13 – 3 What is the skeletal system?
Key Terms
Skeletal system: system of bones and
cartilage that helps to support and protect the
body.
vertebrae: bones that make up the
backbone
cartilage: tough, flexible connective tissue
The Skeletal System Have you ever seen a
house being built? If you have, you have
probably seen the wooden framework that
makes up a house. The framework of a
house is important. It gives a house its
shape. The framework also supports a
house. You also have a frame that supports
your body. This frame is your skeleton. Most
of your skeletal system is made of bone.
Bone is a very hard tissue.
Kinds of Skeletons Some living things do
not have a skeleton. Their bodies are entirely
soft. Other organisms, such as lobsters and
insects, have an exoskeleton, or s skeleton
outside their bodies. An exoskeleton is tough
and hard. It protects the animal. Humans and
many other animals have an endoskeleton,
or a skeleton inside their bodies.
Jobs of the Skeleton A major job of the
skeletal system is to support the body. The
spine, or backbone, supports the body and
also allows for a variety of movements. The
backbone is made up of separate bones
called vertebrae. These bones resemble a
stack of hollow rings. Because they are
separate bones, the backbone can bend and
twist.
Besides giving support and shape to
your body, your skeletal system has many
other important jobs. One of these jobs is to
work together with muscles to move the
body. Another job of the skeleton is to protect
important organs. For example, the skull
protects the brain. The backbone protects
the spinal cor. Blood cells are made inside
some bones. Bones also store minerals,
such as calcium, that are required by the
body. When they body needs these minerals,
the bone releases them into the blood so
they can be used.
Cartilage
Feel your knee. The bones of
your knee are very hard. Some parts of your
skeleton are not as hard. Move the tip of your
nose. Bend one of your ears with your hand.
These two parts of your body are not made
of bone. They are made of cartilage.
Cartilage is tough, but flexible, connective
tissue. Before you were born, your skeleton
was made of cartilage. However, during the
second and third months of embryonic
development, bone slowly replaced most of
the cartilage in your skeleton.
Bone Formation Over time, the cartilage in
most bones in replaced by hard, living bone
tissue. This process is carried out by several
specialized cells. One type of cell produces
the calcium-enriched material that makes up
most bones. Another cell breaks down bone
tissue during the growth and remodeling of
bones. It may seem strange to have a cell
that destroys bone tissue. However, this
process is very important because the size
and shape of bones change as a person
matures.
CHECKING CONCEPTS
1. A very hard tissue that makes up the skeletal system is __________ tissue.
2. An internal skeleton is called an _______________.
3. The backbone is made up of _______________.
4. The skeletal system works with ___________ to move the body.
5. Before a baby is born,
____________________.
most
of
its
skeleton
is
made
up
of