4
Steroid hormone
causes DNA to
make proteins.
MAKES
PRODUCTS
4
Answers
Second messenger
reactions activate
enzymes.
proteins
activated enzymes
B Contrast How do the ways in which steroid and nonsteroid hormones affect a cell differ?
Chapter 29: Nervous and Endocrine Systems
9:28:54 AM
PRE-AP
ENGLISH LEARNERS
Tell students that the hormone commonly
referred to as adrenaline (epinephrine) is a
nonsteroid hormone. Adrenaline moves
quickly into the bloodstream to contribute to
the body’s response when a person feels
threatened or frightened. Have students take
five minutes to write about whether there is
a selective advantage in having a hormone
associated with the fight-or-flight response
be nonsteroidal.
Use the diagrams in FIGURE 29.19 to help
students visualize what is happening at each
numbered step. Use questions to help bring
out the detail of the diagrams. Then suggest
students reformat each half of the diagram as
a sequence diagram, placing one diagram
above the other to make an easier comparison.
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A Apply Hormones will affect only
cells with matching receptors.
B Contrast Steroid hormones enter
cells and bind with receptors inside the
cells. The hormones and receptors then
enter the nucleus, causing DNA to make
proteins. Nonsteroid hormones bind
with receptors on the cells’ surface,
causing chemical reactions in the cells,
which activate enzymes.
Biology Toolkit, Sequence Diagram, p. C38
Biology Toolkit, Quick-Write, p. C19
Chapter 29: Nervous and Endocrine Systems 897
MAIN IDEA
Endocrine glands secrete hormones that act
throughout the body.
Teach continued
Vocabulary
Unlike the nervous system, the endocrine system does not have its own
connected network of tissues. However, its chemical messages can still travel
where they need to go. Hormones travel in the bloodstream to all areas of the
body to find target cells.
The endocrine system has many glands. Each gland makes hormones that
have target cells in many areas of the body. Some of these glands make hormones that prompt other endocrine glands to make and release their hormones. Other glands affect different body systems. Their hormones prompt
cells to divide or to take up nutrients. Other hormones keep the body’s blood
pressure within a set limit. Some of the major glands, along with a few of the
hormones that they make, are described below and in FIGURE 29.20.
Academic Vocabulary The words
secretion and secrete are distinct in
meaning from the words excretion
and excrete.
secretion, a substance produced and
used within the body
excretion, a product of bodily activity
released as waste
Both words come from similar roots,
meaning “to set aside” or “separate.”
1
The hypothalamus is a small area of the middle of the brain, as you
might recall from Section 29.4. It makes hormones that stimulate the
pituitary gland to release hormones. It also stimulates the production of
hormones that control growth, reproduction, and body temperature. You
will read more about the hypothalamus later in this section.
2
The pituitary gland is also in the middle of the brain. It makes and
releases hormones that control cell growth as well as osmoregulatory
hormones that regulate the concentration of water in the blood. Some
pituitary hormones stimulate the adrenals, thyroid, and gonads. The
pituitary also acts as a gateway through which hypothalamus hormones
pass before they enter the bloodstream.
3
The thyroid gland wraps around the windpipe on three sides. Its hormones regulate metabolism, growth, and development.
4
The thymus is in the chest. It makes hormones that cause white blood
cells to mature. It also stimulates white blood cells to fight off infection.
5
The adrenal glands are above the kidneys. The adrenals secrete hormones
that control the “fight or flight” response when stimulated by the parasympathetic nervous system. Adrenal hormones increase breathing rate,
blood pressure, and alertness.
6
The pancreas lies between the stomach and intestines. It makes digestive
enzymes as well as hormones that regulate how much glucose the body
stores and uses.
7
The gonads—ovaries in women and testes in men—make steroid hormones that influence sexual development and functions. Gonads of men
and women make the same hormones. However, men and women make
them in different amounts, which gives men and women different
sexual characteristics.
Take It Further
Hormones are especially potent
chemicals that can produce significant
effects, even when in low concentrations in the bloodstream. This is advantageous given that many hormones have
only a short time in which to act. Most
are quickly removed from the blood by
the kidneys or liver. The time a hormone
spends in the bloodstream is brief, from
1 to 30 minutes. In contrast, the time it
takes for the hormone’s effects to be
felt can vary widely—anywhere from
minutes to hours or days.
