LECTURE OUTLINE & REVIEW QUESTIONS
LECTURE OUTLINE: BONE
Bone: Definition
Special Supporting Connective Tissue
Matrix = extracellular (intercellular) material
Cells = Osteoblasts, Osteocytes, Osteoclasts
General Functions
Structural support
Protection
Muscle levers
Calcium reservoir
Bone marrow
Gross Structure of Bones
Flat bones: e.g., sternum, cranial bones, etc.
Short bones: e.g., carpals, tarsals
Sesamoid bones: develop in tendons
Patella, tendons of hand and foot
Long bones:
Upper Limb: humerus, radius, ulna, metacarpals, phalanges
Lower Limb: femur, tibia, fibula, metatarsals, phalanges
Terminology:
Proximal end (epiphysis)
Distal end (epiphysis)
Shaft (body, diaphysis)
Metaphysis
Irregular bones: e.g., vertebrae, many skull bones, scapula,
hip bone
Two Structural Forms of Bone
Compact (dense): external
Spongy (cancellous): internal
Trabeculae (s.=trabecula) + marrow spaces
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Covering & Lining Tissues of Bone
Periosteum (“around the bone”): fibrous c.t.
Envelops all external surfaces, except joint surfaces.
Outer fibrous layer + inner cellular (osteogenic) layer
Perforating (Sharpey’s) fibers:
Bundles of collagenous fibers
Anchor periosteum to bone matrix
Functions of periosteum:
Anchor tendons & ligaments to bone
Carry blood vessels & nerves supplying bone
Growth & repair
Endosteum (“within the bone”): delicate c.t.
Lines all internal surfaces
Bone Formation: The Basic Process
Look at process for single cell:
1. Mesenchymal stem (osteoprogenitor) cells 
differentiation  osteoblasts
2. Osteoblasts  organic matrix (osteoid tissue, ossein)
95%: Type I collagen fibers + 5%: glycosaminoglycans
and glycoproteins
3. Osteoblast and slender cell projections surrounded by
organic matrix.
4. Deposition of inorganic matrix: slender calcium salt
crystals
Precipitate from tissue fluids (not produced by
osteoblasts)
Mostly calcium phosphate (~ hydroxyapatite rock
crystals)
Same orientation as Type I collagenous fibers
5. Osteoblast surrounded by bone matrix = osteocyte
Space in matrix occupied by osteocyte cell body =
lacuna (pl. lacunae)
Tunnels through matrix occupied by cell processies =
canaliculi (s. = canaliculus)
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LECTURE OUTLINE & REVIEW QUESTIONS
Look at process for multiple cells:
1. “Rows” of osteoblasts connected by cell processes
2. Secretion of organic matrix
Sheets or lamellae (s. = lamella) of matrix between rows
of osteoblasts
Collagen fibers in adjacent layers +/- at right angles
3. Deposition of inorganic matrix (calcium salts)
Same orientation as collagen fibers
4. Final product:
Lamellae of bone matrix + “cement substance”
Rows of osteocytes in lacunae between lamellae
Lacunae connected with each other by canaliculi
Outermost canaliculi connect to bone surface
All bone (compact & spongy) is constructed of lamellae cemented
together.
Problem:
Osteocytes need nutrients, gases, waste removal, etc.
Bone matrix too dense for adequate diffusion.
Materials must diffuse through canaliculi.
Blood vessels  tissue fluids  canaliculi  osteocytes
in lacunae
Limits bone thickness (number of lamellae)
The farther from the bone surface, the longer the
diffusion time and the less the quality of the materials.
Solution: Spongy bone
Trabeculae thin (~ 3-5 lamellae).
Surrounded on all sides by blood vessels in marrow spaces.
Solution: Compact bone
Lamellae formed into cylinders surrounding a central blood
supply.
Osteon (“bone unit”) or Haversian System
Concentric lamellae (usually ~ 3-5)
Haversian canal: contains blood vessels and nerves
Osteons packed together to form compact bone.
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ANATOMY 25 - GUTHRIE
Angular spaces between osteons filled with interstitial
lamellae.
Fragments of older, reabsorbed ostons.
Outer and inner surfaces of compact bone smoothed by
circumferential lamellae.
Blood Supply
Nutrient artery or arteries  periosteal branches 
Volkmann’s canals  Haversian canal branches + branches
to endosteum and marrow spaces
Typical Long Bone Structure
Proximal & Distal Ends:
Core of spongy bone containing red (active) or yellow
(inactive) bone marrow
Trabeculae arranged to withstand tensile and compressive
forces
Lined with endosteum
Compact bone enclosing spongy bone
Joint cartilage covering joint surfaces
Periosteum covering non-joint surfaces
Shaft:
Cylinder of compact bone (with variable amounts of
internal spongy bone)
Covered externally with periosteum.
