SECTION
CHAPTER 28
Human Systems and Homeostasis
28.1
LEVELS OF ORGANIZATION
Study Guide
KEY CONCEPT
The human body has five levels of organization.
VOCABULARY
determination
differentiation
tissue
organ
organ system
MAIN IDEA: Specialized cells develop from a single zygote.
Fill in the main idea and supporting information for cell development.
1. Stem cells:
2. Determination
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3. Differentiation
4. What are the characteristics of stem cells?
5. Look at Figure 28.2. Describe some of the shapes and structures that the cells in this
figure acquired during differentiation.
6. Give two examples of how cell structures relate to cell functions.
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CHAPTER 28
Human Systems and Homeostasis
STUDY GUIDE, CONTINUED
MAIN IDEA: Specialized cells function together in tissues, organs, organ systems,
and the whole organism.
7. Write a description of each level of organization and draw a sketch to help you
remember it.
Description
Sketch
Vocabulary Check
8. There is an easy way to remember the difference between determination and
differentiation. Look at the first part of each word. Explain how these word parts can
help you remember the meaning of each term.
2
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Level of Organization
SECTION
CHAPTER 28
Human Systems and Homeostasis
28.1
LEVELS OF ORGANIZATION
Power Notes
Steps in Cell Specialization
1.
can become any of 200
types of cells in human body.
5. Examples:
2.
4.
3. Example:
Five Levels of Organization
10.
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Definition:
9.
Definition:
8.
Definition:
7.
Definition:
6.
Definition:
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CHAPTER 28
Human Systems and Homeostasis
SECTION
28.1
LEVELS OF ORGANIZATION
Reinforcement
KEY CONCEPT The human body has five levels of organization.
Humans, like all multicellular organisms, are made up of specialized cells that work
together. These cells arise from a single cell, the zygote, which divides to form embryonic
stem cells. Stem cells can become any one of more than 200 different types of cells. Cell
specialization involves determination and differentiation.
Determination occurs when stem cells commit to become only one type of cell, such
as a muscle cell. Committed cells still retain all the genetic information needed to build
an entire organism. Differentiation is the process by which committed cells acquire the
structures and functions of highly specialized cells. For example, a skeletal muscle cell
acquires a nucleus and a long body. Programmed cell death, or apoptosis, is also an
important part of developing individual structures such as individual fingers or toes.
The human body has five levels of organization.
• Specialized cells are characterized by their specific structures and functions.
• A tissue is a group of similar cells that work together to perform a specialized
function. Four tissue types are epithelial, connective, muscle, and nervous tissue.
• An organ is a structure composed of different types of tissues that function together.
• An organ system is two or more organs working together in a coordinated way.
• An organism is made up of all the organ systems that work together to support life.
What affects one organ or organ systems can affect all organs or organ systems. The
human body is made up of 11 organ systems.
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1. Which kind of cells can become any type of cell in the body?
2. What is the difference between determination and differentiation?
3. Label each item in the list below according to its level of organization.
Item
Level of Organization
lungs
heart and blood vessels
red blood cells
skeletal muscle
human being
4
Reinforcement
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SECTION
Study Guide
KEY CONCEPT
Homeostasis is the regulation
and maintenance of the internal
environment.
MAIN IDEA:
CHAPTER 28
Human Systems and Homeostasis
28.2
MECHANISMS OF HOMEOSTASIS
VOCABULARY
homeostasis
feedback
negative feedback
positive feedback
Conditions within the body must remain within a narrow range.
1. Give two reasons why it is so important that the internal environment of the body
remains stable.
2. Homeostasis is maintained by control systems. Fill in the name and function of the parts
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of the control system in the cycle diagram below.
Sensors
Control center
Targets
Communication system
3. What might happen if a target organ cannot respond?
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CHAPTER 28
Human Systems and Homeostasis
STUDY GUIDE, CONTINUED
MAIN IDEA:
Negative feedback loops are necessary for homeostasis.
4. Study the following line drawings. Which of the following diagrams represents negative
feedback and which represents positive feedback? Explain your answer.
A.
B.
5. It’s a hot day and you’re sweating. Is this response an example of a positive or negative
feedback loop? Explain your answer.
Explain briefly how your control systems act to bring more oxygen into your body.
Vocabulary Check
7. What is the difference between positive and negative feedback loops?
8. Think of an analogy that would illustrate the process of feedback for someone who does
not know what the word means.
6
Study Guide
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6. When you run, your muscles require more oxygen as their level of activity increases.
