The Skeletal System
Support
Protection
Movement
Topics covered
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Structure and development
Remodel and repair
How bones fit together to make the
skeleton
How joints enable bones and muscles to
work together
Problems with the skeletal system
Skeletal system consists of 3
types of connective tissue
1.
2.
3.
Bones – the hard elements
Ligaments – dense, fibrous connective
tissue that binds bone to bone
Cartilage – special connective tissue of
fibrous & elastic collagen in a gel-like
fluid called “ground substance”
Long bone
ligaments
Cartilage
Bones: The hard elements
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Most bone mass consists of nonliving
extra cellular crystals of calcium
minerals
Also consists of:
Living bone cells, nerves and blood
vessels (bones bleed when they are cut
or broken!)
5 Bone Functions
1.
2.
3.
4.
5.
Support
Movement
Protection
Formation of blood cells
Mineral storage
1. Support
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Bones form the structure (skeleton) to
which the skeletal muscles are attached
http://kidshealth.org/misc/movie/bodyb
asics/bodybasics_knee.html
2. Movement
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Bones support and interact with
muscles making movement possible
3. Protection
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As hard elements
bones surround and
protect many
delicate internal
organs
4. Blood cell formation
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Certain bones
contain cells that are
responsible for
making different
types of blood cells
5. Mineral Storage
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Calcium, phosphates which are
important to metabolic function
http://www.octc.kctcs.edu/GCaplan/ana
t/Notes/API%20Notes%20H%20Skeleta
l%20System.htm
Long bones
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Longer than wide
Cylindrical shaft called diaphysis
Enlarged knobs at each end called epiphysis
Compact bone forms the shaft and covers
each end
Central cavity of the shaft is filled with yellow
bone marrow (primarily fat for energy)
Epiphysis
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Inside each epihysis is spongy bone
that is less dense than compact bone
making it light, but strong
Spongy bone is a lattice work of hard
relatively strong trabeculae (L. little
beams) made of calcium, minerals and
living cells
Long bone special function
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Upper arms and legs (humerous and
femur) contain spaces between the
trabeculae that are filled with red bone
marrow.
Stem cells in the red marrow are
responsible for the production of red
and white blood cells and platelets
Outer surface - periosteum
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Bones are covered by tissue called
periosteum that contains specialized
bone forming cells: osteocytes (Gk.
Bone & cells)
Osteocytes are arranged in rings in
cylindrical structures called osteons
(sometimes called Haversian systems)
Periosteum cont’d
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As bone develops and hardens
osteocytes become trapped in
chambers called lacunae – but stay in
touch with each other via canals called
canaliculi.
Canaliculi are used to pass nutrients
between adjacent osteocytes to nurture
bone cells when far from blood vessels
Osteocytes in lacunae
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Waste products
diffuse in the
opposite direction
and are removed by
the blood vessels for
transport to urinary
system
Osteocytes in trabeculae
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In spongy bone osteocytes don’t need
canals for nutrients and waste
transportation – the trabeculae
structure gives the osteocytes access to
nearby blood vessels in the red marrow
http://cellbio.utmb.edu/microanatomy/b
one/compact_bone_histology.htm
Ligaments hold bones
together
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Attach bone to bone
Packed collagen fibers all oriented in
the same direction
Confer strength to certain joints while
permitting movement of bones in
relation to each other
Cartilage lends support
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Fibers of collagen and elastin in a
ground substance of mostly water
Smoother and more flexible than bone
Found where support under pressure is
needed and where some movement is
necessary
3 types of cartilage
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Fibrocartilage – found in areas requiring
ability to withstand high pressure &
tension (intervertebral discs, menisci of
knees)
Hyaline cartilage – forms the embryonic
structures that become bones; covers
the end of mature bones in joints
Elastic cartilage – highly flexible (ears,
epiglottis
Development of bone
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Chondroblasts – cartilage forming cells
of earliest stages of fetal development
At 2-3 months in utero the cartilage
models begin to dissolve and are
replaced by bone = ossification
When chondroblasts die the matrix they
produced breaks down making room for
blood vessels
Development continued
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The blood vessels carry osteoblasts (Gk
bone + to form) into the area where
the matrix was from the periosteum.
