Skeletal System
The Skeletal System: Overview
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Components of the skeletal system
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Bones (~ 206 in an adult)
Joints
Cartilages
Ligaments
Two divisions
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Axial skeleton
Appendicular skeleton
Primary Functions of the Skeletal
System
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1. Structural support – framework for the
attachment of soft tissues and organs
2. Protection of soft organs
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Ribs – protect the heart and lungs
Skull – protects the brain
Vertebrae – shield the spinal cord
Pelvis – protects digestive & reproductive
organs
Primary Functions of the Skeletal
System
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3. Storage – calcium salts (Mineral reserve)
& lipids (energy reserve in the yellow
marrow)
Yellow bone marrow
Primary Functions of the Skeletal
System
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4. Red Blood cell formation – red marrow
Primary Functions of the Skeletal
System
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5. Leverage for body movements –
delicate to powerful motions
Bone Composition
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Two types of bone tissue:
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Compact bone: Homogeneous, relatively
solid & protective outer layer
Spongy bone: Open network of small
needle-like pieces of bone
Figure 5.2b
Bones – Composition
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Mass of a bone attributed to
three components
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2/3 calcium deposits
1/3 collagen fibers
Osteocytes & other cells ~ 2%
Classification of Bones on the Basis
of Shape
Figure 5.1
Classification of Bones
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1. Long bones
 Have a shaft with heads at both ends
 Contain mostly compact bone
 Examples: Femur, humerus, metacarpals
Classification of Bones
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2. Short bones
 Generally cube-shape
 Contain mostly spongy bone
 Examples: Carpals, tarsals
Classification of Bones
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3. Flat bones
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Thin & often curved
Thin layers of compact bone around a layer
of spongy bone
 Examples: Skull, ribs, sternum
Classification of Bones
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4. Irregular bones
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Odd shapes
Do not fit into other categories
Example: Vertebrae and pelvis
Gross Anatomy of A Long Bone
Gross Anatomy of a Long Bone
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Diaphysis
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Shaft
Composed of compact bone
Figure 5.2a
Gross Anatomy of a Long Bone
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Epiphysis
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Ends of the bone
Composed mostly of spongy bone
Covered by articular cartilage
Articulates with another bone at a joint
Figure 5.2a
Structures of a Long Bone
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Periosteum
 Outside covering of the diaphysis –
isolates bone from surrounding tissues
 Fibrous connective tissue membrane –
provides passage for blood vessels &
nerves
Figure 5.2c
Structures of a Long Bone
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Sharpey’s fibers - Secure periosteum to
underlying bone
Structures of a Long Bone
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Articular cartilage
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Covers the external surface of the epiphyses
Hyaline cartilage
Decreases friction at joint surfaces
Structures of a Long Bone
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Medullary cavity
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Cavity of the shaft – lined by the endosteum
Contains yellow marrow (mostly fat) in adults
Contains red marrow (for blood cell formation)
in infants
Figure 5.2a
Bone Markings
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Surface features of bones
Sites of attachments for muscles,
tendons, and ligaments
Passages for nerves and blood vessels
***You are responsible for the bone
markings on your notes page***
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What they are and their function
Joints
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Articulations of bones – exist wherever
two bones meet
Functions of joints: strength & mobility
Structural Classification of Joints
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Fibrous joints - Generally immovable
Cartilaginous joints - Immovable or slightly
moveable
Synovial joints - Freely moveable
Functional Classification of Joints
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Synarthroses – immovable joints
Amphiarthroses – slightly moveable joints
Diarthroses – freely moveable joints
Synarthroses
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Bony edges are close together and may
interlock
Suture – bones interlocked and bound together
with dense connective tissue (skull)
Syndesmoses (fibrous)
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Allows more movement than sutures due to
longer connective fibers
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The joints have more “give”
Distal ends of the tibia and fibula
Amphiarthroses
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Symphysis (cartilaginous): Bones connected
by cartilage
Examples
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Pubic symphysis
Intervertebral joints
Figure 5.27d–e
Diarthroses (Synovial Joints)
