SECTION 29.6 29.6 The Endocrine System - · PDF fileCell Membrane The phospholipid molecules...

Objectives• 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.

Section ResourcesUnit Resource Book

Study Guide pp. 43–44Power Notes p. 45Reinforcement p. 46Pre-AP Activity pp. 51–52

Interactive Reader Chapter 29Spanish Study Guide pp. 299–300

Biology Toolkit pp. C6, C13, C19, C38, C39

TechnologyPower Presentation 29.6Media Gallery DVDOnline 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.

VocabularyGreek and Latin Word Origins The root of the word hormone is the Greek hormon, meaning “to urge on.”

Plan and PreparePlan and Prepare

TeachTeach

U

target

not a target

FIGURE 29.18 Glands release hormones into the bloodstream, but hormones will only affect cells that have receptors for those hormones.

receptor

bloodstream

hor-

29.6 The Endocrine System and HormonesKEY CONCEPT The endocrine system produces hormones that affect growth, development, and homeostasis.

MAIN IDEAS• 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.

VOCABULARYhormone,hormone, p. 896

gland,gland, p. 896

hypothalamus,hypothalamus, p. 898

pituitary gland,pituitary gland, p. 898

releasing hormones,releasing hormones, p. 900

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.

MAIN IDEA

Hormones influence a cell’s activities by entering the cell or binding to its membrane.

The endocrine system makes chemical signals that help the body grow, de-velop, 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 called hormones.hormones. Hormones are made in organs called glands,glands,

which are found in many different areas of the body. Glands release hormones into the bloodstream, as shown in FIGURE 29.18. As a hormone moves through the body, it 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

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 nonsteroid hormones. All steroid hormones are made of cholesterol, a type of lipid. On the other hand, there are three types of nonsteroid hormones that are made up of one or more amino acids.

896 Unit 9: Human Biology

4.c Describe and differentiate among the organizational levels of organisms (e.g., cells, tissues, organs, systems, types of tissue).

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Differentiated Instruction

SECTION 29.6

BELOW LEVELHave students use the Directed Reading- Thinking 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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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.

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 hor-mone, one that does not require DNA to go through protein synthesis

AnswersA 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.

Connecting CONCEPTSConnecting CONCEPTS

TEACH FROM VISUALSTEACH FROM VISUALS

hormone,gland,hypothalamus,pituitary gland,releasing hormones,

hormones. glands,

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NONSTEROID HORMONESTEROID HORMONE

Steroid hormones enter the cell, but nonsteroid hormones do not.

FIGURE 29.19 Hormone Action

steroid hormone

receptor

non-steroid hormone

second messenger

Contrast How do the ways in which steroid and nonsteroid hormones affect a cell differ?

receptor

nucleus

nucleus

INTERACTS WITH

MEMBRANE

GETS MESSAGE INTO CELL

CAUSES CHEMICAL

REACTIONS

MAKES PRODUCTS

chemical reactions

1

2

3

1

DNA

proteinsactivated enzymes

2

3

4 4

ConnectingCell 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.

CONCEPTS

outside

ligand

inside

receptor

As FIGURE 29.19 shows, steroid hormones and nonsteroid hormones influ-ence cells’ activities in different ways. A steroid hormone can enter its targetcells by diffusing through the cell membrane. Once inside, the steroid hor-mone attaches to a receptor protein, which transports the protein into thenucleus. After it is inside, the steroid hormone binds to the cell’s DNA. Thisbinding causes the cell to produce the proteins that are coded by that portionof DNA.

Nonsteroid hormones do not enter their target cells. These hormones bindto protein receptors on a cell’s membrane and cause chemical reactions to takeplace inside the cell. When nonsteroid hormones bind to receptors, the recep-tors change chemically. This change activates molecules inside the cell. Thesemolecules, called second messengers, react with still other molecules inside thecell. The products of these reactions might initiate other chemical reactions inthe cell or activate a gene in the nucleus.

Apply Why do hormones only affect some cells?

Steroid hormone binds to a receptor within the cell.

The hormone and receptor enter the nucleus and bind to DNA.

Steroid hormone causes DNA to make proteins.

Steroid hormone diffuses through the cell membrane.

Nonsteroid hormone binds to receptor on the cell membrane.

Receptor stimulates a second messenger within the cell.

Second messenger starts a series of chemical reac-tions in the cytoplasm.

Second messenger reactions activate enzymes.

Chapter 29: Nervous and Endocrine Systems 897

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B

PRE-APTell 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.