Osteoblasts secrete osteoid (a mixture
of proteins and collagen) that becomes
the strong internal structure of the bone
Osteoblasts also secrete enzymes that
help form hydroxyapatite (crystals of
hard mineral salts around the osteoid
matrix)
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Eventually mature osteocytes become
embedded in hardened lacunae where
they maintain the bone matrix
Bones continue to lengthen throughout
childhood and adolescence because of
the growth plate (epiphyseal plate) in
each epiphysis
As bone lengthens the plates at each
end grow farther apart
Bones also grow in width as osteoblasts
lay down bone just below periosteum
Bone development controlled
by hormones
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Growth hormone during preadolesence
Sex hormones during puberty stimulate
growth plates at first
By 18 in women and 21 in men the
same sex hormones signal the growth
plates to stop growing
Growth plates close but bones can still
grow wider
Remodeling and repair
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Bone is either forming or disintegrating
as long as you live
Osteoclast (Gk: bone + to break) is
another type of bone cell that cuts
through mature bone tissue and
dissolves the hydroxyapatite and
digests the osteoid matrix
Released calcium and phosphate ions
enter the blood
Bone remodel & repair
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Where bone has been removed
osteoblasts are attracted to lay down
new osteoid matrixes and stimulate
new deposits of hydroxyapatite crystals
Bones change size, shape &
strength
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Compression causes tiny electrical
currents (jogging) within the bone that
stimulate bone-forming activity of the
osteoblasts
So new bone is laid down in areas
under high compressive stress and
bone is reabsorbed in areas of low
stress
Weight-bearing exercise
increases bone mass!
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Jogging, weight lifting causes your
bones to become stronger & more
dense
Homeostasis of bone structure depends
on a balance of the activities of the
osteoblasts and osteoclasts
Osteoporosis – great loss of bone mass
due to imbalance of the activities of the
2 types of bone cells
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Your body will take minerals from your
bones if blood levels are low
PTH will stimulate osteoclasts to
dissolve bone
About 10% of bone is remodeled or
replaced each year in young adults
Repair - fractures
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First a blood clot or hematoma forms at
the break site as the bone bleeds
Inflammation, swelling and pain
immobilize the area
Repair begins within days as fibroblasts
migrate to the area
Some become chondroblasts and
together with fibroblasts make a callus
Repair
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The callus appears between the broken
ends of the bone
Osteoclasts arrive and clear fragments
of original bone as well as the blood
cells of the hematoma
Finally osteoblasts arrive to lay down
new matrix and start hydroxyapatite
formation & callus becomes bone
Repair
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Bones rarely break in the same place
twice because the repaired area is
thicker than the original bone
The repair process slows with age and
applications of weak electrical current
can increase the rate of healing –
perhaps by attracting osteoblasts
The skeleton protects, supports
and permits movement
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Classification of 206 bones:
Long bones – limbs, finger
Short bones - wrists
Flat bones – cranium, sternum, ribs
Irregular bones – coxal (hip), vertebrae
3 functions of skeleton
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Support of soft organs
Protection from injury (skull)
Permits flexible movement (joints0
Skeletal organization
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Axial skeleton – skull, vertebral column,
ribs, sternum
Appendicular skeleton – pectoral girdle,
pelvic girdle, limbs
Axial – Skull bones
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Cranial – flat bones enclose and protect
brain
Frontal bone: forehead and upper
ridges of eye sockets
Parietal bones: upper left and right
sides of skull
Temporal bones: lower left and right
(ears)
Skull bones cont’d
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Sphenoid bone: back of the eye
sockets
Ethmoid bone: contributes to eye
sockets and helps to support the nose
Occipital bone: curves underneath to
form the back & base of the skull
Foramen magnum (L. great opening):
where vertebrae connects to skull
But wait, there’s more
Skull bones!
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Facial bones - front
Maxilla – forms part of eye sockets and
sockets to anchor upper row of teeth
Palatine bones – hard palate (roof of
mouth)
Vomer bone – behind palatine & part of
nasal septum
But wait, there’s more
Skull bones!
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Zygomatic bones: cheek bones & outer
portion of eye socket
Nasal bones: underlie the upper bridge
of nose (space between maxilla & nasal
bones is the nasal cavity)
Lacrimal bones: inner eye sockets with
tear duct (drains to nasal cavity)
All skull bones joined tightly except
for mandible (speak & chew)
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Mandible: lower jaw w/ sockets for
teeth
Sinuses are air spaces which make the
skull lighter and give the human voice
its tone and resonance
Each sinus is lined with tissue that
secretes mucus & connects to nasal
cavity by small passageways
Blocked sinuses = pain
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Respiratory infections cause sinus tissue
to become inflamed and block the
passages to the nasal cavity
Sinusitis = sinus inflammation
Fluid gets trapped causing sinus
pressure headache