Structure and Movement The Skeletal System

Structure and Movement
The Skeletal System
Key Concepts
What do you think? Read the two statements below and decide
whether you agree or disagree with them. Place an A in the Before column
if you agree with the statement or a D if you disagree. After you’ve read
this lesson, reread the statements to see if you have changed your mind.
Before
Statement
After
1. Bones protect internal organs.
2. Bones do not change during a person’s
• What does the skeletal
system do?
• How do the parts of the
skeletal system work
together?
• How does the skeletal
system interact with other
body systems?
lifetime.
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Functions of the Skeletal System
Squeeze your hands and arms. The hard parts that you
feel are parts of your skeleton. When you think of your
skeleton, you probably think of bones. Your skeleton is part
of your skeletal system and is made up of more than 200
bones. The skeletal system contains bones as well as other
structures that connect and protect the bones and that support other
functions in the body.
Identify Main Ideas As you
read, highlight the functions
of the skeletal system. Use
another color to highlight
the different parts of a bone.
Your skeletal system performs several important functions.
It supports your body and helps you move. It protects the
organs in your body, such as your lungs and heart. The
skeletal system also makes and stores important materials
needed by your body.
Support
Imagine trying to stack cubes of gelatin. The gelatin cubes
would be hard to stack because they do not have any support
structures inside of them. Without bones, your body would
be like the gelatin cubes. Bones support your body. They help
you sit up and stand. They make it possible for you to lift
your legs to walk up stairs.
Reading Essentials
Reading Check
1. Explain How do bones
act as a support system?
Structure and Movement
225
Visual Check
2. Explain How does the
skeletal system help a person
play a musical instrument?
Movement
SCIENCE USE V. COMMON USE
tissue
Science Use a group of the
same type of cells that
perform a specific function
within an organism
Common Use a soft, thin
paper
Key Concept Check
3. Name the major
functions of the skeletal
system.
Protection
Feel the top of your head. The hard structure you feel is
your skull. The skull protects the soft tissue of your brain
from damage. Other bones help protect your spinal cord,
heart, lungs, and other organs in your body.
Production and Storage
Another function of your skeletal system is to make and
store materials needed by your body. Red blood cells are
produced inside some of your bones. Bones also store fat
and calcium. Calcium is a mineral needed for strong bones.
It is also used in many other cellular processes. When the
body needs calcium, it is released from the bones into the
blood.
Structure of Bones
A bone is an organ made of living tissue. There are two
main types of bone tissue: compact bone and spongy bone.
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Structure and Movement
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Different parts of your body can move in different ways
because of your skeletal system, as shown in the figure above.
Your knee bends when you kick a soccer ball. However, your
shoulders move in a different way when you raise your arms
to catch the same ball. Bones can move because they are
attached to muscles. Your skeletal system and your muscular
system work together and move your body.
Cartilage
Red bone marrow
Spongy bone
Yellow bone marrow
Periosteum
Compact bone
Visual Check
4. Identify Circle the red
bone marrow in the bone
shown in the figure.
Blood vessels
Compact Bone Tissue
Find the compact bone tissue in the figure above. The
hard, outer area of long bones is made up mostly of compact
bone tissue. This tissue is a thick, dense web of fibers.
Spongy Bone Tissue
Spongy bone tissue is located near the ends of long
bones, such as the arm bone in the figure above. A short
bone, such as the one in your wrist, is mostly spongy bone
tissue. The small holes in spongy bone tissue make it look
like a sponge. Because of these holes, spongy bone tissue is
not as dense as compact bone tissue.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Bone Marrow
The inside of most bones is made up of a soft tissue called
bone marrow (MER oh). There are two types of bone marrow.
Red bone marrow is the tissue where red blood cells are
made. It is found in the spongy ends of long bones and in
some flat bones, such as the ribs. Yellow bone marrow stores
fat. Yellow bone marrow is found in the longest part of long
bones.
Reading Check
5. Contrast What is the
difference between red bone
marrow and yellow bone
marrow?
Cartilage
The strong, flexible tissue that covers the ends of bones is called
cartilage (KAR tuh lihj). Cartilage is shown in the figure above.
Cartilage keeps the surfaces of bones from rubbing against
each other. It protects bones and reduces friction in joints.
Periosteum
The parts of a bone that are not covered by cartilage are
covered by periosteum (per ee AHS tee um). The periosteum is
a membrane that surrounds bone. This thin tissue has blood
vessels, nerves, and cells that make new bone tissue. It helps
bones function and grow properly. It also helps a bone heal
after an injury.
Reading Essentials
Make a half-book, then draw
and describe what a bone is
made of.
Periosteum
Compact bone
tissue
Spongy bone
tissue
Cartilage
Bone
marrow
Structure and Movement
227
Formation of Bones
Reading Check
6. Sequence the steps in
bone formation.
