Download Bones

Skeletal System
Anatomy & Physiology
The Skeletal System
Your skeleton comprises ~ 20% of your
total body mass
 There are 206 bones in your body,
separated into 2 divisions:

– 1. Axial skeleton: head, vertebrae and rib
cage
– 2. Appendicular Skeleton: pelvis,
scapulae and limbs
Axial: pink
Appendicular: green
5 Functions of Bones
1.
2.
3.
4.
5.
Support: legs support the weight of body,
ribs support thoracic cavity
Protections: protects all soft tissue organs
Movement: muscles use bones as levers,
allowing for movement
Storage: fat stored in internal cavities of
bones; calcium and phosphorus also stored
Blood Cell Formation: hematopoesis; the
production of blood cells within marrow
cavities
Bone Types

There are two types of bones:
– 1. Compact bone: dense bone which is
smooth and solid; surrounds all bone;
appears dense
– 2. Spongy bone: internal portion of bone;
consists of small needle-like projections of
bone called trabeculae with many open
spaces filled with marrow
Bone Types
Bone Classification

Bones come in many shapes and sizes and
are classified into 4 distinct groups:
1. Long Bones
o
o
o
o
o
Longer than wide
Built to absorb stress
Consists of a shaft and 2 heads at each end
Mostly compact but some spongy bone internally
Examples: all bones of limbs except patella, carpals
and tarsals
Long Bone: the femur
Bone Classification
2. Short Bones
o Roughly cube-like
o Contains mostly spongy bone
o Thin layer of compact bone on surface
o Examples: carpals and tarsals
o Sesamoid bone: a bone embedded in a
tendon; varies in size and numbers/each
individual; act to alter the pull of a tendon; i.e.
patella
Short Bones: carpals of the wrist
Bone Classification
3. Flat Bones
o Thin, flattened and usually curved
o 2 parallel compact surfaces with a spongy
layer between
o examples: sternum, ribs and skull bones
Bone Classification
4. Irregular Bones
o Do not fit any other classification
o Complicated shapes
o Mostly spongy with thin compact layer
o Examples: vertebrae and hip bones
Anatomical Structure of a Long
Bone
Diaphysis: shaft of long bone; walls
made of compact bone
 Periosteum: fibrous sheath that covers
long bones

– Highly vascularized
– Functions in bone nourishment and
attachment sites
Anatomical Structure of a Long
Bone
Sharpey’s Fibers: connective tissue
fibers that secures the periosteum to
underlying bone
 Epiphyses: ends of long bones

– Enlarged for muscle attachment
– Predominately spongy bone
Anatomical Structure of a Long
Bone

Articular Cartilage: covers ends of
epiphyses and provides a slippery surface
that decrease friction at joint surfaces
 Medullary Cavity: holds marrow in center of
diaphysis
– Yellow marrow: fat storage in adults, found in
medullary cavity
– Red marrow: found in diaphysis of infants, in flat
bones & epiphyses of adults; makes red blood
cells
Anatomical Structure of a Long
Bone

Endosteum:
sheath covering
medullary cavity
Bone Composition

Bone contains inorganic & organic
components
– Inorganic calcium carbonate & calcium
phosphate; provides hardness
– Organic collagen: to further reinforce the
matrix
Osteoporosis: brittle bones
Normal Spongy Bone
Osteoporotic Spongy Bone
Bone Cells: 3 Types
Osteoblasts: arise from embryonic
cells and found on outer surfaces of
adult bones; aid in matrix production
 Osteocytes: mature bone cells;
trapped in lacunae
 Osteoclasts: secretes substances that
dissolve mineral salt crystals

Bone – cell types
Note locations of
Osteoclasts & osteoblasts
“Ruffled” Border
Microscopic Anatomy of Bone

Lacunae: cavities
in bones where
osteocytes are
found
 Lamellae: a
circular layer of
bone
Microscopic Anatomy of Bone
Haversion Canals: a system of
interconnecting canals in adults
compact one; runs lengthwise through
bone, carrying blood vessels and
nerves to all areas of bones
 Canaliculi: tiny canals that connect all
the bone cells to the nutrient supply;
radiate outward from Haversion Canals

Microscopic Anatomy of Bone
Volkmann’s Canals: communication
system from exterior of bone to interior;
runs at right angle to diaphysis
 Osteon/Haversion Systems: each
haversian canal with lamellae,
osteocytes and caniliculi

Haversion Systems
Bone Development
Embryonic Skeleton: predominately
hyaline cartilage
 Fontanels: in skull at birth