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Articulating
bones are
separated by a
joint cavity
Typically found
at the ends of
long bones
Synovial fluid is
found in the joint
cavity
Figure 5.24f–h
Features of Synovial Joints
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Joint surfaces are enclosed by a fibrous
articular capsule
Ligaments reinforce the joint
Features of Synovial Joints
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Bursae – small packets of connective tissue
filled with synovial fluid
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Shock absorber/ friction reducer
Found where tendons or ligaments rub against
other tissues
Features of Complex Synovial Joints
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Meniscus - shock absorbing fibrocartilage pad
Fat pads – protect the articular cartilages & act as
“filler”
Types of Synovial Joints Based on
Shape
Figure 5.29a–c
Plane/Gliding Joint
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Articular surfaces are flat
Short slipping or gliding
movements
Nonaxial - no rotation
Carpal and tarsal joints
Ends of clavicles
Hinge Joint
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Cylindrical end of one bone fits into a
trough-shaped surface on the other
Uniaxial – movement around one axis
Elbow & joints of the phalanges
Pivot Joint
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Uniaxial joints – rounded end of one bone
fits into a sleeve or ring of bone
Proximal radioulnar joint
The atlas and dens of the axis
Condyloid (ellipsoidal) Joint
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Biaxial – can rotate around two different axes
Oval shaped articular surface & concavity
Bone may travel from side to side & back and
forth
Metacarpophalangeal joints
Saddle Joints
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Biaxial Joint – articulated surfaces have
convex and concave surfaces
Joint of the thumb
Ball-and-Socket Joint
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Only multiaxial joints – spherical head of
one bone fits into the round socket of
another
Provide greatest variation in motion
Inflammatory Conditions Associated
with Joints
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Bursitis – inflammation of a bursa usually
caused by a blow or friction
Tendonitis – inflammation of tendon
sheaths
Rheumatism
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General term describing pain or stiffness
arising in the muscular or skeletal system
Several major forms of rheumatism:
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Arthritis – inflammatory or degenerative diseases
of joints
Also known as degenerative joint disease (DJD)
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25% of women and 15 % of men over age 60 show signs of
this disorder
Over 100 different types
The most widespread crippling disease in the United States
Clinical Forms of Arthritis
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Osteoarthritis: Most common chronic arthritis
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Probably related to normal aging processes –
softening, fraying and breakdown of the articular
cartilage
Exposed bone thickens into spurs – limits
movement
Clinical Forms of Arthritis
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Rheumatoid arthritis
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An autoimmune disease – the immune system
attacks the joints
Often leads to deformities in hands and feet
Clinical Forms of Arthritis
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Gouty Arthritis: Inflammation of joints is
caused by a deposition of urate crystals from
the blood
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Needle like crystals usually accumulate in one joint
– typically the big toe
Can usually be controlled with diet
Review- Correctly label the types of joints
Review – Correctly label the four types of
bones and give an example of each
Figure 5.1
Review – Label the main structures of
a long bone
Microscopic Anatomy of Bone
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Osteon (Haversian System)
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A unit of bone
Microscopic Anatomy of Bone
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Central (Haversian) canal
 Opening in the center of an osteon
 Carries blood vessels and nerves
Microscopic Anatomy of Bone
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Perforating (Volkman’s) canal
 Canal perpendicular to the central canal
 Carries blood vessels and nerves
Microscopic Anatomy of Bone
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Lacunae: Cavities containing bone cells
(osteocytes)
 Arranged in concentric rings
Detail of Figure 5.3
Microscopic Anatomy of Bone
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Lamellae: Rings around the central canal
 Sites of lacunae
Microscopic Anatomy of Bone
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Canaliculi: Tiny canals that form a transport
system between individual cells
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Radiate from the central canal to lacunae
Detail of Figure 5.3
Types of Bone Cells
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Osteocytes - Mature bone cells
Maintain normal bone structure
 Recycle calcium salts
 Assist in bone repair
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Types of Bone Cells
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Osteoblasts: Responsible for osteogenesis
(bone formation)
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Produce new bone matrix
Promote the deposition of calcium salts in the bone
matrix
When completely surrounded by calcified matrix it
will differentiate into an osteocyte
