Download As you have learned, specialized cells are

3.3
As you have learned, specialized cells are organized into
tissues. For example, muscle tissue is made up of cells that
contract to help the body move. Nerve tissue is made up of
cells that carry signals to and from the brain. Tissues can
be classified into four major types. Figure 1 summarizes the
four major types of tissue.
Figure 1 The four major types of animal tissue
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Coverings, Connections, and Support
Two types of tissue, epithelial tissue and connective tissue, provide
coverings, connections, and support within the body.
Epithelial Tissue
Epithelial tissue (epithelium) is made up of
tightly packed cells that cover body surfaces
and line the body’s internal organs and cavities.
Epithelium can be a single layer of cells, or it can
be many layers of cells (Figure 2).
Epithelial tissue made up of a single layer of
cells allows materials to pass through the layer.
For example, it forms the air sacs of the lungs,
where oxygen is exchanged for carbon dioxide.
(a)
▶▶ epithelial tissue
(epithelium): sheets
of tightly packed cells
covering surfaces and
lining internal organs
(b)
Figure 2 Epithelium can be made up of (a) a single
layer of cells, or (b) many layers of cells.
Epithelium with many layers covers parts of the body that need
greater protection from injury. Human skin contains layers of
epithelial tissue. These cells help protect areas beneath the skin.
Connective Tissue
Connective tissue supports, protects, and connects the body’s
organs. Connective tissue is made up of both specialized cells and
non-living substances. Perhaps most surprising of all, blood is a
type of connective tissue. Blood connects body systems by bringing
oxygen and nutrients and removing wastes.
▶▶ connective tissue: tissue
composed of living cells
and non-living materials
that supports, protects,
and connects the body’s
organs
▶▶ bone: tissue made
up of living bone cells
surrounded by non-living
material
Bone and Other Connective Tissue
The most obvious type of connective tissue
is bone. Bone is made up of living bone cells
surrounded by hard, non-living material (Figure 3).
Bones are connected to each other by strong
elastic bands of connective tissue called ligaments.
Tough, inelastic connective tissue, called tendons,
attaches muscles to
bones. Between the
ends of the bones at
a joint, such as your
elbow, connective
Figure 3 Living bone
tissue called cartilage
cells are surrounded by
forms a cushioning pad
non-living bone.
(Figure 4).
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Figure 4 Connective tissues holds our tissues and
organs together.
3.3 Animal Tissues 73
Figure 5 The ACL is
located in the front of the
knee. When it becomes
torn, the knee becomes
less stable.
dig deeper
Did You Know?
Injuries on the Rise
Society’s interest in
physical fitness has
increased greatly. The
bad news is that doctors
are seeing more patients
with torn ACLs and other
connective tissue injuries.
▶▶ nerve tissue: specialized
tissue that makes up the
brain, nerves, and spinal
cord, and carries electric
signals to and from the
brain to control body
functions
Cartilage is also found in other parts of the body. You can feel
cartilage in your ears and nose. Cartilage cells are suspended in a
dense network of fibres that make the tissue strong, yet flexible.
Another type of connective tissue connects the skin to the muscles
and fat underneath.
Connective Tissue Injuries
Do you know anyone who has injured an Achilles tendon, had
tennis elbow, or suffered a torn ACL? A torn ACL is one of the most
common sports knee injuries. ACL stands for “anterior cruciate
ligament.” It is one of the ligaments holding the knee joint together.
Overstretching or suddenly twisting the knee can tear the ACL
(Figure 5). Repair often requires surgery.
Sensing and Responding
As you know, specialized cells in our ears, eyes, skin, nose, and mouth
help to collect information about our surroundings. The eye contains
light-sensitive cells. The ear contains hair cells that are sensitive to
sound vibrations. The tongue contains taste buds, and the nose has
cells that detect tastes and smells. The skin contains cells that respond
to temperature, touch, pain, and pressure. How is this information
carried to the brain? How do we respond to it? These are the tasks of
the other two types of tissue: nerve tissue and muscle tissue.
Nerve Tissue
nerve
connective
tissue
bundle of
nerve cells
nerve cell
Figure 6 Nerve cells
transmit signals around
the body.
If your hand gets close to something too hot, you pull your hand
away. Your body can feel because your skin contains millions of
nerve cells that make up nerve tissue. Nerve tissue is the most
complex tissue in the body. It makes up the brain, spinal cord,
and nerves. The brain is responsible for all thinking, language, and
memory, as well as directing routine body functions. Nerve tissue
transmits signals throughout the body (Figure 6).
