1. Hormones and the Endocrine System
Chapter 26 Sec 1-3
Hormones and the Endocrine System

2. Introduction
In lions, the hormone testosterone promotes the development and maintenance of male traits including
growth and maintenance of the mane and
increased height and weight.
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3. The Nature of Chemical Regulation The Vertebrate Endocrine System
Figure 26.0_1
Chapter 26: Big Ideas
Hypothalamus
The Nature of Chemical Regulation
The Vertebrate Endocrine System
Figure 26.0_1 Chapter 26: Big Ideas
Hormones and Homeostasis 3

4. Figure 26.0_2
Figure 26.0_2 Phenotypic difference between the sexes (Panthera leo) 4

5. THE NATURE OF CHEMICAL REGULATION
THE NATURE OF CHEMICAL REGULATION
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6. 26.1 Chemical signals coordinate body functions
The endocrine system
consists of all hormone-secreting cells and
works with the nervous system in regulating body activities.
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The nervous and endocrine systems coordinate and regulate most other systems of the body. You might consider comparing the speed and duration of each system’s response. The nervous system generally responds faster but for a shorter duration than the endocrine system. This helps to explain why it takes many minutes for a person to calm down after a very upsetting event. The hormones do not clear quickly from the systems.
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7. 26.1 Chemical signals coordinate body functions
The nervous system also
communicates,
regulates, and
uses electrical signals via nerve cells.
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The nervous and endocrine systems coordinate and regulate most other systems of the body. You might consider comparing the speed and duration of each system’s response. The nervous system generally responds faster but for a shorter duration than the endocrine system. This helps to explain why it takes many minutes for a person to calm down after a very upsetting event. The hormones do not clear quickly from the systems.
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8. 26.1 Chemical signals coordinate body functions
Comparing the endocrine and nervous systems
The nervous system reacts faster.
The responses of the endocrine system last longer.
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The nervous and endocrine systems coordinate and regulate most other systems of the body. You might consider comparing the speed and duration of each system’s response. The nervous system generally responds faster but for a shorter duration than the endocrine system. This helps to explain why it takes many minutes for a person to calm down after a very upsetting event. The hormones do not clear quickly from the systems.
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9. 26.1 Chemical signals coordinate body functions
Hormones are
chemical signals,
produced by endocrine glands,
usually carried in the blood, and
responsible for specific changes in target cells.
Hormones may also be released from specialized nerve cells called neurosecretory cells.
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The nervous and endocrine systems coordinate and regulate most other systems of the body. You might consider comparing the speed and duration of each system’s response. The nervous system generally responds faster but for a shorter duration than the endocrine system. This helps to explain why it takes many minutes for a person to calm down after a very upsetting event. The hormones do not clear quickly from the systems.
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10. Endocrine cell Hormone molecules
Figure 26.1A
Secretory vesicles
Endocrine cell
Hormone molecules
Blood vessel
Figure 26.1A Hormone from an endocrine cell
Target cell 10

11. Neurotransmitter molecules
Figure 26.1B
Nerve cell
Nerve signals
Neurotransmitter molecules
Figure 26.1B Neurotransmitter from a nerve cell
Nerve cell 11

