Chapter 5 “ The Skeletal System”
I. Bones
A. Function of bones
1. support
2. protection – protect soft
body organs.
3. Movement – skeletal
muscles attach to bones by
tendons.
4. Storage – fat is stored in
internal cavities; Ca and P.
5. Blood cell formation –
“hematopoiesis”
B. Classification of Bones
1. compact bones – dense,
looks smooth, homogeneous.
2. Spongy bones – composed
of small needlelike pieces of
bone and a lot of open spaces.
3. Classified by shape –
a. long bones – longer than
they are wider. – have a shaft
w/heads at both ends. EX:
bones of limbs except wrist
and ankle.
b. Short bones – cube-shaped,
mostly spongy. Ex: bones of
ankle and wrist.
c. Flat bones – thin, flat,
usually curved two thin layers
of compact bone sandwiching
spongy bones. Ex: skull, ribs,
sternum (breast bone).
d. Irregular bones – bones that
do not fit into one of the
previous classes. Ex:
vertebrae.
4. Bone markings-
a. projections or processes –
grow out from bone surface.
b. Depressions or cavities –
indentations in the bone.
*Know table 5.1 Bone
markings.
C. Structure of Long bone
1. Gross Anatomy
a. diaphysis – shaft of long
bone – composed of compact
bone.
1. periosteum – fibrous
connective tissue covering
diaphysis. “sharpey’s
fibers” – connect it to
underlying bone.
b. epiphysis – ends of long
bone. – thin layer of compact
bone enclosing an area filled
w/spongy bone.
1. articular cartilage –
covers epiphyses- type of
hyaline cartilage.
2. Epiphyseal line –
remnant of epiphyseal plate
(hyaline cartilage) in young
growing bone. – plate
causes lengthwise growth of
a long bone.
c. Cavity of shaft – composed
of:
1. yellow marrow –
(medullary) – fat (adults)
2. infants – red marrow in
shaft (red blood cells form)
3. adults – red marrow
confined to cavities of
spongy tissue (bone), flat
bones and epiphysis of
some long bones.
2. Microscopic anatomy
a. compact bone – filled w/
passageways carrying nerves,
blood vessels – provide living
bone w/ nutrients.
1. osteocytes – mature bone
cells found in tiny cavities
w/in matrix called lacunae.
2. Lamellae – concentric
circles of lacunae.
3. Central (haversian)
canals – canal in center of
Haversian system.
4. Osteon or Haversian
system – complex consists
of central canal and matrix
rings.
5. Canaliculi – tiny canals
which radiate outward from
central canal.
6. Perforating (Volkman’s
canals) – run into compact
bone at right angles.
D. Bone Formation, growth, and
remodeling
1. ossification – process of
bone formation
Two major steps:
a. hyaline cartilage is
covered with bone matrix
by osteoblasts . (bone
forming cells)
b. enclosed hyaline
cartilage is digested away,
opening up a medullary
cavity within the newly
formed bone.
2. Long Bone growth – “new”
cartilage forms on the ends of
bone. (epiphyseal plate).
“Old” cartilage near the
medullary cavity is broken and
replaced by bone.
3. Bones are remodeled
continuously.
Two factors of change:
a. calcium levels in blood.
b. Pull of gravity and
muscles on skeleton
- low levels of calcium in
blood trigger parathyroid
glands to produce
parathyroid hormones
(PTH). PTH activates 
osteoclasts –giant bone
destroying cells in bone 
break down bone matrix to
release calcium into blood.
– certain bones are
increased in mass because
of the pull on them.
E. Bone Fractures
1. simple – bone breaks
completely
2. compound – broken ends of
the bone protrude through soft
tissue and skin.
3. Comminuted – bone breaks
into many fragments
4. Compression – bone is
crushed
5. Depressed – broken bone
portion is pressed inward.
6. Impacted – broken bone
ends are forced into each other.
7. Spiral – ragged break occurs
when excessive twisting forces
are applied to a bone.
8. Greenstick – bone breaks
incompletely. (like a green
twig of a plant)