There are three kinds of nerve cells. One kind of nerve carries
information from the body to the brain or spinal cord. These are
the nerves in your skin or sense organs that inform you about the
outside world. They are called sensory neurons. A second kind of
nerve carries instructions from the brain or spinal cord to another
body part—usually the muscles. These are called motor neurons.
The third kind of nerve connects the sensory and motor neurons
and are called interneurons. The brain and the spinal cord are made
up of interneurons.
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Let's say your hand gets close to a hot stove. The sensory
neurons in your hand sense the hot stove and send a signal to the
brain. The interneurons in your brain interpret the signal and send
a return signal to motor neurons in your arm and hand. The motor
neurons interact with the arm and hand muscles, making you pull
your hand away from the hot stove. All of this happens in less than
a second. The signals between your body and brain can travel very
fast. Some nerve signals can travel at more than 100 m/s!
Muscle Tissue
Muscle tissue is made up of cells that contract, or get shorter.
When each end of a muscle is attached to a different bone, the
contracting muscle pulls the two bones toward each other. This
allows us to move. Muscle tissue also enables the organs to
function. For example, heart muscle tissue allows the heart to pump
blood. Stomach muscle tissue allows the stomach to squeeze and
churn food to break it down.
▶▶ muscle tissue:
specialized tissue made
up of cells that shorten
or contract to allow
movement
There are three kinds of muscle tissue (Figure 7). Actions such as
walking or throwing a ball are voluntary. That means you decide to
move those body parts. The muscles that you control are skeletal
muscles. These muscles are made up of striated
muscle tissue.
Smooth muscle tissue is the second kind of
muscle tissue. Smooth muscle lines the walls
of arteries, veins, and body organs. Think about
when you eat. You cannot “tell” your stomach to
squeeze and churn the food you eat! It just does
so automatically. Smooth muscle is also called
involuntary muscle because it contracts and
relaxes without your conscious thought. This is
very important because if it were not involuntary,
we would spend all of our time thinking about
things like breathing and digesting food.
The third kind of muscle tissue is cardiac
muscle tissue. Cardiac muscle tissue is an
involuntary striated muscle that lines the walls
of the heart.
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Figure 7 The three types of muscle tissue: (a) striated;
(b) smooth; and (c) cardiac
3.3 Animal Tissues 75
Research This Multiple Sclerosis Research
Skills: Researching, Analyzing the Issue, Communicating, Evaluating
4.A., 4.B.
Imagine not being able to move your legs the way you
want to, or having a difficult time moving your mouth
the right way to form words. Multiple sclerosis (MS) is
a disease of the brain and spinal cord. In this disease,
the nerve cells are damaged. As a result, signals do
not travel smoothly between nerve cells. This can
cause a wide range of symptoms including vision
problems, numbness, tingling, and muscle weakness.
2.Research the incidence of MS in different
provinces and territories of Canada. Determine
if there are significant differences among the
provinces and territories.
The occurrence of this disease in Canada is very
high. In Crowsnest Pass, Alberta, for example, there
are 217 cases per 100 000 people. This is in contrast
to the South American rate of less than 30 cases
per 100 000.
A.Use a map of Canada to show the incidence of
MS in the different provinces and territories. T/ I 1.Research how MS affects people’s lives, including
the symptoms and how fast it progresses.
3.Find out what kind of research on MS is being
carried out in Canada and how this research might
benefit people with MS.
C
B.Write a summary of current MS research in
Canada. T/I C
C.Make a poster or draw a diagram that details the
different ways MS can affect the body, and how
new treatments might help. T/I C
go to Nelson Science
3.3 Wrap Up
• Epithelial tissue covers and lines parts of the body. Epithelial tissue is made
up of either a single layer of cells or many layers of cells.
• Connective tissue supports, protects, and connects the body’s organs. Bone
is specialized connective tissue that provides the body with support and
protection.
• Nerve tissue sends signals between the body and the brain. The brain
receives sensory information from the body and sends instructions to the
muscles.
• Muscle tissues enable movement. There are three kinds of muscle tissue:
striated, smooth, and cardiac muscle tissue.
Check Your Learning
1.List the four types of tissue and give an example
of each. Describe its function and where it can be
found. K/U C
2.Name and describe the three types of muscle.
Give an example of each type. K /U C
76 Chapter 3 • How the Body Works
3.How is connective tissue different from the other
kinds of tissues? Give an example. K/U C
4.Why is it important that some types of muscles
can contract and relax without our having to think
about it? K/U C
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