12. 26.2 Hormones affect target cells using two main signaling mechanisms
Two major classes of molecules function as hormones in vertebrates.
The first class includes hydrophilic (water-soluble), amino-acid-derived hormones. Among these are
proteins,
peptides, and
amines.
The second class of hormones are steroid hormones, which include small, hydrophobic molecules made from cholesterol.
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The two mechanisms by which hormones trigger changes in target cells can be compared using this analogy. If a house is like a cell, ringing the doorbell and having someone answer it is like using a signal-transduction pathway. Pushing the doorbell, like a hormone binding to plasma-membrane receptors, causes an internal change. Using steroid hormones, on the other hand, is like walking up to the house, opening the door, and walking inside to deliver a message. Here the signal passes through the surface and into the interior of the home/cell to directly communicate the message.
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13. 26.2 Hormones affect target cells using two main signaling mechanisms
Hormone signaling involves three key events:
reception,
signal transduction, and
response.
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The two mechanisms by which hormones trigger changes in target cells can be compared using this analogy. If a house is like a cell, ringing the doorbell and having someone answer it is like using a signal-transduction pathway. Pushing the doorbell, like a hormone binding to plasma-membrane receptors, causes an internal change. Using steroid hormones, on the other hand, is like walking up to the house, opening the door, and walking inside to deliver a message. Here the signal passes through the surface and into the interior of the home/cell to directly communicate the message.
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14. 26.2 Hormones affect target cells using two main signaling mechanisms
An amino-acid-derived hormone
binds to plasma-membrane receptors on target cells and
initiates a signal transduction pathway.
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The two mechanisms by which hormones trigger changes in target cells can be compared using this analogy. If a house is like a cell, ringing the doorbell and having someone answer it is like using a signal-transduction pathway. Pushing the doorbell, like a hormone binding to plasma-membrane receptors, causes an internal change. Using steroid hormones, on the other hand, is like walking up to the house, opening the door, and walking inside to deliver a message. Here the signal passes through the surface and into the interior of the home/cell to directly communicate the message.
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15. Animation: Water-Soluble Hormone
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The two mechanisms by which hormones trigger changes in target cells can be compared using this analogy. If a house is like a cell, ringing the doorbell and having someone answer it is like using a signal-transduction pathway. Pushing the doorbell, like a hormone binding to plasma-membrane receptors, causes an internal change. Using steroid hormones, on the other hand, is like walking up to the house, opening the door, and walking inside to deliver a message. Here the signal passes through the surface and into the interior of the home/cell to directly communicate the message.
Animation: Water-Soluble Hormone
Right click on animation / Click play
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16. Water-soluble hormone
Figure 26.2A_s1
Interstitial fluid
Water-soluble hormone
Receptor protein 1
Plasma membrane
Target cell
Figure 26.2A_s1 A hormone that binds a plasma membrane receptor (step 1)
Nucleus 16

17. Water-soluble hormone
Figure 26.2A_s2
Interstitial fluid
Water-soluble hormone
Receptor protein 1
Plasma membrane
Target cell 2
Signal transduction pathway
Relay molecules
Figure 26.2A_s2 A hormone that binds a plasma membrane receptor (step 2)
Nucleus 17

18. Water-soluble hormone
Figure 26.2A_s3
Interstitial fluid
Water-soluble hormone
Receptor protein 1
Plasma membrane
Target cell 2
Signal transduction pathway
Relay molecules
Figure 26.2A_s3 A hormone that binds a plasma membrane receptor (step 3) 3
Cellular responses
Cytoplasmic response or
Gene regulation
Nucleus 18

19. 26.2 Hormones affect target cells using two main signaling mechanisms
A steroid hormone can
diffuse through plasma membranes,
bind to a receptor protein in the cytoplasm or nucleus, and
form a hormone-receptor complex that carries out the transduction of the hormonal signal.
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The two mechanisms by which hormones trigger changes in target cells can be compared using this analogy. If a house is like a cell, ringing the doorbell and having someone answer it is like using a signal-transduction pathway. Pushing the doorbell, like a hormone binding to plasma-membrane receptors, causes an internal change. Using steroid hormones, on the other hand, is like walking up to the house, opening the door, and walking inside to deliver a message. Here the signal passes through the surface and into the interior of the home/cell to directly communicate the message.
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20. Animation: Lipid-Soluble Hormone
Student Misconceptions and Concerns
1. Student comprehension of the two mechanisms by which hormones trigger changes in target cells relies upon a good understanding of cell membranes and basic cellular chemistry. If these subjects have not been taught recently in your course, consider giving students a brief refresher before distinguishing between these mechanisms.
2. Students might not appreciate the diverse ways in which coordination and communication are achieved between the body’s cells. Endocrine signals generally work like a radio transmitter, sending signals outward. Only target cells, like people with radios tuned to a particular frequency, will receive the signal. In contrast, the nervous system provides a direct, two-way connection between the sender and receiver, much more like a land-based telephone call.
Teaching Tips
The two mechanisms by which hormones trigger changes in target cells can be compared using this analogy. If a house is like a cell, ringing the doorbell and having someone answer it is like using a signal-transduction pathway. Pushing the doorbell, like a hormone binding to plasma-membrane receptors, causes an internal change. Using steroid hormones, on the other hand, is like walking up to the house, opening the door, and walking inside to deliver a message. Here the signal passes through the surface and into the interior of the home/cell to directly communicate the message.
Animation: Lipid-Soluble Hormone
Right click on animation / Click play
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21. Interstitial fluid Steroid hormone Target cell Nucleus Figure 26.2B_s1
Figure 26.2B_s1 A hormone that binds an intracellular receptor (step 1) 21

22. Interstitial fluid Steroid hormone Target cell Receptor protein
Figure 26.2B_s2
Interstitial fluid
Steroid hormone 1
Target cell 2
Receptor protein
Nucleus
Figure 26.2B_s2 A hormone that binds an intracellular receptor (step 2) 22

