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36–3 The Integumentary System
Section 36–3
1 FOCUS
Objectives
“G
ood fences make good neighbors,” wrote the American
poet Robert Frost as he explained the importance of
property boundaries. Living things have their own “fences,” and
none is as important as the skin—the boundary that separates
the human body from the outside world.
The skin, the single largest organ of the body, is part of the
integumentary (in-teg-yoo-MEN-tuh-ree) system. The word
integument comes from a Latin word that means “to cover,”
reflecting the fact that the skin and its related structures form
a covering over the entire body. Skin and its related structures—
the hair, nails, and a variety of glands—make up the integumentary system.
The Skin
The skin has many different functions, but its most important
function is protection.
The integumentary system
serves as a barrier against infection and injury, helps to
regulate body temperature, removes waste products
from the body, and provides protection against ultraviolet radiation from the sun. Because the largest component of
the integumentary system—the skin—contains several types of
sensory receptors, it serves as the gateway through which
sensations such as pressure, heat, cold, and pain are transmitted to the nervous system.
The skin is made up of two main layers—the epidermis and
the dermis. Beneath the dermis is a subcutaneous layer of fat
(the hypodermis) and loose connective tissue that help insulate
the body.
Key Concept
• What are the functions of the
integumentary system?
36.3.1 State the functions of the
integumentary system.
36.3.2 Describe the structure of
hair and nails.
Vocabulary
epidermis
keratin
melanin
dermis
hair follicle
Vocabulary Preview
Reading Strategy:
Building Vocabulary
Before you read, preview
Figure 36–13 to identify
vocabulary with which you are
unfamiliar. As you read, look
for the meaning of these terms.
Before students read the section,
suggest that they preview new
Vocabulary by finding each
Vocabulary word in the section and
reading its definition.
Reading Strategy
Call students’ attention to the Key
Concept on this page that states the
functions of the integumentary system. Then, when they preview
Figure 36–13, have students predict
which structures are involved in each
function. As students read the section, they should note whether or
not their predictions were correct.
2 INSTRUCT
The Skin
Demonstration
(magnification: 340⫻)
Figure 36 –12
After
strenuous exercise, the skin
produces sweat, which
decreases the temperature
of the body and rids the body
of wastes. Sweat is secreted by
sweat glands and leaves the
body through sweat pores.
SECTION RESOURCES
Print:
Tim
r
• Teaching Resources, Lesson Plan 36–3,
Adapted Section Summary 36–3, Adapted
Sav36–3,
Worksheets 36–3, Section Summary
e
e
Worksheets 36–3, Section Review 36–3,
Enrichment
• Reading and Study Workbook A,
Section 36–3
• Lab Worksheets, Chapter 36 Real-World Lab
• Adapted Reading and Study Workbook B,
Section 36–3
Before class begins, cut an apple in
half. Tightly cover one half of the
apple with plastic wrap and leave the
other half exposed to the air. During
class, pass the two apple halves
around the room so that students
can inspect them. Then, ask: How do
the two apple halves differ? (The
cut surface of the unwrapped half has
started to turn brown and dry out. The
cut surface of the wrapped half is still
white and moist.) Based on your
observations, what role do you
think the skin of the apple plays?
(It protects the inside of the apple from
drying out and turning brown.) How
is the skin of an apple like human
skin? (Both protect what is inside.)
Technology:
• iText, Section 36–3
• Transparencies Plus, Section 36–3
Skeletal, Muscular, and Integumentary Systems
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36–3 (continued)
Page 934
FIGURE 36–13 STRUCTURE OF THE SKIN
The skin has an outer layer called the
epidermis and an inner layer called the
dermis. Predicting What is the function
of the dermis?
Epiphyte means “on the outside of
a plant.” It is a plant that grows on
another plant.
Nerves
Hair
Blood vessels
Sweat pore
Hair follicle
Sebaceous gland
Use Visuals
Figure 36–13 Have students use
the information in the figure to
make a chart comparing and contrasting the dermis and epidermis in
terms of their location and thickness
and the structures they contain.
