Anatomy Notes
Chapter 6
I. cartilage
A. perichondrium
1. outer fibrous layer contains fibroblasts that secrete collagen
2. inner chondrogenic layer contains cells that can proliferate and turn into
chondroblasts
B. cartilage growth
1. appositional growth
chondroblasts add new layers of matrix on the outside of an existing piece
of cartilage
2. interstitial growth (young cartilage only)
chondrocytes inside a piece of cartilage divide, and then secrete new
matrix, spreading themselves apart
II. bone
A. types of bone tissue
1. compact / lamellar bone tissue forms the outer surfaces of all bones
very dense, has few spaces
2. cancellous / woven / spongy bone tissue is found inside all bones
not very dense, has many spaces
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Anatomy Notes
Chapter 6
B. membranes associated with bones
1. periosteum - layer of tissue that covers the outside surface of all bones except
where there is articular cartilage
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provides a connecting point for tendons, ligaments and joint capsules
is connected to underlying bone by perforating fibers
a. outer layer - dense irregular c.t.
b. inner layer - contains osteoblasts and osteoclasts
2. endosteum = thin layer that lines all inner spaces inside bones, similar to inner
layer of periosteum
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covers trabeculae in cancellous bone
lines central and perforating canals in dense bone
lines medullary cavity
C. gross structure
1. long bones
a. diaphysis = shaft
b. epiphysis/epiphyses = ends
epiphyseal line = where diaphysis and epiphyses fuse (visible inside bone)
c. medullary cavity = space inside diaphysis containing bone marrow
2. flat bones
diploe
D. distribution of compact and spongy bone
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compression stress = force that pushes on bone along its axis
tension stress = force that pushes perpendicular to axis of bone
stress is greatest at the outer edge of the bone and decreases towards the
middle
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Anatomy Notes
Chapter 6
E. microscopic structure of bone tissue
1. both types of bone tissue have:
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osteocytes – mature bone cells surrounded by matrix, located between
lamellae
lacuna/lacunae – space in which an osteocyte is found
canaliculi – tiny canals connecting lacunae and osteocytes to each other; they
go through the lamellae
lamella/lamellae – layer of bone matrix
2. compact bone
o osteon = structural unit, runs parallel to axis of bone or stress lines
o central (Haversian) canals = in center of osteon, contain blood vessels and
nerves
in osteons, lamellae form concentric circles around the central canal
o circumferential lamellae = layers of bone matrix that occur outside the
osteons; found on extreme outer and inner surfaces of bones
o perforating (Volkmann's) canals = perpendicular to central canals, contain
blood vessels that branch into smaller vessels in the central canals
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Anatomy Notes
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3. cancellous / spongy / trabecular bone
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trabeculae = small irregular and connected pieces of bone tissue
in trabeculae, lamellae are arranged in irregular layers
the spaces between trabecular contain bone marrow
F. chemical composition
1. organic matrix (osteoid) = cells and collagen
35% of tissue mass
tensile strength
2. inorganic matrix = hydroxyapatite (calcium phosphate and other mineral salts)
65% of tissue mass
deposited as tiny crystals around collagen fibers
compression strength
G. bone formation (osteogenesis or ossification)
1. intramembranous ossification - skull (except temporal, occipital, ethmoid,
sphenoid) and clavicle
a. mesencyme cells form c.t. membranes where bones are to be formed
b. some mesencyme cells differentiate into osteoblasts and begin to
secrete bone matrix
c. calcium salts deposit around the osteoid and trap the osteoblasts
d. trabeculae enlarge and fuse with each other to form cancellous bone
e. the inner and outer surfaces are remodeled into compact bone
f. mesencyme forms a periosteum on the outer surfaces and endosteum
on the inside
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Anatomy Notes
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2. endochondral – all other bones
a. hyaline cartilage model in fetus
b. bone collar around middle of cartilage cuts off diffusion, cartilage
disintegrates
c. periosteal bud brings blood vessel and bone cells into cartilage model
(primary ossification center)
d. cartilage model grows and is gradually replaced by bone tissue
e. secondary ossification centers form in epiphyses
f. epiphyseal plates are disks of hyaline cartilage between the primary and
secondary ossification centers
H. bone growth
1. long bones
a. length - at first, epiphyseal plates expand faster than they are replaced
by bone (this is caused mainly by growth hormone)
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Anatomy Notes
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b. diameter  appositional growth adds new layers to the outside
 at the same time, osteoclasts removed tissue from the inner surface
2. flat bones - new tissue is added around the edges
3. why long bones grow and then stop growing
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gonadal steroid hormone secretion begins at puberty
these hormones cause increased growth in both bone and cartilage, but
faster growth in bone
closure of the epiphyseal plates causes bones to stop growing longer
I. remodeling - bone removal and replacement
1. process
 osteoclasts secrete acid to dissolve the calcium salts and then use
enzymes to remove the collagen
 osteoblasts deposit new bone tissue
2. causes
a. change in blood calcium levels
b. change in stress on bones
 change in weight
 change in muscle tone
 change in activity level
J. fracture repair
1. fracture hematoma
2. fibrocartilage callus
3. bony callus - cartilage is replaced by spongy bone
4. remodeling
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