The Skeletal System
Chapter 6
The Skeletal System
The skeletal system includes:
 Bones
 Cartilages
 Joints
(articulations)
 Ligaments
 Other connective tissues
The Skeletal System
Functions of the Skeletal System
 Support
 Protection
 Movement
(Leverage)
 Storage

__________

__________
 Blood
cell production
The Structure of a Typical Bone
All bones have a combination of spongy & compact
bone tissue
Figure 6-3(a)
The Histological Features of Spongy Bone

Lamellae (layers) of matrix laid down in __________ criss-crossing network of bony tissue
 Osteocytes located within lacunae
 Canaliculi branch out from lacunae
 Many marrow cavities which contain red marrow & small blood
vessels
The Histological Features of Compact Bone
______________ - basic functional unit
of compact bone
Concentric lamellae (layers) of matrix
surrounding central (Haversian) canal
Osteocytes located within lacunae
Canaliculi branch out radially from lacunae
_____________ (containing BVs)
run vertically down the length of the
bone
_________________ (containing
BVs) run horizontally across the width
Bone Cells
In addition to Osteocytes, the mature bone cells
found within the matrix of bone tissue, there are
three other cells that are associated with bones
 Osteoprogenitor cells
 Osteoblasts
 Osteoclasts
Bone Cells

Osteoprogenitor cells

Derived from mesenchymal cells
 Can undergo mitosis
 Mature into osteoblasts
Bone Cells

Osteoblasts
for osteogenesis –
 Mature into osteocytes
 Responsible
Bone Cells

Osteoclasts
 Derived
from embryological WBCs
 Secrete enzymes for osteolysis –
 Necessary for:
Anatomical Classification of Bones
Bones are classified by their basic shape
 Long bones
(e.g. humerus, femur)
Anatomical Classification of Bones
Short bones
(e.g. carpals, tarsals)

Anatomical Classification of Bones
 Flat bones
(e.g. parietal bone)
Anatomical Classification of Bones
 Irregular bones
(e.g. vertebra)
Anatomical Classification of Bones
Sesamoid bones
(e.g. patella)

The Structure of a Typical Long Bone
diaphysis (compact bone)
Figure 6-2
The Structure of a Typical Long Bone
epiphysis (spongy bone)
diaphysis
epiphysis
The Structure of a Typical Long Bone
articular cartilage
epiphysis
diaphysis
epiphysis
articular cartilage
The Structure of a Typical Long Bone
epiphysis
metaphysis – location of
• epiphyseal plate – in children
• epiphyseal line – in adults
diaphysis
metaphysis
epiphysis
articular cartilage
The Structure of a Typical Long Bone
medullary cavity
• filled with yellow marrow in adults
• lined with endosteum
The Structure of a Typical Long Bone
Double layered
membrane
surrounding bone
(except at articular
cartilage)
periosteum Inner cellular layer
contains:
_______________
Outer fibrous layer
of dense irregular
CT for:
________________
Bone Formation and Growth
Ossification - Process of converting other
tissues to bone
Two types of ossification processes occur
during embryological formation:
 Intramembranous
 Endochondral
Intramembranous Ossification





Forms flat bones of skull, mandible, clavicle
Replacement of mesenchymal membrane with osseous tissue
Mesenchymal cells differentiate to osteoprogenitor cells, which then
become osteoblasts
Osteoblasts create spongy bone tissue, which then remodels into
compact bone where necessary
Other mesenchymal cells around the developing bone form the
periosteum
Mesenchymal
tissue forms
Osteoblasts begin to
secrete osteoid
forming spongy
bone tissue
Blood vessels infiltrate
tissue. Calcium salts deposit
in osteoid. Periosteum
develops
Endochondral Ossification
 Most bones formed this way
 Mesenchyme creates Cartilage model, which gets replaced by bone
 Replacement begins in middle (diaphysis) & follows in ends
(epiphyses)
Chondrocytes at
the center of the
growing cartilage
model enlarge
and then die as
the matrix
calcifies.
Newly derived
osteoblasts cover
the shaft of the
cartilage in a thin
layer of bone.
Blood vessels
penetrate the
cartilage. New
osteoblasts form a
primary ossification
center.
The bone of the
shaft thickens,
and the cartilage
near each
epiphysis is
replaced by shafts
of bone.
Articular
cartilage
Enlarging
chondrocytes within
calcifying matrix
perichondrium
Epiphysis
periosteum
Diaphysis
Marrow
cavity
Primary
ossification
center
Bone
formation
Cartilage
model
Perichondrium now
called periosteum
Blood
vessel
Epiphyseal
cartilage
Marrow
cavity
Blood
vessel
Secondary
ossification
center
Bone Growth
Interstitial growth
 Occurs throughout childhood as long as
epiphyseal plate cartilage remains
 Replacement of cartilage by osseous tissue
(ossification) at __________ end of plate;
replacement of cartilage cells at _________end
of plate
 eventually no more cartilagenous growth
resulting in epiphyseal line
Appositional growth
 Occurs throughout life through activity of cells in
periosteum and endosteum
 important in repair and remodeling
Injury and Repair
Fracture - A crack or break in a bone
 Steps in fracture repair
 Fracture
hematoma - bleeding in bone tissue
causes a clot; occurs within hours
 Callus
formation - Mitoses in cells of periosteum,
endosteum forms internal & external callus of spongy
bone tissue; occurs within few days
 Bone
remodeling - replacement of spongy bone
with compact bone; occurs over months to years
Steps in the Repair of a Fracture
Immediately after the fracture,
extensive bleeding occurs. Over
a period of several hours, a large
blood clot, or fracture hematoma,
develops.
Bone
fragments
An internal callus forms as a
network of spongy bone
unites the inner edges, and
an external callus of cartilage
and bone stabilizes the outer
edges.
Spongy bone Cartilage
of internal of external
callus
callus
The cartilage of the
external callus has been
replaced by bone, and
struts of spongy bone
now unite the broken
ends. Fragments of dead
bone and the areas of
bone closest to the break
have been removed and
replaced.
External
callus
Fracture
hematoma
Dead
bone
A swelling initially
marks the location of
the fracture. Over time,
this region will be
remodeled, and little
evidence of the
fracture will remain.
New
bone
Periosteum
Internal
callus
External
callus
The Skeleton
Figure 6-8(a)
An Overview of the Skeleton
There are 206 bones in the adult human body
Skeletal Divisions


Axial skeleton (80 bones)
 Skull
 Thoracic cage and sternum
 Vertebral column
Appendicular skeleton (126 bones)
 Upper, lower limbs
 Pectoral girdle
 Pelvic girdle
Bone Markings (Surface Features)

Surface Features of Bones
Table 6-1 (in textbook)
Bone Markings (Surface Features)
Depressions/openings:
 fossa
 foramen (canal)
 sulcus(groove)
 meatus
Spinous
process
Transverse
process
Bone Markings (Surface Features)
Processes for articulations:



head
condyle
facet
Bone Markings (Surface Features)
Spinous
process
Processes for
attachment:
Transverse
process







Trochanter (only on femur)
tubercle
tuberosity
epicondyle
crest
spine
spinous process (SP) (only
on vertebrae)
 transverse process (TP)
(only on vertebrae)
Lateral epicondyle