Answers
A Summarize Hypothalamus influences
growth, reproduction, and body
temperature. Pituitary influences water
balance and growth. Thyroid influences
metabolism, growth, and development.
Thymus influences the immune system.
Adrenal influences blood pressure and
breathing rate. Pancreas influences digestion and blood glucose levels. Gonads
influence sexual development and
functions.
Connecting
CONCEPTS
Reproduction You can read
more about how chemical signals in the body affect growth,
development, and reproduction
in Chapter 34.
A Summarize What body processes do each of the main endocrine
glands influence?
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Have students form pairs to think through
and answer the following questions:
• What would happen if an action potential
generated a response in the wrong motor
cell? The wrong part of the body would
respond.
• What would happen if a hormone’s signal
went to the wrong cell and why? Nothing
would happen because the cell lacks the
receptor.
898
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• How is a message
sent along
a neuron
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different from one sent by a hormone? The
neuron sends a chemical signal that runs
along a specific pathway; the hormone
sends a signal that goes wherever blood
flows.
Biology Toolkit, Think-Pair-Share, p. C13
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FIGURE 29.20 Glands and Some of the Major Hormones
Endocrine glands are found throughout the body, and they influence whole-body
processes. Some of the hormones they make are listed here.
1
2
ONLINE BIOLOGY Students can
graph cortisol levels and see how they
relate to time of day in Data Analysis in
Options for Inquiry on page 903.
HYPOTHALAMUS
• Growth hormone-releasing hormone (GHRH) causes the
pituitary to release growth hormone.
• Gonadotropin-releasing hormone (GnRH) causes gonads
to release hormones that control the reproductive system.
Integrating
Medical Science
PITUITARY
• Growth hormone (GH) stimulates cell division, protein
synthesis, and bone growth in multiple tissues.
• Antidiuretic hormone (ADH) causes the blood to absorb
water from the kidneys.
3
THYROID
4
THYMUS
5
ADRENAL GLANDS
6
PANCREAS
In 1988, while training for the Olympics
in Seoul, South Korea, American hurdler
Gail Devers began to have migraines,
sleeplessness, fainting spells, and vision
loss. She was diagnosed with Graves’
disease, a chronic disorder in which the
thyroid gland produces too much
thyroxin. When there is an increase in
the amount of thyroid hormone, a
person’s metabolism rate can be
increased by 60–100 percent.
As a result, Devers’s feet became swollen,
blistered, cracked, and painful. Doctors
thought her feet might have to be
amputated. However, with proper
treatment and determination, Devers
went on to win the Olympic gold for the
100-meter dash in 1992, and again in 1996.
• Thyroxin (T4) and Triiodothyronine (T3) increase metabolism, digestion, and a person’s energy levels.
• Calcitonin causes the body to remove calcium from the
blood and increase bone formation.
• Thymosin causes white blood cells to reproduce
and mature.
• Epinephrine causes the heart to increase its strength and
number of contractions, circulating blood more quickly.
• Insulin removes sugar from the bloodstream and increases
sugar metabolism.
• Glucagon increases sugar production and adds sugar to
the bloodstream.
7
FEMALE GONADS: OVARIES
7
MALE GONADS: TESTES
Take It Further
Tell students not to confuse the steroid
hormones that the body makes naturally
with anabolic-androgenic steroids that
some athletes use to enhance performance. Anabolic-androgenic steroids
are synthetic substances related to male
sex hormones. They are sometimes
prescribed medically to treat delayed
puberty and to prevent wasting in
patients with AIDS. However, abuse of
these steroids can lead to liver disease,
blood clots, aggression, and irritability.
• Estrogen causes sexual maturation, including egg production, and influences female characteristics, such as fat distribution and widening of the hips.
• Progesterone causes menstruation.
• Testosterone causes sexual maturation, including sperm
production, and male characteristics, such as facial hair
and a deep voice.
A CRITICAL Why is the bloodstream a good means for transporting
VIEWING hormones such as growth hormone and calcitonin?
Chapter 29: Nervous and Endocrine Systems
899
Answers
9:29:10 AM
PRE-AP
INCLUSION
Have students study FIGURE 29.20, then close
their books. Ask them to draw a rough outline
of the human body in their science notebook.
Have them locate and identify as many
endocrine glands as they can. Ask students if
they see any parallels between the general
placements of the endocrine system and that
of the central nervous system. centralized
location along the main axis of body, close to
most major organs
Provide students who are visually impaired
with a cutout of the human body. Have them
work with another student to add sticker
dots where the endocrine glands are located.