Biology Toolkit, Quick-Write, p. C19

ENGLISH LEARNERSUse 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.

Biology Toolkit, Sequence Diagram, p. C38


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VocabularyAcademic 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.”

Take It FurtherHormones are especially potent chemicals that can produce significant effects, even when in low concentra-tions in the bloodstream. This is advan-tageous 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.

AnswersA 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 diges-tion and blood glucose levels. Gonads influence sexual development and functions.

Teach continuedTeach continued

ConnectingReproduction You can read more about how chemical sig-nals in the body affect growth, development, and reproduction in Chapter 34.

CONCEPTS

MAIN IDEA

Endocrine glands secrete hormones that actthroughout the body.

Unlike the nervous system, the endocrine system does not have its ownconnected network of tissues. However, its chemical messages can still travelwhere they need to go. Hormones travel in the bloodstream to all areas of thebody to find target cells.

The endocrine system has many glands. Each gland makes hormones thathave target cells in many areas of the body. Some of these glands make hor-mones that prompt other endocrine glands to make and release their hor-mones. Other glands affect different body systems. Their hormones promptcells to divide or to take up nutrients. Other hormones keep the body’s bloodpressure within a set limit. Some of the major glands, along with a few of thehormones that they make, are described below and in FIGURE 29.20.

1 The hypothalamushypothalamus is a small area of the middle of the brain, as youmight recall from Section 29.4. It makes hormones that stimulate thepituitary gland to release hormones. It also stimulates the production ofhormones that control growth, reproduction, and body temperature. Youwill read more about the hypothalamus later in this section.

2 The pituitary glandpituitary gland is also in the middle of the brain. It makes andreleases hormones that control cell growth as well as osmoregulatoryhormones that regulate the concentration of water in the blood. Somepituitary hormones stimulate the adrenals, thyroid, and gonads. Thepituitary also acts as a gateway through which hypothalamus hormonespass before they enter the bloodstream.

3 The thyroid gland wraps around the windpipe on three sides. Its hor-mones regulate metabolism, growth, and development.

4 The thymus is in the chest. It makes hormones that cause white bloodcells to mature. It also stimulates white blood cells to fight off infection.

5 The adrenal glands are above the kidneys. The adrenals secrete hormonesthat control the “fight or flight” response when stimulated by the para-sympathetic nervous system. Adrenal hormones increase breathing rate,blood pressure, and alertness.

6 The pancreas lies between the stomach and intestines. It makes digestiveenzymes as well as hormones that regulate how much glucose the bodystores and uses.

7 The gonads—ovaries in women and testes in men—make steroid hor-mones that influence sexual development and functions. Gonads of menand women make the same hormones. However, men and women makethem in different amounts, which gives men and women differentsexual characteristics.

Summarize What body processes do each of the main endocrine glands influence?


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BELOW LEVELHave 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.

• How is a message sent along a neuron 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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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.

Integrating Medical ScienceIn 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.

Take It FurtherTell students not to confuse the steroid hormones that the body makes naturally with anabolic-androgenic steroids that some athletes use to enhance perfor-mance. 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.

AnswersA 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.

hypothalamus

pituitary gland

M9/06 9:29:10 AM

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.

1

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.

2

ADRENAL GLANDS• Epinephrine causes the heart to increase its strength and

number of contractions, circulating blood more quickly.

5

PANCREAS• Insulin removes sugar from the bloodstream and increases

sugar metabolism.• Glucagon increases sugar production and adds sugar to

the bloodstream.

6

THYMUS• Thymosin causes white blood cells to reproduce

and mature.

4

THYROID• Thyroxin (T4) and Triiodothyronine (T3) increase metabo-

lism, digestion, and a person’s energy levels.• Calcitonin causes the body to remove calcium from the

blood and increase bone formation.

3

FEMALE GONADS: OVARIES• Estrogen causes sexual maturation, including egg produc-

tion, and influences female characteristics, such as fat dis-tribution and widening of the hips.

• Progesterone causes menstruation.

7

MALE GONADS: TESTES• Testosterone causes sexual maturation, including sperm

production, and male characteristics, such as facial hair and a deep voice.

7

FIGURE 29.20 Glands and Some of the Major Hormones

Why is the bloodstream a good means for transporting hormones such as growth hormone and calcitonin?

Endocrine glands are found throughout the body, and they influence whole-body processes. Some of the hormones they make are listed here.

CRITICAL VIEWING


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PRE-APHave 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

INCLUSIONProvide 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.


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B

A

B

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 hypo-thalamus 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.