Medullary or marrow canal containing red or yellow bone
marrow
Lined with endosteum.
Short, Flat, and Irregular Bone Structure
Basically a core of spongy bone covered with compact bone.
Joint surfaces covered with joint cartilage.
Non-joint surfaces covered with periosteum.
Parts of some irregular bones may consist of compact bone
only; e.g., body of scapula.
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LECTURE OUTLINE & REVIEW QUESTIONS
In cranial bones, spongy bone is often referred to as diploe
(Greek for “spongy”).
Osteoclasts (“bone breakers”) and Bone Resorption
Large, multinucleated cells
Origin: monocytes (white blood cells)
Function: Bone matrix destruction (“resorption”)
How osteoclasts work
Podosomes (cell processes) attach cell to bone matrix
surface
Integrins & actin microfilaments
Part of cell membrane facing matrix = resorption
membrane.
“Ruffled border” increases contact surface area
Resorption membrane:
Release of lysosomal enzymes
Release of hydrogen ions (acid)
Result:
Breakdown of bone matrix.
Depression in bone matrix: Howship’s (resorption)
lacuna
Why ?
Bone is in constant flux: deposition  resorption
Bone Growth:
Remodeling: “woven bone”  spongy or compact bone
Maintenance of bone proportions
Responses to physical stresses: load, muscle tensions, etc.
Calcium concentrations
Dietary Ca++ intake  blood calcium levels
Blood Ca++  tissue fluids cells (critical functions)
Blood  calcium  bone
Bone Repair
Fracture  hematoma  fibrocartilage callus  woven
bone  remodeling to spongy & compact bone
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ANATOMY 25 - GUTHRIE
Hormonal Effects on Osteoclasts
Growth hormone, steroids, calcitonin, etc.
Bone Formation
Bone forms by replacing a pre-existing tissue.
1. Intramembranous Bone Formation (“membrane bone”)
Membrane = sheet of mesenchyme
Mesenchymal stem cells  osteoblasts
Osteoblasts  osteoid tissue depostion of calcium
salt crystals  bone matrix with trapped osteocytes 
plate of woven bone
Osteoblasts deposit more bone around initial plate 
expansion of woven bone
Remodeling (osteoblasts / osteoclasts)  spongy &
compact bone
2. Endochondral Bone Formation (“cartilage replacement
bone”)
Hyaline cartilage  cells hypertrophy & release
chemicals  cartilage matrix calcifies & cartilage cells
die
Result: empty lacunae surrounded by spicules of
calcified cartilage matrix
Blood vessels, osteoblasts, bone marrow cells invade
spaces in cartilage.
Osteoblasts lay down bone around calcified cartilage
spicules.
Cartilage eventually completely replaced by bone.
Osteoblasts / osteoclasts  remodeling  spongy &
compact bone
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LECTURE OUTLINE & REVIEW QUESTIONS
An Example: Developing Long Bone
1. Hyaline cartilage pre-bone model.
General shape & proportions of specific bone
All surfaces – except joints – covered with
perichondrium
2. Bone collar & Primary ossification center
Perichondrium around center of diaphysis 
periosteum
Stem cells  osteoblasts  intramembranous bone
Cartilage degeneration in centero of diaphysis 
primary ossification center
3. Periosteal blood vessels invade primary ossification
center
Osteoblasts & bone marrow cells follow vessels
Osteoblasts  bone (endochondral) replaces calcified
cartilage
4. Secondary (epiphyseal) ossification centers form
Blood vessels invade secondary centers
Osteoblasts & bone marrow cells follow vessels
Osteoblasts  bone (endochondral) replaces calcified
cartilage
5. Epiphyseal plate formation
Endochondral formation expands until only a thin
plate of cartilage separates diaphysis and epiphyses =
epiphyseal plate or growth cartilage
Growth continues as long as cartilage production
outstrips replacement by bone.
Epiphyseal closure = end of growth
Epiphyseal plate replaced by bone.
Synostosis of epiphyses and diaphysis
6. During growth period, osteoblast / osteoclast activity:
Remodels woven to spongy or compact bone
Maintains proper bone proportions
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ANATOMY 25 - GUTHRIE
REVIEW QUESTIONS
1. The sternum, ribs, and bones forming the cranium are
examples of _?_ bones. (a) short (b) flat (c) long (d)