The pair should identify the glands, the
hormones they secrete, and the effects of
those hormones.
bhspe-092906.indd Sec6:899
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A Critical Viewing Growth hormone
and calcitonin affect cells that are found
throughout the body. Because the
bloodstream reaches all parts of the
body, it can get hormones to their
target cells.
Chapter 29: Nervous and Endocrine Systems 899
MAIN IDEA
The hypothalamus interacts with the nervous
and endocrine systems.
Teach continued
TEACH FROM VISUALS
FIGURE 29.21 Point out that the
hypothalamus connects the nervous
and endocrine systems. Ask
• What system is the hypothalamus
part of? both the endocrine and
central nervous systems
• What is the function of the hypothalamus in the CNS? It receives and
sorts impulses to other areas of the
brain.
• What type of signals does the
hypothalamus send? It produces
releasing hormones that then
activate other glands, such as the
pituitary, to release their hormones.
The nervous and endocrine systems connect to each other at the base of the
brain, where the hypothalamus acts as a part of both systems. As part of the
CNS, it receives, sorts, and interprets information from sensory organs. As
part of the endocrine system, the hypothalamus produces releasing hormones
that affect tissues and other endocrine glands. Releasing hormones
are hormones that stimulate other glands to release their hormones.
Many of the hypothalamus’s releasing hormones affect the pituitary gland. These glands can quickly pass hormones back and forth
to each other. A series of short blood vessels connects the two, as you
can see in FIGURE 29.21. These two glands work together to regulate
various body processes. When the nervous system stimulates the
hypothalamus, it releases hormones, which travel to the pituitary.
Together, the hypothalamus and pituitary regulate many processes.
The diagram below shows how releasing hormones help glands to
“talk with” one another to maintain body temperature.
pituitary
gland
hypothalamus
blood flow
pituitary
gland
1
When the body becomes cold, thermoreceptors
in the nervous system send a signal that stimulates the hypothalamus.
2
The hypothalamus responds to this stimulus by
secreting a releasing hormone called TRH (TSHreleasing hormone).
hypothalamus
TRH travels through a short blood vessel and
stimulates the pituitary to release TSH (thyroidstimulating hormone).
pituitary
TSH travels through the bloodstream to the neck,
where it stimulates the thyroid to release thyroxine, a hormone that increases cells’ activity.
thyroid
FIGURE 29.21 The hypothalamus
stimulates the pituitary to secrete
hormones into the bloodstream.
Take It Further
3
Prostaglandins are hormonelike lipids
that regulate cell activities. Unlike
hormones, they are not produced by
specific endocrine glands. Instead, they
are produced by many cells throughout
the body and act locally. Prostaglandins
help regulate blood pressure, childbirth,
blood clotting, and the body’s inflammatory response to infection.
4
A
COLD EXPOSURE
stop
TRH
TSH
BB
A
thyroxine
5
As cells become more active, the body’s temperature increases. Thermoreceptors signal the
hypothalamus to stop releasing TRH. In the
absence of TRH, the other glands are no longer
BODY WARMS
stimulated. One by one, they stop releasing their
hormones, and the cycle is turned off.
Notice that releasing hormones, such as TRH and TSH, act as a type of
feedback on the glands they target. In Chapter 28, you learned that a feedback
is something that stimulates a change. As long as releasing hormones are
present, each target gland will continue to make more and more hormones.
However, when the body reaches its ideal temperature, the hypothalamus
stops releasing TRH. Then the pituitary and the thyroid stop releasing their
hormones too.
Answers
A Analyze The hypothalamus receives
nerve impulses from the brain and other
parts of the body. It also releases
regulating hormones, which cause other
endocrine glands to release hormones.
A Analyze How does the hypothalamus connect the nervous and endocrine systems?
ONLINE BIOLOGY The interactive
animation in Options for Inquiry,
page 903, examines what happens when
an imbalance occurs in a hormone
feedback loop.
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Have students create a cycle diagram for the
feedback loop shown on page 900. Suggest
they overlay the diagram onto an outline of
the human body, placing the hypothalamus,
pituitary, and thyroid in their approximate
locations.
Biology Toolkit, Cycle Diagram, p. C39
900
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MAIN IDEA
History of Science
Hormonal imbalances can cause severe illness.