(Student charts should show that the
epidermis is the thinner, outer layer of
skin through which hairs and pores
pass, and the dermis is the thicker,
inner layer of skin containing blood
vessels, nerve endings, muscles, hair
follicles, and sweat and sebaceous
glands.)
Epidermis
Dermis
Sweat gland
Hypodermis
Build Science Skills
Using Models Have students sketch
three simple cross-sectional models
of the epidermis. Then, have them
use their models to show how cells
in the epidermis are replaced. They
should modify the first sketch to
show skin cells dividing, the second
sketch to show skin cells moving
upward to the skin’s surface, and
the third sketch to show skin cells
being shed. Ask volunteers to share
their completed models with the
class.
Muscle
Epidermis comes from two Greek
words: epi, meaning “on the
outside,” and derma, meaning
“skin.” If the Greek word phyton
means “plant,” what does the
term epiphyte mean?
Fat
Epidermis The outer layer of the skin is the epidermis. The
epidermis has two layers. The outside of the epidermis—the part
that comes in contact with the environment—is made up of dead
cells. The inner layer of the epidermis is made up of living cells.
Cells in the inner layer of the epidermis undergo rapid cell
division, producing new cells that push older cells to the surface
of the skin. As they move upward, the older cells become flattened and their organelles disintegrate. They also begin making
keratin, a tough, fibrous protein.
Eventually, the keratin-producing cells die and form a
tough, flexible, waterproof covering on the surface of the skin.
This outer layer of dead cells is shed or washed away at a
surprising rate—once every four to five weeks.
The epidermis also contains melanocytes (MEL-uh-noh-syts).
Melanocytes are cells that produce melanin, a dark brown
pigment. Melanin helps protect the skin from damage by absorbing ultraviolet rays from the sun. Although most people have
roughly the same number of melanocytes in their skin, differences in skin color are caused by the different amount of melanin
the melanocytes produce and where these cells are distributed.
Look closely at Figure 36–13 and you will see that there are
no blood vessels in the epidermis. This explains why a slight
scratch will not cause bleeding.
What is melanin?
UNIVERSAL ACCESS
Inclusion/Special Needs
Help students appreciate the sensory abilities of
the skin. Have them close their eyes and try to
identify a familiar object by touch alone. Then,
have students experience pressure by pushing
the eraser end of a pencil against their palms.
Finally, have students touch a warm object such
as a heating pad and a cold object such as ice.
Discuss how these sensory abilities of the skin
could help protect the body from injury.
934
Chapter 36
Advanced Learners
Challenge students to investigate the relationship between body shape and temperature
regulation. (A lean, linear body shape has more
surface area of skin, relative to volume, and is better at losing heat; a short, stocky body shape has
less relative surface area of skin and is better at
retaining heat.) Ask students to explain the relationship in an oral report, illustrated with pictures
of people with different body shapes.
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Page 935
Address Misconceptions
Dermis The inner layer of the skin is the dermis. The dermis
Some students may think that people with dark skin do not need to
protect their skin from the sun or
that people who tan without burning are not damaging their skin
when they get darker in the summer.
Correct these misconceptions by
explaining that any skin can be damaged by exposure to sunlight.
Although melanin helps protect the
skin from sunlight, even people with
a lot of melanin in their skin can suffer sun damage.
lies beneath the epidermis and contains collagen fibers, blood
vessels, nerve endings, glands, sensory receptors, smooth
muscles, and hair follicles.
The skin interacts with other body systems to maintain
homeostasis by helping to regulate body temperature. When the
body needs to conserve heat on a cold day, the blood vessels in
the dermis narrow, helping to limit heat loss. On hot days, the
blood vessels widen, bringing heat from the body’s core to the
skin and increasing heat loss.
The dermis contains two major types of glands: sweat glands
and sebaceous (suh-BAY-shus), or oil, glands. If your body gets too
hot, sweat glands produce perspiration, or sweat. Sweat contains
water, salts, and other compounds. When sweat evaporates, it
takes heat away from your body. Sweat also gets rid of wastes from
the blood, along with water. In this way, the skin acts as an organ
of excretion. Sebaceous glands produce an oily secretion called
sebum. Sebum spreads out along the surface of the skin and
helps to keep the keratin-rich epidermis flexible and waterproof.
