Chapter 6- Part I
Bones and Skeletal Tissues
• Components of the skeletal system
• Classification of Bone (bone shapes)
• Functions of bone
• Bone structure
• Microscopic structure of bone and bone cells
What are the parts of the skeletal
system?
• Bones of the skeleton
– The 206 bones of the body are divided into
two categories:
– The axial skeleton and the
– The appendicular skeleton
• Cartilage, ligaments, and other connective
tissue that stabilize or connect bones
The bones and
cartilages of the
skeleton
Growth of Cartilage
• Appositional – cells in the perichondrium secrete
matrix against the external face of existing
cartilage
• Interstitial – lacunae-bound chondrocytes inside
the cartilage divide and secrete new matrix,
expanding the cartilage from within
• Calcification of cartilage occurs
– During normal bone growth
– During old age
Notes on perichondrium
• A fibrous membrane covering the external surface of
cartilaginous structures
• The perichondrium nourishes the avascular cartilage, and it
also contains mesenchymal cells which can differentiate into
chondroblasts. Growth from the perichondrium is
appositional growth.
perichondrium
chondroblast
Bones come in many shapes
(a) Long bone
(humerus)
(b) Irregular bone
(vertebra), right
lateral view
(c) Flat bone
(sternum)
(d) Short bone
(talus)
What are some of the functions of bone?
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Support
Protection
Movement/leverage
Storage of minerals/fat
Blood cell production
Gross anatomy of bonesBone markings
• Bone surfaces are rarely smooth- they display
projections, depressions and openings
• WHY?
• Projections (or elevations)
– Tuberosity, crest, process, crest, spine, condyle etc, etc.
• Depressions, grooves, openings in bone
– Fossae, sulcus, foramen, grooves, canal, etc.
• These are fixed landmarks
Landmarks
of the Humerus
Parts of the humerus - head,
surgical neck, greater tubercle,
lesser tubercle, lateral
epicondyle, medial epicondyle,
trochlea, capitulum, coronoid
fossa, olecranon fossa, deltoid
tuberosity
Compact and Spongy Bone
• Each bone in the skeleton contains both
compact bone and spongy bone.
compact bone
trabeculae
Compact bone link
spongy bone
Bone structure
• Let’s first take a look at the
structure of a typical long bone
• Then we’ll cover/compare the
structure of long bones to short,
irregular, and flat bones
Structure of long bones
• Diaphysis- tubular shaft, with wall
made of compact bone, and a true
marrow cavity inside
• Epiphysis- each ‘swollen’ end of the
bone. Composed largely of spongy
bone, with a thin, outer layer of
compact bone
– The joint surfaces of each epiphysis
is covered with hyaline (articular)
cartilage
• Between the epiphysis and diaphysis (in
adult bone)is the epiphyseal line
Bones have membranes- the
periosteum and the endosteum
Periosteum (Periosteum)
• Covers outer surface of all bones,
except at joint surfaces
• Isolates bone from surrounding
tissue
• Route for nerves and blood supply
• Provides an insertion point for
tendons/ligaments
• Actively participates in bone growth
and repair
• A double membrane with an outer
fibrous layer (dense irregular CT)
and an inner cellular layer
– Osteoblasts- bone grows thicker
Endosteum (Endosteum)
• Covers internal bone surfaces
– Including: trabeculae,
marrow cavity and canals
within compact bone
• Contains bone-forming cells,
bone destroying cells and
stem cells (osteoprogenitor)
cells
• Active in bone growth, repair
and remodeling
Bone Cells
• Cells:
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Osteoblasts – bone-forming cells
Osteocytes – mature bone cells
Osteoprogenitor cells – stem cells, grandfather cells
Osteoclasts – large cells that resorb or break down
bone matrix
– More to come
Structure of short, irregular, and
flat bones
• Consist of thin plates of compact bone on the
outside and spongy bone on the inside
• Contain bone marrow, but no formal marrow
cavity is present
• In flat bones, the internal
layer of spongy bone
..
is called diploe
• Where is the periosteum,
endosteum?
Where do you find marrow and
what is the function?
• Red marrow, hematopoietic tissue
• Yellow marrow
The microscopic structure of
compact bone
• Osteon- basic functional unit
• Osteocytes arranged around
central canal, between
concentric lamellae
– One small artery, one
venule, one nerve, parallel
with bone surface
• Perforating canal
– Perpendicular to long axis
of bone, connect blood
supply from periosteum
through to marrow cavity
• Interstitial lamellae
• Circumferential lamellae
Compact
bone
Spongy bone
Perforating
(Volkmann’s)
canal
Endosteum lining
bony canals
and covering
trabeculae
Central
(Haversian)
canal
Osteon
(Haversian
system)
Circumferential
lamellae
(a)
Perforating (Sharpey’s)
fibers
Lamellae
Periosteal blood vessel
Periosteum
Structure of compact bone
link
A SEM of compact bone
Functions of compact bone?
The structure of spongy bone
Canaliculi
opening to
surface
• Lamella not in osteons
• Trabeculae
• No capillaries within matrix
of spongy bone
• Nutrients reach osteocytes via
diffusion through canaliculi
that reach surface
• Trabeculae protect cells of
red marrow, yellow marrow
• Marrow is vascularized
Structure of spongy bone
Spongy bone
(diploë)
Compact bone
Trabeculae
Functions of spongy bone?
Link
http://depts.washington.edu/bonebio/ASBMRed/structure.html
Composition of Bone (osseous tissue)
• Remember that in all connective tissues, there are
cells, fibers and ground substance
• Cells
• Matrix- solid, collagen and Ca2+ deposits
– Osteoid makes up 1/3 of bone tissue = collagen fibers,
proteoglycans and glycoproteins
– Calcium phosphates account for 2/3 the weight of bone
– Form hydroxyapatite crystals
– Crystals lie in, around, and on
the collagen fibers. Fibers form
framework for crystals &
developing osteocytes
Cells of the Bone- Four major types
(a) Osteogenic cell
(b) Osteoblast
(c) Osteocyte
(d) Osteoclast
Stem cell
Matrix-synthesizing
cell responsible
for bone growth
Mature bone cell
that maintains the
bone matrix
Bone-resorbing cell
Lineage of bone cells
Who is missing?
Osteogenic (progenitor) cells
• Stem cells of the bone
• Produce daughter cells
that differentiate
into osteoblasts
– Cigarette smoke?
• Found in endosteum
and periosteum
Osteoblasts
osteoid
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Osteoblasts line all surfaces of bone
Osteoblasts are the builders!
Produce new osteoid
Differentiate into osteocytes
Osteoblasts have receptors for
estrogens
– Effects of estrogen on these cells?
Osteocytes
• Mature bone cells
• One osteocyte sits in a lacunae
• Cytoplasmic cellular extensions
reside in canaliculi
• Gap junctions connect
neighboring cells
– Allow for exchange of
nutrients/ions/waste, etc.
• Functions- maintain
protein/mineral content of
matrix, and bone repair
Osteoclasts
• Remove/resorb and recycle bone matrix
– Found largely in endosteum
• Giant cells, 50 or more nuclei
• Cousins of macrophage! Do not
arise from osteogenic cells
• Release acids and digestive enzymes onto matrix
• Important in bone remodeling and regulation of blood Ca2+
• Activity inhibited by estrogen
Homeostasis- A balance exists between
osteoblast and osteoclast activity
LINK
• If osteoblasts are working faster than osteoclasts,
what happens to bone?
• If osteoclasts are working faster, what happens to
bone? Breakdown > building? Blood calcium?