A
On the other hand, in Addison’s disease the adrenal glands do not make
enough cortisol. Usually, Addison’s disease occurs because the immune system
attacks the adrenal glands. The disease causes loss of appetite, weight loss, and
low blood pressure. Although hormonal imbalances can cause serious illnesses
and may even be fatal, many hormonal imbalances can be treated with surgery
or medicine.
BB
Cushing’s syndrome is named after
Dr. Harvey Williams Cushing, an early
pioneer in neurosurgery. The syndrome
is a disorder of the adrenal cortex,
caused by a pituitary tumor. Cushing was
among the first to treat such disorders
surgically. He used surgery to treat
acromegaly, a disease in which the
pituitary gland releases too much
growth hormone, producing enlarged
bone structures of the face, hands,
and feet.
Because hormones play an important role in maintaining homeostasis, too
much or too little of a hormone will affect the entire body. In Chapter 28, you
learned that diabetes occurs when the pancreas does not make the right
amounts of insulin and glucagon, hormones that regulate sugar concentration
in the blood. When other glands do not function properly, a person may get
other diseases. For example, if the thyroid does not make enough hormones, a
person will develop hypothyroidism. In children, this condition slows growth
and mental development. In adults, hypothyroidism causes weakness, sensitivity to cold, weight gain, and depression. Hyperthyroidism, or the condition of
having too many thyroid hormones, produces opposite symptoms.
The wrong amount of adrenal hormones also affects the entire body.
Cortisol is an adrenal hormone that helps the body break down and use sugars
and control blood flow and pressure. If the adrenal glands produce too much
cortisol, the body cannot metabolize sugars properly, and a person can develop Cushing’s syndrome. This syndrome causes obesity, high blood pressure,
diabetes, and muscle weakness. It occurs when the pituitary, which releases
hormones that stimulate the adrenal glands, is not working the way it should.
Steroids, a pituitary tumor, or some prescription drugs can make the pituitary
overactive and indirectly cause Cushing’s syndrome.
Answers
A Infer The pituitary gland releases
hormones that stimulate organs that are
part of other body systems.
CHI6
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To learn more about the endrocrine system, visit scilinks.org.
Keycode: MLB029
Assess and Reteach
A Infer Why might a problem with a person’s pituitary gland lead to problems in
Assess Use the Online Quiz or Section
Quiz (Assessment Book, p. 576).
Reteach Make a three-column chart on
the board. Title the first column Glands,
the second Hormones, and the third
Function. Have students supply the
information for the chart, copying it into
their notebooks.
other body systems?
29.6
ONLINE QUIZ
ASSESS MENT
REVIEWING
MAIN IDEAS
1. What determines whether a
particular hormone will act on a
target cell?
2. What two main hormones does the
pituitary gland produce?
3. How do releasing hormones of the
hypothalamus connect the nervous and endocrine systems?
4. Why do hormonal imbalances
affect the entire body?
ClassZone.com
CRITICAL THINKING
5. Predict How might your body
be affected if a certain gland
made too much releasing hormone
that stimulates the thyroid? What
if it made too little releasing
hormone?
6. Apply What two body systems
does the endocrine system rely
on to generate and transport signals?
29.6 ASSESSMENT
00.2
ASSESSMENT
1. A hormone
will act on a cell only if the cell
has the proper receptor.
b10hspe-092906.indd
901
2. growth hormone and osmoregulatory
hormones
3. Releasing hormones are the chemical
messages that the hypothalamus releases in
response to the impulses it receives from
the nervous system.
Connecting
CONCEPTS
7. Cell Biology Steroid hormones
are made of cholesterol, which
is a type of lipid. Using what you
know about cell membranes,
why do you think steroids can
diffuse into a cell, while nonsteroid hormones cannot?
Chapter 29: Nervous and Endocrine Systems
901
4. Hormones play an important role in
6. nervous and circulatory systems
maintaining homeostasis.
7. Because the cell membrane is a lipid-bilayer,
PM
5. Too little of the releasing hormone would9/2/08 2:02:15lipid
molecules, such as steroid hormones,
result in too little thyroid activity, which
can pass through the membrane. Nonlipid
leads to weakness, sensitivity to cold,
molecules, such as nonsteroid hormones,
weight gain, depression, and memory loss.
cannot pass through the membrane.
Too much of the releasing hormone would
produce opposite effects.
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