– Allows for growth of brain
Bone Development

Young child to late adolescence:
cartilage replaced by bone
– Epiphyseal Growth Plates: allows for
interstitial growth (lengthwise)
– Cartilage near the epiphyses regenerates
– Cartilage near the diaphysis hardens to
bone eventually they’ll meet, halting
lengthwise growth
Epiphyseal Growth Plate
Epiphyseal Growth Plates
Bone Development & Growth
Ossification
The replacement of cartilage by bone
 Cartilage is covered by osteoblasts
 Cartilage is “eaten” away, leaving the
medullary cavity open within the bone

Appositional Growth

Outward growth of bone during adulthood
– Bones change based on calcium levels & muscles
acting on the skeleton
– Decreased blood calcium leads to bone
breakdown
– Increased demand by muscles on bones causes
bone to thicken
– Weight gain also increase bone diameter
– Adult bone constantly remodels (breakdown &
growth) to help maintain homeostasis of blood
mineral levels
Skeletal System
Axial Skeleton
Axial Skeleton
Includes 80 bones of the skull, vertebral
column and bony thorax
 Functions:

– Supports head, neck & trunk
– Protects brain, spinal cord and thoracic
organs
Skull
Composed of flat bones
 Function:

– Used for attachment of head muscles &
protects the brain
Sutures of the Skull

Sutures: interlocking joints that unite
skull bones
– Coronal: where parietal bones meet frontal
– Sagittal: where 2parietal bones meet
superiorly
– Squamos: where parietal and temporal
bones meet on lateral aspects of skull
– Lambdoidal: where parietal bones meet
occipital bones meet posteriorly
Vertebral Column aka the Spine
Location: runs from the base of the
skull to the coccyx (tailbone)
 Function:

– Surrounds and protects the spinal cord
– Provides attachment sites for ribs and back
muscles
Vertebral Column

Characteristics
– 26 interconnected
irregular bones
– Provides a flexible,
curved structure
– Serves as axial
support of the trunk
Vertebral Column

Curvatures of the Spine:
–
–
–
–

S-shaped to prevent shock to head in motion
Allows for trunk flexibility
Increases resiliency & flexibility of the spine
Functions like a spring, not a rod
Cervical & Lumbar Curves: concave
posteriorly
 Thoracic & Sacral Curves: convex
posteriorly
Curvatures of the Spine
Abnormal Curvatures of the
Vertebral Column

Lordosis: aka
sway back
– An accentuated
lumbar curve

Kyphosis: aka
hunchback
– An exaggerated
thoracic curve

Scoliosis: the
twisted disease
– An abnormal lateral
curvature in the
thoracic region
– Typical in girls in late
childhood
Lordosis & Kyphosis
Scoliosis
Cervical Vertebrae

7 total extending from base of skull to ~
shoulder line
 Numbered C1-C7
 Smallest & lightest vertebrae
 Unique vertebrae
– Atlas or C1: no body; holds the occipital bone,
allows nodding motion (“yes”)
– Axis or C2: acts as a pivot for rotation; shake
head (“no”)
Thoracic Vertebrae
12 total; runs through mid-back
 Numbered T1-T12
 Larger than cervical
 Longer, palpable spinous processes
 Ribs attach here posteriorly

Lumbar Vertebrae

5 total
 Numbered L1-L5
 Huge bodies and
short spinous
processes
 Holds most of body
weight & stress; very
sturdy
Sacrum &
Coccyx

Sacrum
– Formed from 5 fused
vertebrae
– Numbered S1-S5
– Makes up posterior
wall of pelvis
– Strengthens &
stabilizes pelvis

Coccyx
– 4 fused vertebrae
Ligaments of the Spine

There are several; only 2 you need to
know
– Anterior Longitudinal Ligament: resists
back hyperextension
– Posterior Longitudinal Ligament: resists
back flexion
Intervertebral Discs
Cushion-like pads between vertebrae
 Asts as shock absorbers during motion
 Makes up ~25% of length of column
 Flattens during the day

Intervertebral Discs
Ribs




Flat bones
12 total pairs
Attach posteriorly to thoracic spine
Function:
– Protect thoracic organs

True Ribs: the superior 7 pairs
– Attach directly to sternum by costal cartilage

False Ribs: the inferior 5
– 8-10: join each other by cartilage and indirectly attach to
sternum
– 11& 12: the floating ribs, no anaterior attachment
Rib Cage
Pelvis
Has 2 regions: true and false pelvises
 False pelvis superior to true pelvis
 True pelvis dimensions are a concern
to child-bearing women
 Pelvic structure differs between men
and women

Gender Difference of Pelvis

Men
– Narrow outlet
– Heavier & thicker bone
structure
– Ilia less flared, more
vertical
– Sacrum long and curved
– Ischia close together
– Less rounded pubic arch

Women
– Inlet circular & large
– Pelvis shallow, lighter &
thinner
– Ilia flare laterally
– Sacrum shorter & less
curved
– Ischia farther apart &
shorter
– Pubic arch is more
rounded