What structures are found in the dermis?
Protection From Sunburn
The UV Index and Sunburn
UV Index
Level
Ultraviolet (UV) radiation is one type of energy from
the sun. UV rays cause sunburn, some cataracts, and
skin cancer. There are many factors that affect the
amount of UV radiation to which you are exposed.
These include the time of day, the season, the
weather conditions, and your location. Recently, the
National Weather Service, the Environmental
Protection Agency, and the Centers for Disease
Control agreed upon a national UV index. The UV
index is issued daily to advise you of conditions in
your region of the country. Use the information in
the chart to answer the questions that follow.
Minimal
(0–2)
Apply sunscreen
Wear sunglasses near
snow and water
60
Low
(3–4)
Apply sunscreen
Wear sunglasses and hat
45
Moderate
(5–6)
Apply sunscreen
Wear sunglasses and hat
Apply lip balm
30
High
(7–9)
Apply sunscreen
Wear sunglasses and hat
Seek shade from 10 AM
to 4 PM
15
Very High
(10+)
Apply sunscreen
Wear sunglasses and hat
Avoid sun from 10 AM
to 4 PM
10
1. Interpreting Graphics Describe the trend in the
amount of time it takes to sunburn, from a minimal
UV index level to a very high UV index level.
2. Applying Concepts Why do you think applying
sunscreen is always recommended?
3. Drawing Conclusions Why should a hat worn
as protection against UV rays have a brim?
4. Predicting The minutes-to-burn data apply to
most people. What variable could cause the time
for a particular person to burn to be shorter or to
be longer?
How to Protect
Yourself
Minutes
to Burn
Call on students to give a definition
of the term UV index. (An indicator of
the strength of UV radiation based on
how long it takes skin to burn) Suggest
to students that they watch a televised weather report on a sunny day
and note how the UV index is reported
and what its value is.
Answers
1. The amount of time it takes to
burn decreases.
2. Because even low levels of UV
radiation can damage the skin
3. To protect the face and eyes
4. Amount of melanin in the skin
5. Graphs should have five bars of
decreasing height.
5. Using Tables and Graphs Use the data in the
table to construct a bar graph. Place the UV index
levels on the x-axis and the minutes to burn on the
y-axis.
Answers to . . .
Melanin is a brown pigment produced by melanocytes in the
epidermis.
FACTS AND FIGURES
Evolution of human skin color
Human skin color shows a gradual geographic
trend in Africa and Europe: Populations increasingly far from the equator tend to have less and
less melanin in their skin. Virtually all the hypotheses that have been proposed to account for this
trend assume that variation in the amount of
sunlight is the ultimate cause. One widely held
hypothesis states that darker skin is selected for at
lower latitudes because its higher melanin content
helps protect it from serious sunburn and skin
cancer, which can threaten survival. Another
hypothesis proposes that lighter skin is selected
for at higher latitudes because it can be penetrated by sunlight, which is needed to produce
vitamin D in deep layers of the skin. According to
this hypothesis, the extra vitamin D produced in
the skin of lighter-skinned people helps prevent
rickets, which can jeopardize female fertility by
causing pelvic deformities.
Collagen fibers, blood
vessels, nerve endings, glands, sensory
receptors, smooth muscles, and hair
follicles
Figure 36–13 Based on structures
located in the dermis, students may
predict that the dermis produces sweat
and oil, controls growth of hair, and is
responsible for detecting sense stimuli
such as touch.
Skeletal, Muscular, and Integumentary Systems
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Skin Cancer Excessive exposure to the ultraviolet radiation
in sunlight can produce skin cancer, an abnormal growth of cells
in the skin. You can help protect yourself from this dangerous
disease by wearing a hat, sunglasses, and protective clothing
whenever you plan to spend time outside. In addition, you
should always use a sunscreen with a sun protection factor
(SPF) of at least 15.
