CHAPTER 46: THE ENDOCRINE SYSTEM
WHERE DOES IT ALL FIT IN?
Chapter 46 builds on the foundations of Chapter 32 and provides detailed information about animal
form and function Students should be encouraged to recall the principles of eukaryotic cell structure
and evolution associated with the particular features of animal cells. Multicellularity should also be
reviewed. The information in chapter 46 does not stand alone and fits in with the all of the chapters
on animals. Students should know that animals and other organisms are interrelated and originated
from a common ancestor of all living creatures on Earth.
SYNOPSIS
Chemical hormones are produced by ductless endocrine glands and are transported to the target
organ through the blood. Their actions are broadly based and have long term effects, contrary to
the localized, short-term effects of the nervous system. Receptor proteins in the target organs
respond to the appropriate chemical messenger and trigger changes in cell activity. Some
hormones, like steroid hormones, enter the cell and bind to receptors within the cell’s cytoplasm,
altering gene activity. Others, like peptide hormones, do not enter the cell and bind to receptors
embedded in the cell membrane. Many hormones require second messengers like cAMP and
IP3/Ca++ to effect their molecular message. Multiple second messengers allow for varied control
of each hormonal system. For example, the antagonistic actions of epinephrine and insulin on
liver cells. Epinephrine uses cAMP as a second messenger, effecting a conversion of glycogen to
glucose. Obviously, insulin cannot use the same second messenger on the same cells to illicit the
conversion of glucose to glycogen.
Many endocrine functions are controlled by the hypothalamus. The posterior lobe of the pituitary
is connected to the hypothalamus by neurons. Antidiuretic hormone (ADH or vasopressin) and
oxytocin are produced in the hypothalamus and transported to the posterior pituitary through
these neurons. The hormones are then released from the posterior pituitary into the general
circulation. Oxytocin prepares the female body for childbirth and nursing, while ADH helps
regulate water reabsorption by the kidneys.
The anterior pituitary is connected to the hypothalamus by short blood vessels through which
hypothalamic releasing factors are transported. These releasing hormones stimulate the anterior
pituitary to produce specific tropic hormones. The seven hormones are: growth hormone (GH or
somatotropin), adrenocorticotropic hormone (ACTH), thyroidstimulating hormone (TSH),
luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), and melanocytestimulating hormone (MSH). Three of these, GH, PRL, and MSH, are controlled by antagonistic
action. Another hormone is produced to inhibit the secretion of the pituitary hormone:
somatostatin inhibits GH, PIH inhibits prolactin, and MIH inhibits MSH. TSH, LH, FSH, and
ACTH are controlled by negative feedback from the target glands. Each hormone itself inhibits
production of its own releasing hormone.
The thyroid gland produces thyroxine, which increases oxidative respiration and promotes
growth in children. It also produces calcitonin, which stimulates the uptake of Ca++ from the
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blood to the bones. Parathyroid hormone (PTH) is produced by the four, small parathyroid
glands and has a greater involvement with calcium uptake and regulation. Along with
aldosterone, it is one of the two hormones that is absolutely essential for survival. PTH is
released when the blood Ca++ gets too low as it is necessary for contraction of all muscles as well
as proper nerve function. The adrenal gland produces four hormones, two in the medulla and two
in the cortex. The medullary hormones, epinephrine and norepinephrine, provide a long lasting
alarm response similar to that of the sympathetic nervous system fight or flight response. The
cortical hormones, cortisol and aldosterone, stimulate carbohydrate metabolism and regulate
blood salt levels, respectively. The pancreas is both endocrine and exocrine in function and
regulates blood sugar levels through the balanced secretion of insulin and glucagon. These
hormones are produced by the beta and alpha cells, respectively, in the islets of Langerhans.
