Structure and Movement The Skeletal System Functions of the Skeletal System

Structure and Movement
The Skeletal System
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.
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.
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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.
Movement
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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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
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.
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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.
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.
Formation of Bones
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.
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
Description
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
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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.
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.
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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.