SECTION
CHAPTER 28
Human Systems and Homeostasis
28.2
MECHANISMS OF HOMEOSTASIS
Power Notes
Control Systems and Feedback Loops
Control center’s function:
Target’s function:
Communication system’s function:
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Sensor’s function:
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CHAPTER 28
Human Systems and Homeostasis
SECTION
28.2
MECHANISMS OF HOMEOSTASIS
Reinforcement
KEY CONCEPT Homeostasis is the regulation and maintenance of the internal
environment.
Conditions within the body must remain within the narrow limits that support life. These
conditions include fluid balance, internal body temperature, levels of trace minerals,
and so on. Homeostasis is the regulation and maintenance of the internal environment.
The body has many control systems that keep its internal environment stable. Control
systems are composed of four parts.
• Sensors gather information about internal and external conditions. For example,
sensors in the skin gather information about air temperature.
• A control center receives information from the sensors, compares it to set points, or
ideal values, and responds by sending messages through a communication system.
• The nervous and endocrine systems act as communication systems. Nerve impulses
or hormones are messages sent to targets throughout the body.
• Targets are organs, tissues, or cells that respond to messages.
The parts of a control system work together in what is known as a feedback loop.
Feedback is information from sensors that allows a control center to compare current
conditions to a set of ideal values. Negative feedback loops counteract any change
that moves conditions above or below a set point. For instance, if your fluid balance
falls below a set point, your brain sends signals that cause you to drink more. Positive
feedback loops increase change away from set points. In an emergency, for example,
adrenaline pours into your system to give you more strength until the emergency is over.
2. Name the four parts of a control system.
3. Your stomach is growling in hunger. Is this signal part of a positive or negative feedback
loop? Explain.
4. A friend tells you that people can hold their breath until they die. Use your knowledge
of homeostasis and control systems to explain why this is highly unlikely to happen.
8
Reinforcement
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1. What is homeostasis?
SECTION
Study Guide
KEY CONCEPT
Systems interact to maintain homeostasis.
MAIN IDEA:
CHAPTER 28
Human Systems and Homeostasis
28.3
INTERACTIONS AMONG SYSTEMS
VOCABULARY
thermoregulation
Each organ affects other organ systems.
1. The organs in the body work together like members of a pit crew servicing a race car.
What other analogies can you think of to illustrate organ systems working together?
2. Fill in the table below to explain what each organ does to help produce vitamin D in
your body.
Organ
Function
Skin
Liver
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Kidneys
3. What role does the hypothalamus play to help regulate body temperature?
MAIN IDEA:
A disruption of homeostasis can be harmful.
4. List three reasons why homeostasis in the body might be disrupted.
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CHAPTER 28
Human Systems and Homeostasis
STUDY GUIDE, CONTINUED
5. Why is a long-term disruption of homeostasis usually more serious than a short-term
disruption?
Fill in the concept map to help you remember what you know about long-term and short-term
disruption of homeostasis.
Disruption of homeostasis
can be
9.
6.
usually leads to
10. damage to many organs over time
example
example
11.
8.
Vocabulary Check
11. Think of a diagram that might illustrate the term thermoregulation for someone
unfamiliar with the word. Use the space below to sketch your diagram.
10
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7.
can lead to
SECTION
CHAPTER 28
Human Systems and Homeostasis
28.3
INTERACTIONS AMONG SYSTEMS
Power Notes
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Organs Working Together: Thermoregulation
Sensors
Control Center
Function: Sensors in skin and blood vessels
detect a rise in temperature in the blood;
send information to control center.
Response:
Targets
Communication System
Response:
Function:
Disruption of Homeostasis
two types
1.
can produce these effects
2.
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3.
can produce these effects
4.
Power Notes
11
CHAPTER 28
Human Systems and Homeostasis
SECTION
28.3
INTERACTIONS AMONG SYSTEMS
Reinforcement
KEY CONCEPT Systems interact to maintain homeostasis.
In the human body, all of the organs interact with one another, regulated by feedback
mechanisms. Each organ system communicates with other organ systems through
chemical messages and nerve impulses. For example, in vitamin D production, the skin,
circulatory system, liver, kidneys, and endocrine system all work together to produce a
form of vitamin D the body can use to build strong bones. If any organ fails to do its
job, the level of vitamin D in the body decreases.
