The Skeletal System
• Organ system that supports and protects the body
and allows it to move
• Support – bones provide support for your body and
make it possible to sit or stand upright
• Protection – bones provide protection to organs –
for example: ribs protect the heart and lungs
• Storage – outer layer of bone – compact bone –
stores minerals like calcium
• Blood cell production – in the center of flat bones is
soft tissue called marrow - red marrow makes
blood cells
• Movement – bones provide a place for muscles to
attach – muscles pull on bones to make movement
Parts of the Skeletal System
• Bones, ligaments and cartilage make up your
skeletal system
• Skeletal system is divided into two parts –
axial skeleton – skull, vertebrae and ribs
appendicular skeleton - arms, legs,
shoulders and pelvis
• Bones – have blood vessels to supply
nutrients and nerves to feel pain
• Newborn babies have about 300 bones - the
average adult has 206 bones
• Ligaments – tough, flexible strands of connective
tissue that hold bones together
• Some allow for movement and are found at the end
of the bone
• Some ligaments prevent too much movement
• Cartilage – a strong, flexible and smooth connective
tissue found at the end of bones – it allows bones
to move smoothly across each other
• The tip of your nose and your ears contain only
cartilage
• Cartilage does not contain blood vessels
What are Bones Made Of?
• Bones are hard organs made of minerals and
connective tissue
• Compact bone – a kind of bone tissue that is dense
and has no visible open spaces – makes bones rigid
and hard
• Spongy bone – a kind of bone tissue has many open
spaces – provides most of the strength and support
for the bone
• Calcium is the most plentiful mineral in bones –
minerals are deposited by bone cells called
osteoblasts
• Connective tissue in bones is made mostly of
collagen
• Collagen allows bones to be flexible enough to
withstand knocks and bumps
• Marrow – soft tissue inside bones
• Two types of marrow:
red marrow is where red and white blood cells are
produced – found in flat bones like the ribs
yellow marrow is found in the center of long bones
like the femur and stores fat
How Do Bones Grow?
• The skeleton of a fetus growing inside its mother’s
body does not contain hard bones
• Most bones start out as cartilage
• As a baby grows, most of the cartilage is replaced
by bone
• Long bones lengthen at their ends in areas called
growth plates – areas of cartilage that make new
cells
• Bone cells called osteocytes move into the
cartilage, hardening it and changing it into bone
• Growth continues into adolescence and sometimes
early adulthood
How Are Bones Connected?
• The place where two or more bones connect is called a
joint
• Some joints allow for movement – moveable joints
and others stop or limit movement – fixed joints (found
in the skull)
• Bones are connected to each other at joints by
ligaments
• Cartilage helps cushion the area in a joint where bones
meet
• Ball and socket joint – shoulders and hips – allows one
bone to rotate in a large circle
• Gliding joint – allow flexibility in a lot of direction –
wrists and ankles
• Hinge joint – allows bones to move back and forth –
knees and elbows
What are Some Injuries or Disorders of
the Skeletal System?
• Fractures – broken bone – usually repairs itself in 6
to 8 weeks – can mend itself but doctors help by
putting the ends together
• Sprains – an injury to a ligament caused by
stretching a joint too far – ligament tissue can tear
and the joint becomes swollen
• Osteoporosis – disease that causes bone tissue to
become thin – bones become weak and break
easily
• Arthritis – disease that causes joints to swell,
stiffen and become painful – makes joint
movement difficult