irregular (e) none of these
2. Most bones of the limbs are _?_ bones. (a) short (b) flat
(c) long (d) irregular (e) none of these
3. The vertebrae and the hip bones are examples of _?_ bones.
(a) short (b) flat (c) long (d) irregular (e) none of these
4. The carpals and tarsals are examples of _?_ bones. (a) short
(b) flat (c) long (d) irregular (e) none of these
5. Short bones that develop in muscle tendons are called _?_ .
(a) sesamoid (b) endochondral (c) patellae (d) diploe (e)
osteoid
6. In mature flat bones, the internal spongy bone is called _?_.
(a) osteoid (b) endosteum (c) diploe (d) periosteum (e)
woven
7. The shaft of a long bone is also called the: (a) proximal
epiphysis (b) medullary canal (c) diaphysis (d) distal
epiphysis (e) hypophysis
8. The marrow space in the shaft of a long bone is called the
_?_. (a) perforating canal (b) Haversian canal (c)
medullary cavity (d) central canal (e) diastema
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LECTURE OUTLINE & REVIEW QUESTIONS
ANATOMY 25 - GUTHRIE
9. Which of the following statements about bone is not true ?
a. All external, non-articular surfaces of bones are
covered with periosteum
b. All internal surfaces are lined with endosteum
c. All internal spaces are filled with either red or
yellow bone marrow.
d. All bone develops by endochondral ossification.
e. All mature bone is basically contructed of sheets of
matrix called lamellae.
12. Which of the following is not associated with spongy bone
? (a) trabeculae composed of lamellae (b) spaces lined with
endosteum (c) periosteum (d) osteocytes in lacunae
connected by canaliculi (e) marrow spaces filled with
yellow or red bone marrow
10. Which of the following statements about bone is not
correct ?
a. Bone matrix consists of organic and inorganic
components.
b. The organic matrix of bone consists of ground
substance and collagenous fibers.
c. The organic matrix of bone is produced by
osteoblasts.
d. The inorganic matrix consists mostly of calcium
phosphate crystals.
e. The inorganic matrix is produced and maintained
by osteoclasts.
14. Osteoclasts _?_. (a) are derived from monocytes (b)
release acids and enzymes that break down bone matrix (c)
phagocytize collagen fibers and dead osteocytes (d) all of
these (e) none of these
11. Which of the following statements about osteons is not
correct ?
a. Osteons are composed of concentric lamellae.
b. Osteons are found only in bones that develop by
replacing cartilage.
c. The Haversian or central canal contains blood
vessels and nerves.
d. Blood vessels enter osteons by way of Volkmann's
or perforating canals.
e. Nutrients travel from the Haversian canal to
osteocytes through canaliculi.
Anatomy 25.mguthrie
13. Which of the following is not found in both spongy and
compact bone ? (a) osteocytes (b) osteons (c) canaliculi
(d) lamellae (e) lacunae
15. Osteoclasts _?_. (a) work with osteoblasts to remodel and
reshape growing bones (b) work with osteoblasts to repair
bones (c) are responsible for releasing calcium from bone
matrix (d) all of these (e) none of these
16. Periosteum: (a) is an anchoring site for tendons and
ligaments (b) contains blood vessels and nerves that supply
the bone (c) is anchored to the bone matrix by Sharpey's
fibers (d) all of these (e) none of these
17. The inner layer of periosteum _?_. (a) contains stem cells
that can become osteoblasts (b) is necessary for the repair
of bone fractures (c) is involved in bone growth (d) all of
these (e) none of these
18. Which of the listed events occurs thirdly during
osteogenesis or ossification ? (a) osteoblasts secrete osteoid
tissue (b) mesenchymal cells convert to osteoblasts (c)
calcium salt crystals form in and around collagenous fibers
(d) osteoblasts become trapped in lacunae connected by
canaliculi (e) osteocytes maintain the surrounding matrix
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LECTURE OUTLINE & REVIEW QUESTIONS
ANATOMY 25 - GUTHRIE
19. Which of the listed events occurs fourthly during
intremembranous ossification ? (a) mesenchymal cells
convert to osteoblasts (b) osteoblasts and osteoclasts
convert woven bone to spongy and compact bone (c)
osteoblasts secrete osteoid tissue (d) calcium salts
precipitate in and around collagenous fibers (e) a mass of
woven bone begins to form
20. Which event does not occur in endochondral bone
formation ?
a. Cartilage cells hypertrophy and release substances
that cause the matrix to calcify.
b. Cartilage cells die, the matrix degenerates, and
spaces appear in the matrix.
c. Blood vessels, dragging osteoblasts and marrow
cells, invade the spaces.
d. Osteoblasts convert the calcified cartilage matrix to
bone.
e. Osteoblasts lay down bone around the degenerating
cartilage matrix.
21. In a growing long bone, the epiphyses and the diaphysis
are separated by _?_. (a) epiphyseal plates (b) primary
ossification centers (c) a bone collar (d) secondary
ossification centers (e) fibrocartilage (d) all of these (e)
none of these
22. Which of the following occurs in terminating the growth
of long bones ? (a) chondroblasts stop dividing mitotically
(b) no new cartilage matrix is formed (c) osteoblasts
replace the existing cartilage with bone (d) the epiphysis
and the diaphysis synostose (e) all of these
Anatomy 25.mguthrie
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