Interaction among organs is also important in thermoregulation. Maintaining a
steady internal body temperature requires the coordination of the skin, hypothalamus,
circulatory and respiratory systems, muscular system, and nervous and endocrine
systems. Sensors from the skin and blood vessels send information to the hypothalamus,
which then sends messages through the nervous and endocrine systems to the sweat
glands, respiratory and circulatory systems, and muscle systems.
Homeostasis can be disrupted for several reasons, such as change occurring too rapidly,
target organs failing to respond to signals, or disease changing the body’s chemistry. A
disruption of homeostasis can begin in one organ or organ system and result in a chain
reaction that affects other organs and organ systems. These effects can be short term
or long term. The common cold, for instance, will disrupt homeostasis for only a few
days. Chronic conditions such as diabetes, however, represent a long-term disruption
that can result in the failure of several organs.
2. How do organs and organ system communicate with one another?
3. What organ systems interact to maintain a steady internal body temperature?
4. What is the effect on the body of a short-term disruption of homeostasis? of a long-term
disruption?
12
Reinforcement
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1. Why it is important that organs and organ systems in the body work closely together?
CHAPTER
28
Data Analysis Practice
Many times a relationship between two variables becomes easy to see when data collected
from an experiment is graphed. Classifying the relationship between variables is part of data
analysis and drawing conclusions.
Sometimes athletes, such as triathletes and ultradistance runners, develop a condition in
which they do not have enough sodium (Na) after extreme physical exercise and a large
intake of fluids. Scientists wanted to understand more about how the low sodium condition
develops. They collected data on how the amount of extracellular sodium changed as athletes
at rest consumed fluids. Fluid retention levels were measured as changes in body weight (in
kilograms) of the athletes. The graph below shows the results of the study.
CHAPTER 28
Human Systems and Homeostasis
INTERPRETING GRAPHS: INVERSE RELATIONSHIPS
GRAPH 1. SODIUM CHANGE AND FLUID LEVELS
Sodium levels (mEq/L)
137
135
133
131
129
127
125
0
0
.5
1
1.5
2
2.5
Change in weight (kg)
3
Explain the relationship between sodium change and fluid levels (measured
as changes in body weight).
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1. Identify
2. Conclude Can you conclude that taking in large of fluids causes the amount of
sodium to lower? Why or why not?
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CHAPTER
Pre-AP* Activity
*Pre-AP is a registered trademark of the College Board, which was not involved in the
production of and does not endorse this product.
You have learned in Chapter 28 that embryonic stem cells become committed to developing
into a specific type of cell soon after the zygote is formed. This commitment, called cell
determination, takes place on a molecular level long before the observable changes of cell
differentiation occur.
MOLECULAR BASIS OF CELL DETERMINATION
CHAPTER 28
Human Systems and Homeostasis
28
DETERMINATION OF MUSCLE CELLS
How does an embryonic stem cell commit to becoming a muscle cell? Researchers have
identified several key muscle-determination genes. When one or more of these master
regulatory genes is expressed—that is, transcribed and translated––a stem cell becomes
committed to forming a skeletal muscle cell. One such master regulatory gene is myoD.
When myoD is expressed, the protein MyoD is produced. This protein is a powerful
transcription factor that binds to noncoding DNA and causes transcription of other regulatory
genes. These genes produce proteins that also act as transcription factors. At the end of the
chain of control proteins, genes that code for muscle proteins are transcribed and translated.
Experiments have shown that when MyoD protein is added to differentiated liver or fat
cells, they become muscle cells.
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MOLECULAR BASIS OF DIFFERENTIATION
Differentiation of a cell occurs when genes that code for tissue-specific proteins are
expressed. Tissue-specific proteins are found only in a certain kind of cell and give that cell
its characteristic structure and function. For example, skeletal muscle cells contain myosin
and actin, proteins that interact in muscle cells to make a muscle fiber contract. Myosin and
actin are muscle-specific proteins. Expression of the genes for myosin and actin occurs at
the end of the control-protein chain that begins with MyoD. The final control genes are
transcribed and translated. The committed cell, now called a myoblast, begins to produce
large quantities of muscle-specific proteins—myosin and actin. In a short time, the cell
is recognizable as a muscle cell.
CYTOPLASMIC DETERMINANTS
An obvious question that has not been answered about the formation of a muscle cell is
what causes the myoD gene to be expressed in the first place. What starts the determination
process in the early embryo? Scientists think that it all starts in the egg prior to fertilization.