36–3 (continued)
Hair and Nails
Build Science Skills
Designing Experiments Point out
to students that many different factors—such as age, gender, general
health status, genetic background,
some diseases, and certain medications—can affect the pattern and
rate of hair growth. Challenge students to design an experiment to
measure the effects of one particular
factor on hair growth. Call on students to give a brief description of
their experimental design, including
the hypothesis they would test. Ask:
Which variable would you investigate and which variables would
you control? (Students should investigate one variable, such as age or
gender, and control, or hold constant,
any other variables believed to affect
hair growth, such as certain illnesses
or medications.)
3 ASSESS
Evaluate Understanding
Hair and Nails
The basic structure of human hair and nails is keratin. In other
animals, keratin forms a variety of structures, including bull
horns, reptile scales, bird feathers, and porcupine quills.
왖
Figure 36–14 In this colorenhanced scanning electron
micrograph of a hair shaft, the
scalelike structures are layers of skin
cells. The part of the hair that is
above the skin is made up of dead
cells that become filled with keratin.
Observing What layer of the skin
contains the hair follicle?
Call on several students at random
to name the functions of the skin.
Hair Hair covers almost every exposed surface of the body and
has important functions. Hair on the head protects the scalp
from ultraviolet light from the sun and provides insulation from
the cold. Hairs in the nostrils, external ear canals, and around
the eyes (eyelashes) prevent dirt and other particles from
entering the body.
Hair is produced by cells at the base of structures called hair
follicles. Hair follicles are tubelike pockets of epidermal cells
that extend into the dermis. The individual hair shown in
Figure 36 –14 is actually a large column of cells that have filled
with keratin and then died. Rapid cell growth at the base of the
hair follicle causes the hair to grow longer. Hair follicles are in
close contact with sebaceous glands. The oily secretions of these
glands help maintain the condition of each individual hair.
Nails Nails grow from an area of rapidly dividing cells known
as the nail root. The nail root is located near the tips of the
fingers and toes. During cell division, the cells of the nail root fill
with keratin and produce a tough, platelike nail that covers and
protects the tips of the fingers and toes. Nails grow at an average rate of 3 millimeters per month, with fingernails growing
more rapidly than toenails—about four times as fast.
Reteach
Have students define or describe the
function of each of the structures of
the skin that are shown in Figure
36–13.
36–3 Section Assessment
1.
Some of the topics students might
address are the outer waterproof
coverings; the roles of the guard
cells and sweat and oil glands; trichomes and nails; and the roles of
root hair cells and human hair.
Similarities include the cuticle in
plants and the keratin in skin.
Key Concept List the
functions of the integumentary
system.
2. What organs and tissues make up
the integumentary system?
3. Compare the structures of the
epidermis and dermis.
5. In what way is the growth of hair
and nails similar?
6. Critical Thinking Applying
Concepts Why does cutting
your skin hurt, but cutting your
hair or nails does not hurt?
4. How does the skin help maintain
body temperature?
Structure and Function
Compare and contrast the
structure and function of the
dermal tissue in plants
discussed in Chapter 23 with
the structures in human skin.
In what ways are they similar?
Hint: You may wish to organize your ideas in a Venn
diagram.
36–3 Section Assessment
If your class subscribes to the iText,
use it to review the Key Concepts in
Section 36–3.
Answer to . . .
Figure 36–14 The dermis contains
the hair follicle.
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Chapter 36
1. Serves as a barrier against infection and
injury, helps regulate body temperature,
removes waste products, protects against UV
radiation, and allows sensory input
2. Skin, hair, nails, and glands
3. The epidermis, the outer, thinner layer,
contains melanin and has a surface layer of
dead cells. The dermis, the inner, thicker
layer, contains blood vessels, nerves,
glands, sense organs, muscles, and hair
follicles.
4. Blood vessels in the dermis narrow to conserve heat and widen to increase heat loss.
Evaporation of sweat also causes heat loss.
5. Both grow from an area of rapidly dividing
cells at the base of the hair or nail.
6. The dermis contains nerves; hair and nails
have no nerves.