Hormones are produced by several other organs including the ovaries and testes (sex hormones),
pineal gland (melatonin), heart (atrial natriuretic hormone), kidneys (erythropoietin), and even
the skin. By definition, vitamin D, produced in the skin and carried to the intestine where it
stimulates absorption of calcium, is a hormone too. Molting and metamorphosis in insects is
influenced by the secretion of ecdysone and juvenile hormones. Both hormones are required for
molting. If the level of juvenile hormone is high, the molt produces yet another larva, but if its
level is low, as it is at the end of metamorphosis, a pupa is produced.
CHAPTER OBJECTIVES
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Compare the action of a typical hormone with that of a neuron.
Know the four chemical classes of molecular messengers and how each operates.
Define paracrine regulation and give several examples.
Understand the two primary mechanisms of hormone action associated with whether or not the
hormone itself enters the cell proper.
Differentiate between the actions of the cAMP and IP3/Ca++ second messenger systems.
Identify and describe the functions of the hormones that are released by the posterior pituitary
gland. Know where these hormones are synthesized.
Identify and describe the effects of the hormones that are released by the anterior pituitary gland.
Know what stimulates their production and where they are produced.
Understand how the regulation of GH, PRL, and MSH differs from that of TSH, ACTH, LH, and
FSH.
Describe and give an example of negative feedback inhibition in the endocrine system.
Know what hormones are produced by the thyroid and what each does.
Know the function(s) of PTH and in which endocrine gland this hormone is produced.
Describe the anatomical and endocrinological division of the adrenal gland, the hormones
produced and their function(s).
Know why the pancreas is both an endocrine and exocrine gland and how its secretions are
involved with the regulation of blood glucose.
Identify and describe the actions of several hormones produced by organs not commonly
considered to be endocrine glands.
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COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 46 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students believe that all hormones are steroids
Students confuse the mechanisms of lipophilic and hydrophilic hormone action
Students think that all animals evolved at about the same time
Students believe that animals can sense emotions and danger
Students believe that only humans have a well-developed endocrine system
Students are unaware of the genetic conservation of animal hormones
Students believe that most animals are vertebrates
Students do not equate humans with being animals
Students believe that all animals have identical organ system structures
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
Stress that the neuroendocrine system is still under the control of the central nervous system and
is dependent on signals from sensory neurons. The action of the neuroendocrine system differs
from that of the sympathetic neurons in terms of duration and spectrum. Tiny amounts of
chemicals in the blood are circulated to multitudes of target cells and are active until degraded.
This requires a relatively small expenditure of raw materials and energy. To sustain continued
sympathetic action would require great amounts of energy with continual nervous activity. Each
hormone has an apparent profound effect on a few body organs and less noticeable effects on
many organs. Such subtle effects of the major hormones continue to be discovered as
biochemical and molecular techniques improve. Indeed, if the connection between the brain and
a target organ were simple and singular, the control would likely be relegated to the nervous
system. A great many interactions exist for which science is not yet aware. To remember which
hormone controls which aspect of blood glucose, glucagon is made when blood “glucose is
gone.”
Discuss the care with which exogenous hormones and mimics (steroids, oral contraceptives,
insulin) must be used to prevent upset of natural body hormones. Those controlled by feedback
loops are frequently most affected.
Oxytocin is often used to treat esophageal impactions (choke) in horses. The usual treatment is
surgery, quite dangerous and not always successful. Although oxytocin causes smooth muscle,
present in the lower third of the esophagus, to contract, the upper tow-thirds of the esophagus in
horses is striated, voluntary muscle. Oxytocin causes this muscle to relax, the blockage clears on
its own or is readily manipulated by the veterinarian. (Equus, March 1998)
Explain why insulin may not be taken by pill form versus why the hormones for contraception
can be taken by pill form.
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HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 46.
Application
Analysis
Synthesis
Evaluation
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Have students describe the similarities of endocrine system and nervous
system cellular communication.
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Have students explain why hormones can flow to every cell in the body
and yet only affect particular cells.
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Ask students to explain why certain chemicals can cause the same effects
as hormones.
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Have students explain the differences and similarities between lipophlic
and hydrophilic hormone action.