Before you were born, your skeleton was made mostly of
cartilage. During infancy and childhood, the cartilage was
slowly replaced by bone. The long bones in your body, such
as the bones in your legs and arms, have areas of growth
that produce new bone cells. These areas are called growth
plates. Growth plates produce cartilage that is then replaced
by bone tissue. A growth plate is the weakest part of an
adolescent bone. Growth continues until adulthood, when
most cartilage has turned to bone.
Joints
Your bones work together to move your body. They work
together at places called joints. A joint is where two or more
bones meet. Joints provide flexibility and enable the skeleton
to move. Ligaments (LIH guh munts) are tissues that connect bones
to other bones. When the bones in joints move, ligaments
stretch and keep the bones in place. Ligaments connect
bones at joints, but they do not protect bones. Cartilage
protects the ends of bones. Your skeletal system has two
types of joints—immovable joints and movable joints.
Immovable Joints
Some parts of your skeleton are made of bones that are
connected but do not move. These are called immovable
joints. Your skull has several immovable joints.
Key Concept Check
7. Explain How do
ligaments and cartilage
help your skeletal system
function?
You are able to move your hands and bend your body
because of movable joints. You can move in many ways
because of your body’s movable joints. The three main types
of movable joints and the ligaments that hold them together
are shown in the table below.
Types of Movable Joints
Joint
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Structure and Movement
Examples
Ball and socket
Bones can move and
rotate in nearly all
directions.
hips and shoulders
Hinge
Bones can move back
and forth in a single
direction.
fingers, elbows, knees
Pivot
Bones can rotate.
neck, lower arm
below the elbow
Visual Check
8. Identify Where in your
body are hinge joints?
Description
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Movable Joints
Bone Injuries and Diseases
Because bones are made of living tissue, they can be
injured. Bones can break. They can also develop disease.
Broken Bones
A broken bone is called a fracture (FRAK chur). Broken
bones can repair themselves, but it takes a long time. A
broken bone must be held together while it heals. Sometimes
a person wears a cast to hold a bone in place while it heals.
Sometimes metal plates and screws hold a bone together
while it heals.
Arthritis
Arthritis (ar THRI tus) is a disease in which joints become irritated
or inflamed, such as when cartilage in joints is damaged or wears away.
When the joints become irritated, it can be painful to move.
Arthritis is most common in adults. It can also affect children.
9. Analyze What are some
ways to help a fractured
bone heal?
Osteoporosis
Another common bone disease is osteoporosis
(ahs tee oh puh ROH sus). Osteoporosis is a disease that causes
bones to weaken and become brittle, or easily broken. Osteoporosis
can change a person’s skeleton and cause fractures.
Osteoporosis is most common in women over the age of 50.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Healthy Bones
One of the best ways to keep bones healthy is to exercise.
Certain types of exercise, such as running, walking, and
lifting weights, place weight on your bones. These types of
exercises help make bones strong and build new bone tissue.
A balanced diet also helps keep bones healthy. Bones
need calcium and vitamin D most of all. Calcium makes
bones strong. It is also important for cell processes. If you do
not have enough calcium in your diet, your body will use
the calcium stored in your bones. This can make your bones
weak. Vitamin D helps the body use calcium.
The Skeletal System and Homeostasis
Homeostasis is an organism’s ability to keep its internal
conditions stable. Homeostasis requires that all body systems
work together properly. Your skeletal system helps your body
maintain homeostasis by supplying calcium to your nerves,
heart, and muscles so they can function properly. Bones also
help you respond to unpleasant stimuli, such as a buzzing
mosquito. Working together with muscles, bones enable you
to move away from or even swat a mosquito.
Reading Essentials
Key Concept Check
10. Explain How does
the skeletal system help the
body maintain homeostasis?
Structure and Movement
229
Mini Glossary
arthritis (ar THRI tus): a disease in which joints become
irritated or inflamed, such as when cartilage in joints is
damaged or wears away
cartilage (KAR tuh lihj): a strong, flexible tissue that covers
the ends of bones
joint: where two or more bones meet
ligament (LIH guh munt): tissue that connects bones to
osteoporosis (ahs tee oh puh ROH sus): a disease that
causes bones to weaken and become brittle
periosteum (per ee AHS tee um): a membrane that
surrounds bone
skeletal (SKE luh tul) system: contains bones as well as
other structures that connect and protect the bones and that
support other functions in the body
other bones
1. Review the terms and their definitions in the Mini Glossary. Write a sentence or two that
describes the relationship between the skeletal system and joints.
2. On the blanks in the diagram below, write the parts of the bone.
Red bone marrow
Blood vessels
Periosteum
3. How did highlighting information about the skeletal system help you understand what
you read?
What do you think
Reread the statements at the beginning of the
lesson. Fill in the After column with an A if you
agree with the statement or a D if you disagree.
Did you change your mind?
230
Structure and Movement
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LESSON
Reading Essentials
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Yellow bone marrow