The cytoplasm of an egg cell is not uniform. Organelles, proteins, and mRNA—called
maternal cytoplasmic determinants—are distributed unevenly in the egg. There may be a
large amount of a certain maternal protein in one area and none in another area. Organelles
may be clustered together in some regions but dispersed widely in others.
After the egg is fertilized, it begins to divide. As a result of the uneven distribution
of maternal cytoplasmic determinants, the nuclei in the daughter cells are surrounded by
different cytoplasmic environments. These differences play a critical role in determining
which genes will be expressed and what the fate of the cell will be.
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A second factor that plays an important role in determining what genes are expressed is the
interaction of cells in the developing embryo. An embryonic cell receives chemical signals
from the cells surrounding it. The signal molecules cause changes in the gene expression
in the target cell, a process called induction. These interactions among embryonic cells are
eventually responsible for the differentiation of all the different kinds of cells in the organism.
1. Create a sequence diagram showing how an uncommitted embryonic stem cell in a
zygote becomes a muscle cell in an embryo. Begin the flow diagram by showing the
factors that influence gene expression in an unfertilized egg cell, and end it with a
differentiated skeletal muscle cell. Use the labels Differentiation, Determination,
Cytoplasmic Determinants, and Induction in your diagram.
2. In vitro fertilization is a procedure in which human eggs are fertilized in a petri dish and
then implanted in a woman’s uterus so she can give birth to a baby. Human embryonic
cells become committed when the embryo has eight cells. What would happen if a cell
were removed from a four-cell embryo and implanted into a woman’s uterus? What
would happen if a cell were removed from a 32-cell embryo and implanted? Explain.
16
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CHAPTER 28
Human Systems and Homeostasis
INDUCTION
CHAPTER
Pre-AP Activity
Between the years of 1979 and 2002, 16,555 deaths in the United States were attributed to
exposure to excessive cold. These deaths resulted from the victims’ inability to maintain a
stable internal body temperature. In this activity you will learn how the human body regulates
body temperature, loses body heat to the environment, and why hypothermia occurs.
REGULATION OF BODY TEMPERATURE
To maintain homeostasis, the human body must be able to generate, retain, and discharge heat
depending on its activity level and the ambient (surrounding) temperature. The hypothalamus
regulates body temperature. It is sensitive to the smallest temperature changes in the blood
(0.5 °C) and nerve impulses received from the nerve endings in the skin. When body
temperature increases or decreases too much, the hypothalamus signals the body to respond.
Vasodilation increases blood flow to the surface of the skin. The average rate of cutaneous
blood flow is 300–500 mL/min, but vasodilation can increase it up to 3000 mL/min. This
increases heat loss. Vasoconstriction decreases blood flow to the periphery (arms, legs, skin,
muscle tissue) from 300–500 mL/min to 30 mL/min. This decreases heat loss from the body.
Shivering can increase surface heat production by 500 percent, but it is limited to a few hours
due to energy expenditure and fatigue. Sweat cools the body through evaporation. Behavioral
responses, such as increasing or decreasing activity levels, seeking shade, and adding or
removing layers of clothing, can also help.
CHAPTER 28
Human Systems and Homeostasis
28
THE DANGERS OF COLD EXPOSURE
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HEAT LOSS TO THE ENVIRONMENT
There are four main ways that the human body can lose heat to the environment: radiation,
conduction, convection, and evaporation. Body heat is lost through radiation when the
ambient temperature is lower than the temperature of the body, about 98.6 °F. Conduction
causes heat loss when the body is in direct contact with a colder object, allowing for the
molecular transference of heat energy. Conduction is 32 times greater in water than in air
due to water’s greater density. Convection is a form of conduction where an object or the
surrounding substance is in motion, as with the air blowing down from a ceiling fan. Heat is
lost through evaporation when water is converted from a liquid to a gas. If too much heat is
lost from the body and the internal temperature drops below 36.7 °C (98.2 °F), hypothermia
and death can occur.
HYPOTHERMIA
Hypothermia occurs when the internal body temperature decreases to a level where cerebral
and muscular function becomes impaired. As the core temperature drops, metabolic function
and oxygen consumption decrease. Hypothermia can be caused by cold temperatures,
inadequate clothing, wetness, fatigue, dehydration, and insufficient caloric intake. Caffeine
and alcohol consumption can also help cause or intensify hypothermia. Caffeine is a
diuretic which can increase dehydration; alcohol causes vasodilation and impairs shivering,
hypothalamic functioning, and awareness of one’s surroundings. The young and the elderly
are the most at risk for developing hypothermia. Young children are not able to generate as
much heat as adults and they lose heat more easily because they have a larger body surface in
relation to their total mass. The elderly have a lower metabolic rates, making it difficult for
them to generate heat and maintain a stable body temperature.