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Have students explain the consequences of damage to the pancreas that
reduces hormone production.
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Ask students analyze the pros and cons using insulin injections to replace
the role of insulin in people with diabetes mellitus.
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Ask students to design an experiment to test the effects of giving growth
hormone injections to slow down the aging process in mammals.
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Have students design an experiment to test if certain pollutants compete
with estrogen for the estrogen receptor.
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Ask the students come up with a commercial use of molting hormone in
insects.
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Ask students evaluate the claims that plant hormones can be used to
supplement deficiencies in human hormones.
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Ask students evaluate the effectiveness of using pig insulin to treat people
with diabetes mellitus.
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Ask students evaluate the accuracy of using fish to study endocrine
regulation in humans.
VISUAL RESOURCES
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Obtain a brain model and point out the location, size, and relationship of the pituitary gland to
the hypothalamus.
Use diagrams and models different animals to show the similarities and differences in endocrine
system organs.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Hormone Feedback Review
Introduction
This demonstration uses animations to help students review feedback related two
antagonistic hormones. It was developed by the British Broadcasting Corporation for K-12;
however, many of the animations are appropriate for reviewing general biology concepts.
Materials
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Computer with Media Player and Internet access
LCD hooked up to computer
Web browser linked to BBC Animations website at
http://www.bbc.co.uk/schools/gcsebitesize/teachers/biology/activities.shtml
Procedure & Inquiry
1. Ask the class what they know about endocrine system feedback of blood sugar.
2. Load up the BBC website and click on the following links in the sequence below.
a. Insulin synthesis
b. Osmoregulation
c. Glucoregulation
3. Have students review the concepts after each sequence.
4. Ask the students to briefly explain what other endocrine system feedback systems use
antagonistic hormones.
USEFUL INTERNET RESOURCES
1. Colorado State University has a valuable endocrinology website for supplementing
lectures with animated diagrams of endocrine system function. The site is available at
http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/index.html
2. Computer modeling plays a strong role in understanding endocrine system function.
Students can be shown a computer based investigation of hormone chemistry on the IBM
research website. The website has various biological molecule demonstrations. The
website is available at:
http://www.zurich.ibm.com/deepcomputing/scientific/projects_biochem.html.
3. Faculty and students will find value in websites that simplify animal anatomy and
physiology concepts. The information can be used for projects that educate children and
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civic groups about animals. Biology-4-kids is a model website for animal education. The
website can be found at http://www.biology4kids.com/files/systems_nervous.html.
4. Case studies are an effective tool for stimulating interest in a lesson on animals. The
University of Buffalo has a case study called “A Case of Diabetes Insipidus” which has
students investigating the endocrinology of a little-known disorder that is often confused
with diabetes mellitus. The case study can be found at
http://www.sciencecases.org/diabetes_insipidus/diabetes_insipidus.asp.
LABORATORY IDEAS
A. Comparative Endocrinology
This activity has students has students use a human endocrine system diagram to look at
the similarities and differences of endocrine system organization in other vertebrates.
a. Explain to the students that all vertebrates evolved from fish-like ancestors and carry out
similar endocrine functions. However, do explain that there may be some evolutionary
differences.
b. Then explain that they will be looking for endocrine organs in a fish and frog using a
human endocrine system chart as a guide.
c. Provide students with the following materials:
a. Detailed diagram of human endocrine system
b. Preserved specimen of fish
c. Preserved specimen of frog
d. Dissecting equipment
e. Dissecting microscope
d. Instruct students to use the human endocrine system chart to try to identify the endocrine
system components of a fish and a frog.
e. Have them record the ease of using the human diagram to do this for each specimen. Use
their observations as a discussion point for the degree of difference and similarity in
vertebrate endocrine systems.
LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students do a lesson do a hands-on program on the animal homeostasis for
elementary students.
2. Have students tutor high school students studying animal anatomy and physiology.
3. Have students volunteer on environmental restoration projects with a local conservation
group.
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4. Have students volunteer at the educational center of a zoo or marine park.
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