23. Hormone- receptor complex
Figure 26.2B_s3
Interstitial fluid
Steroid hormone 1
Target cell 2
Receptor protein 3
Nucleus
Hormone- receptor complex
DNA
Figure 26.2B_s3 A hormone that binds an intracellular receptor (step 3) 23

24. Cellular response: activation of a gene and synthesis of new protein
Figure 26.2B_s4
Interstitial fluid
Steroid hormone 1
Target cell 2
Receptor protein 3
Nucleus
Hormone- receptor complex
DNA 4
Transcription
mRNA
Figure 26.2B_s4 A hormone that binds an intracellular receptor (step 4)
New protein
Cellular response: activation of a gene and synthesis of new protein 24

25. THE VERTEBRATE ENDOCRINE SYSTEM
THE VERTEBRATE ENDOCRINE SYSTEM
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26. 26.3 Overview: The vertebrate endocrine system consists of more than a dozen major glands
Some endocrine glands (such as the thyroid) primarily secrete hormones into the blood.
Other glands (such as the pancreas) have
endocrine and
nonendocrine functions.
Other organs (such as the stomach) are primarily nonendocrine but have some cells that secrete hormones.
Student Misconceptions and Concerns
Appreciating the precise actions of hormones requires a thorough understanding of the specificity of target cells. The fact that only certain target cells will respond to a given hormone signal allows hormones to be “broadcast” generally throughout the circulatory system without affecting every single cell.
Teaching Tips
Growth hormone levels typically decline as we age. Recent studies suggest that injections of engineered human growth hormone may promote muscle growth and decrease body fat. However, additional research is necessary to fully appreciate the potential benefits and risks of human growth hormone injections in the elderly.
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27. 26.3 Overview: The vertebrate endocrine system consists of more than a dozen major glands
The following figure shows the locations of the major endocrine glands.
Student Misconceptions and Concerns
Appreciating the precise actions of hormones requires a thorough understanding of the specificity of target cells. The fact that only certain target cells will respond to a given hormone signal allows hormones to be “broadcast” generally throughout the circulatory system without affecting every single cell.
Teaching Tips
Growth hormone levels typically decline as we age. Recent studies suggest that injections of engineered human growth hormone may promote muscle growth and decrease body fat. However, additional research is necessary to fully appreciate the potential benefits and risks of human growth hormone injections in the elderly.
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28. Ovaries (female) Testes (male)
Figure 26.3
Hypothalamus
Thyroid gland
Pituitary gland
Parathyroid glands (embedded within thyroid)
Thymus
Adrenal glands (atop kidneys)
Pancreas
Figure 26.3 The major endocrine glands in humans
Ovaries (female)
Testes (male) 28

29. 26.3 Overview: The vertebrate endocrine system consists of more than a dozen major glands
The following table summarizes the main hormones produced by the major endocrine glands and indicates how they
function and
are controlled.
Student Misconceptions and Concerns
Appreciating the precise actions of hormones requires a thorough understanding of the specificity of target cells. The fact that only certain target cells will respond to a given hormone signal allows hormones to be “broadcast” generally throughout the circulatory system without affecting every single cell.
Teaching Tips
Growth hormone levels typically decline as we age. Recent studies suggest that injections of engineered human growth hormone may promote muscle growth and decrease body fat. However, additional research is necessary to fully appreciate the potential benefits and risks of human growth hormone injections in the elderly.
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30. Table 26.3
Table 26.3 Major Human Endocrine Glands and Some of Their Hormones 30

31. Table 26.3_1
Table 26.3_1 Major Human Endocrine Glands and Some of their Hormones (Part 1) 31

32. Table 26.3_2
Table 26.3_2 Major Human Endocrine Glands and Some of their Hormones (Part 2) 32

33. 26.3 Overview: The vertebrate endocrine system consists of more than a dozen major glands
Two endocrine glands are not discussed further.
The pineal gland
is pea-sized, located near the center of the brain, and
secretes melatonin, a hormone that links environmental light conditions with biological rhythms.
The thymus gland
lies above the heart, under the breastbone, and
secretes a peptide that stimulates the development of T-cells.
Student Misconceptions and Concerns
Appreciating the precise actions of hormones requires a thorough understanding of the specificity of target cells. The fact that only certain target cells will respond to a given hormone signal allows hormones to be “broadcast” generally throughout the circulatory system without affecting every single cell.
Teaching Tips
Growth hormone levels typically decline as we age. Recent studies suggest that injections of engineered human growth hormone may promote muscle growth and decrease body fat. However, additional research is necessary to fully appreciate the potential benefits and risks of human growth hormone injections in the elderly.
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