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CHAPTER 28
Human Systems and Homeostasis
1. To conserve body heat, vasoconstriction restricts blood flow to the periphery but not to
the body’s core. Explain how this is an adaptation for survival.
2. Suppose a mountain climber who has been climbing all day gets trapped on a cliff at
sunset. The winds start to pick up, so the climber sits down in an effort to shelter the
body. Cite three types of heat loss this mountain climber could experience.
3. It is not uncommon for people to become hypothermic even in locations with mild
weather. Explain a situation in which this is possible.
4. Suppose that while hiking you encounter a person you believe to be mildly or moderately
5. While treating the hypothermic individual, you remember that you have a thermos filled
with hot coffee in your backpack. Should you offer them some? Explain your reasoning.
18
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hypothermic. Identify four actions you could take to treat that individual.
CHAPTER
Vocabulary Practice
determination
organ
feedback
positive feedback
differentiation
organ system
negative feedback
thermoregulation
tissue
homeostasis
A. Words in Context Answer the questions to show your understanding of the
vocabulary words.
CHAPTER 28
Human Systems and Homeostasis
28
HUMAN SYSTEMS AND HOMEOSTASIS
1. Which of these two involves feedback: sensors providing information about oxygen
needs or oxygen entering red blood cells?
2. In thermoregulation, is a body maintaining a stable range of temperature or is it merely
producing an increase in temperature?
3. When you talk about an organ system are you talking about different organs working
together or different functions within an organ working together?
4. Would positive feedback or negative feedback increase changes away from set values?
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5. Which is more like homeostasis: an oven maintaining a set temperature or a pot of
water starting to boil?
6. When a lung cell has acquired hairlike cilia, has it gone through differentiation or
determination?
7. Is a muscle fiber an example of a tissue or an organ?
8. Is thermoregulation the process of maintaining a stable body temperature or of
producing body heat so cells can function?
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CHAPTER 28
Human Systems and Homeostasis
VOCABULARY PRACTICE, CONTINUED
B. Vector Vocabulary Define the words in the boxes. On each arrow, write a phrase that
describes how the words in the boxes are other.
1. DETERMINATION
2.
3.
More complex structures form.
4.
Similar cells work
together to perform
special functions.
8. HOMEOSTASIS
7.
Different organs work
together to perform
functions.
Conditions require change.
9.
20
Vocabulary Practice
Conditions maintained
despite change.
10.
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6.
C. Stepped-Out Vocabulary Define each word. Then write two additional facts
that are related to the word.
WORD
DEFINITION
MORE INFORMATION
Example feedback
information used to compare
current conditions to a set of
ideal values
negative and positive feedback loops
regulate change
most functions are regulated by
negative feedback
CHAPTER 28
Human Systems and Homeostasis
VOCABULARY PRACTICE, CONTINUED
1. differentiation
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3. organ
D. Categorize Words Write T next to words that can describe tissues. Write O next to
words that can describe organs. Write OS next to words that can describe organ systems.
1.
2.
muscle
all bones in the body
nerve
lung
skin
stomach lining
liver
heart
brain, spinal cord, nerves
blood
tendon
thymus, spleen, white blood cells
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CHAPTER 28
Human Systems and Homeostasis
VOCABULARY PRACTICE, CONTINUED
E. Who Am I? Choose among these terms to answer the riddles below:
determination
tissue
organ system
feedback
positive feedback
differentiation
organ
homeostasis
negative feedback
thermoregulation
1. I’m like a team: the players have different roles, but we’re all part of the same group.
2. When you ask someone to review your speech, you’ve asked for me.
3. I prevent your body from changing too much, like a guidance system that keeps a ship
on course.
4. My four different types make up every organ in the body.
5. If I’m not maintained, then critical processes in the body start breaking down.
6. I’m like a manager of a team giving each person special equipment to use.
7. When you get cut, you definitely want me there changing things quickly to stop the
bleeding.
Copyright © McDougal Littell/Houghton Mifflin Company.
F. Draw a Cartoon Draw a cartoon or diagram that illustrates three of the vocabulary
words, such as determination, differentiation, and tissue. You can include dialogue or a
caption for your cartoon.
22
Vocabulary Practice
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