Take It FurtherProstaglandins 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 inflamma-tory response to infection.

AnswersA 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.

ONLINE BIOLOGY The interactive animation in Options for Inquiry, page 903, examines what happens when an imbalance occurs in a hormone feedback loop.

Teach continuedTeach continued

TEACH FROM VISUALSTEACH FROM VISUALS

hypothalamus

pituitary gland

FIGURE 29.21 The hypothalamus stimulates the pituitary to secrete hormones into the bloodstream.

blood flow

COLD EXPOSURE

BODY WARMS

hypothalamus

TRHTRH

pituitary

TSHTSH

pituitary gland

thyroxinethyroxine

stop

thyroid

MAIN IDEA

The hypothalamus interacts with the nervousand endocrine systems.

The nervous and endocrine systems connect to each other at the base of thebrain, where the hypothalamus acts as a part of both systems. As part of theCNS, it receives, sorts, and interprets information from sensory organs. Aspart of the endocrine system, the hypothalamus produces releasing hormones

that affect tissues and other endocrine glands. Releasing hormonesReleasing hormonesare hormones that stimulate other glands to release their hormones.

Many of the hypothalamus’s releasing hormones affect the pitu-itary gland. These glands can quickly pass hormones back and forthto each other. A series of short blood vessels connects the two, as youcan see in FIGURE 29.21. These two glands work together to regulatevarious body processes. When the nervous system stimulates thehypothalamus, 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.

1 When the body becomes cold, thermoreceptorsin the nervous system send a signal that stimu-lates the hypothalamus.

2 The hypothalamus responds to this stimulus bysecreting a releasing hormone called TRH (TSH-releasing hormone).

3 TRH travels through a short blood vessel andstimulates the pituitary to release TSH (thyroid-stimulating hormone).

4 TSH travels through the bloodstream to the neck,where it stimulates the thyroid to release thyrox-ine, a hormone that increases cells’ activity.

5 As cells become more active, the body’s tempera-ture increases. Thermoreceptors signal thehypothalamus to stop releasing TRH. In theabsence of TRH, the other glands are no longerstimulated. One by one, they stop releasing theirhormones, and the cycle is turned off.

Notice that releasing hormones, such as TRH and TSH, act as a type offeedback on the glands they target. In Chapter 28, you learned that a feedbackis something that stimulates a change. As long as releasing hormones arepresent, each target gland will continue to make more and more hormones.However, when the body reaches its ideal temperature, the hypothalamusstops releasing TRH. Then the pituitary and the thyroid stop releasing theirhormones too.

Analyze How does the hypothalamus connect the nervous and endocrine systems?


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hormone

pituitary gland releasing hormones

hypothalamus

gland

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BELOW LEVELHave 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


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00.2 ASSESSMENT

B

A

B

History of ScienceCushing’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.

AnswersA Infer The pituitary gland releases

hormones that stimulate organs that are part of other body systems.

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.

Assess and ReteachAssess and Reteach

29.6 ASSESSMENT

Connecting CONCEPTS

ONLINE QUIZClassZone.com

To learn more about the endro-crine system, visit scilinks.org.Keycode: MLB029

MAIN IDEA

Hormonal imbalances can cause severe illness.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, sensitiv-ity 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 de-velop 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.

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.

Infer Why might a problem with a person’s pituitary gland lead to problems in other body systems?

REVIEWING MAIN IDEAS

1. What determines whether a particular hormone hormone will act on a target cell?

2. What two main hormones does the pituitary gland pituitary gland produce?

3. How do releasing hormonesreleasing hormones of the hypothalamushypothalamus connect the ner-vous and endocrine systems?

4. Why do hormonal imbalances affect the entire body?

CRITICAL THINKING

5. Predict How might your body be affected if a certain glandgland 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?

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 non-steroid hormones cannot?


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29.6 ASSESSMENT 1. A hormone will act on a cell only if the cell

has the proper receptor. 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.

4. Hormones play an important role in maintaining homeostasis.

5. Too little of the releasing hormone would result in too little thyroid activity, which leads to weakness, sensitivity to cold, weight gain, depression, and memory loss. Too much of the releasing hormone would produce opposite effects.

6. nervous and circulatory systems 7. Because the cell membrane is a lipid-bilayer,

lipid molecules, such as steroid hormones, can pass through the membrane. Nonlipid molecules, such as nonsteroid hormones, cannot pass through the membrane.


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SECTION 29.6 29.6 The Endocrine System - · PDF fileCell Membrane The phospholipid molecules...

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