Types of Bone Cells
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Osteoclasts - Bone-destroying cells
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Produce large amounts of acids and enzymes
Osteolysis – as bony matrix dissolves, stored
minerals are released
Helps regulate calcium and phosphate levels
Ossification & Bone Growth
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Skeletal growth begins
about 6 weeks after
fertilization
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All skeletal components
are initially composed of
cartilage
Bone growth continues
through adolescence
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Some portions continue
to grow until about age 25
Ossification
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Process of replacing other tissues with bone
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Intramembranous – bone develops within sheets
or membranes of connective tissue
Endochondral – bone replaces existing hyaline
cartilage
 Most bones are formed in this way
Long Bone Formation and Growth
Figure 5.4b
Bone Growth and Remodeling
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Bones are remodeled and lengthened until growth
stops
Appositional growth – as the bones lengthen they
also increase in diameter
 Cells of the periosteum develop into osteoblasts
and produce bone matrix
 Inner surface eroded by osteoclasts increasing
the diameter of the marrow cavity
Bone Growth and Remodeling
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Reliable source of minerals needed for growth
to occur – absorbed from mother while
developing
 Mother often loses bone mass during
pregnancy
 Diet must have adequate amounts of calcium,
phosphates & Vitamin D3
Bone Remodeling
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Normal process of protein and mineral
composition being removed and replaced
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About 18% each year in adults
Causes bones to change shape
May change shape/size in response to stresses such
as fractures, breaks or change in muscle mass
Bone mass lost with disuse and age
Bone Health
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Bones become stronger in response to stress
When we are inactive (no exercise) – bones
become weak and fragile
Areas That Do Not Undergo
Ossification
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Cartilage remains in isolated areas
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Bridge of the nose
Larynx
Trachea
Parts of ribs
Joints
Skeletal Disorders
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Heterotopic Bones: abnormal development of
osteoblasts in normal connective tissues
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Fibrodysplasia Ossificans Progressiva: rare genetic
heterotopic disorder
Muscles of the back, neck & upper limbs gradually
replaced by bone
Rickets
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Softening and bending of the bones due to
Vitamin D3 deficiency
 Children get bowed legs as they bend under
the weight of the body
 No longer common (in US) due to dietary
supplements
Scurvy
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Vitamin C deficiency causes reduction in
osteoblast activity
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Weak and brittle bones
Common on ships
Osteopenia
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Bones become thinner and
weaker with age
Reduction in bone mass begins
between ages 30 – 40
Important to build strong bones as
a child/ young adult
Osteopenia
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Osteoblast activity declines
Osteoclast activity remains normal
Women lose about 8% and men about 3% of their
bone mass every decade
Epiphyses, vertebrae & jaws affected the most
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Fragile joints/limbs, height reduction and tooth loss
Osteoporosis
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Bone-thinning disease that afflicts half of
women over 65 and 20% of men over 70
Bones are brittle and fracture easily
Often causes kyphosis due to vertebral
collapse
Caused partially by estrogen deficiency after
menopause
Other factors include lack of calcium, protein
and vitamin D in the diet, smoking and
insufficient weight-bearing exercise
Osteoporosis
Bone Fractures
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A break in a bone
Types of bone fractures
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Closed (simple) fracture – break that does not
penetrate the skin
Open (compound) fracture – broken bone penetrates
through the skin
Treating Bone Fractures
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Bone fractures are treated by reduction and
immobilization
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Realignment of broken bone ends
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Closed reduction - bone ends coaxed back into place
by physician's hands
Open reduction - surgery, bone ends secured together
with pins, wires or plates & screws
Types of Bone Fractures
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Comminuted - bone fragments into many pieces
Compression - bone is crushed ( due to porous
bone)
Depressed - broken bone is pressed inward (e.g. in
skull)
Transverse - break occurs across the long axis of a
bone
Types of Bone Fractures
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Impacted - broken bone ends are forced into each
other
Spiral - ragged break as a result of excessive
twisting of bone
Epiphyseal - break occurring along epiphyseal
line/plate
Greenstick - bone breaks incompletely
Common Types of Fractures
Table 5.2
Bone Remodeling After a Fracture
Review – label the microscopic anatomy
of the bone