The Skeletal System
Bones, Skeleton, & Joints
Unit Objectives
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Identify the subdivisions of the skeleton as axial or appendicular
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Axial
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Appendicular
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On a skull or diagram, identify & name the bones of the skull
Describe how the skull of a newborn infant differs from that of an adult, and explain the function of fontanels
Name the various parts of a typical vertebra
Discuss the importance of the intervertebral discs and spinal curvatures
Explain how the abnormal spinal curvatures (scoliosis, lordosis, and kyphosis) differ from one another
Identify on a skeleton or diagram the bones of the shoulder and pelvic girdles and their attached limbs
Describe important differences between a male and female pelvis
List at least 3 functions of the skeletal system
Name the four main kinds of bones
Identify the major anatomical areas of a long bone
Explain the role of bone salts and the organic matrix in making bone both hard & flexible
Describe briefly the process of bone formation in the fetus and summarize the events of bone
remodeling
Name & Describe the various types of fractures
Name the 3 major categories of joints and compare the amount of movement allowed by each
Understand the functions and differences between tendons & ligaments
Identify some of the causes of bone and joint problems throughout life
Functions of Bone
Support & Give shape to the body
 Protects Internal Organs
 Helps make movements possible
 Stores calcium
 Hemopoiesis or blood cell formation
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Types of Bones
Long
 Short
 Flat
 Irregular
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Structure of Long Bones
Diaphysis or shaft
 Medullary cavity containing yellow marrow
 Epiphyses or ends of the bone; spongy bone
contains red bone marrow
 Articular cartilage-covers epiphyses as a
cushion
 Periosteum-strong membrane covering bone
except at joint surfaces
 Endostuem-lines the medullary cavity
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Microscopic Structure of
Bone and Cartilage
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Bone types
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Spongy
 Texture
results from needlelike threads of bone called
trabeculae surrounded by a network of open spaces
 Found in epiphyses of bones
 Spaces contain red bone marrow
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Compact
 Structural
unit is Haversian system-composed of
concentric lamella, lacunae containing osteocytes,
and canaliculi, all covered by periosteum
Osteocyte in lacuna
Lamella
Haversian System
Microscopic Structure of
Bone and Cartilage con’t
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Cartilage
Cell type called chondrocyte
 Matrix is gel-like and lacks blood vessels
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Bone formation & Growth
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Sequence of development early-cartilage
models replaced by calcified bone matirx
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The laying down of calcium salts in the gel-like
matrix of the forming bones is an ongoing
process
Osteoblasts form new bone, osteoclasts
reabsorb bone
Development of Bone from
Fetus
An infant’s skeleton has many bones that
are not yet completely ossified “formed in
cartilage”
 Fontanels: soft spots on an infant’s skull
 Long bone grows from small centers at both
ends called epiphyses
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As long as cartilage remains in epiphyseal plate
body will grow
Division of Skeleton
The skeleton is composed of the following
divisions & subdivisions
 Axial Skeleton
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Skull
Spine
Thorax
Hyoid bone
Appendicular Skeleton
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Upper Extremities, including shoulder girdle
Lower Extremities, including hip girdle
Differences between a Man’s
& a Woman’s skeleton
Size: Male skeleton is generally larger
 Shape of pelvis: male pelvis is deep and
narrow, female pelvis is broad and shallow
 Size of pelvic inlet: female pelvis inlet is
generally wider, normally large enough for
baby’s head to pass through it
 Pubic angle: angle between pubic bones of
female generally wider
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Joint (Articulations)
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Kinds of joints
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Synarthroses (no movement)-fibrous connective tissue
grows between articulating bones, for example, sutures
of skull
Amphiarthroses (slight movement)-cartilage connects
articulating bones; for example symphysis pubis
Diarthroses (free movement)-most joints belong
to this class
 Structures
of freely movable joints-joint capsule and
ligaments hold adjoining bones together but permit
movement at joint
Joints con’t
Articular cartilage-covers joint ends of bones
and absorbs joints
 Synovial membrane-lines joint capsule and
secretes lubricating fluid
 Joint cavity-space between joint ends of
bones
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Types of freely movable
joints
Ball-and-Socket
 Hinge
 Pivot
 Saddle
 Gliding
 Condyloid
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Bone Remodeling & Repair
Remodeling: balance of bone deposit &
removal, deposits occur at a greater rate
when bone is injured
 Controlled by
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Hormone used to maintain blood calcium
 In response to mechanical stress and gravity,
remodels so it is able to withstand the stresses
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Bone Remodeling & Repair
con’t
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Repair
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Fractures are breaks in bones & are classified
by:
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Comminuted: bone fragments into 3 or more pieces (common with more
brittle bones)
Compression: bone is crushed (common with more brittle bones)
Spiral: Ragged break occurs when excessive twisting force is applied to
bone (common sports fracture)
Epiphyseal: epiphysis separates from the diaphysis along the
epiphyseal plate (common where cartilage is dying)
Depressed: Broken bone portion is pressed inward (common of skull)
Greenstick: bone breaks incompletely (common in children whose
bones are more flexible)
Bone Remodeling & Repair
con’t
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Repair 4 stages
Hematoma formation
 Fibrocartilaginous callus formation
 Bony callus formation
 Remodeling of the bony callus
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Bone & Joint Problems
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Bone Problems
Osteomalacia: number of disorders in adults in
which the bone is inadequately mineralized
 Rickets: inadequate mineralization of bones in
children caused by insufficient calcium or
vitamin D deficiency
 Osteoporosis: group of disorders in which the
rate of bone reabsorption exceeds the rate of
formation
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Bone & Joint Problems
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Joint Problems
Sprains
 Dislocations
 Bursitis: inflammation of bursa, caused by a
blow or friction
 Tendonitis: inflammation of the tendons, caused
by overuse
 Arthritis: inflammatory or degenerative diseases
that damage the joints, resulting in pain,
stiffness, and swelling of joint
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Spinal Curvatures
5 major divisions; cervical (7), thoracic (12),
lumbar (5), fused of sacrum (5), fused of
coccyx (4)
 Increase resiliency & flexibility
 Cervical & lumbar curvatures are concave
posteriorly, and the thoracic & sacral
curvatures are convex posteriorly
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Intervertebral disc
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Cushion like pads that act as shock
absorbers and allow the spine to flex,
extend, and bend laterally
Abnormal Spinal
Curvatures
Scoliosis: spine is curved from side to side
 Lordosis: spine lumbar region is curved
inward
 Kyphosis: curving of the spine causes a
bowing of the back
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