1. Chapter 6: Osseous Tissue & Bone Structure

2. Homeostasis Provides support & protection Produces blood cells
Stores minerals & triglycerides

3. Functions of Bone Support Protection Assistance in movement
Structural framework of body
Supports soft tissue & provides attachment points for muscles
Protection
Protects important organs with rib cage & skull
Assistance in movement
Muscles attached to bones & pull on them
Mineral homeostasis
Stores several minerals, Ca2+ & P
Release on demand
Blood cell production
In red bone marrow
Triglyceride storage
In yellow bone marrow

4. An Introduction to Bone Markings
Openings
Sinus:
Chamber within a bone,
normally filled with air
Elevations and
Projections
Foramen:
Rounded passageway
for blood vessels
and/or nerves
Process:
Projection or
bump
Fissure:
Deep furrow, cleft, or slit
Ramus:
Extension of a bone
that forms an angle
with the rest of the
structure
Meatus:
Passage or channel,
especially the opening
of a canal
Skull, anterior view
Canal:
Duct or channel
Skull, lateral view
Processes formed
where tendons or
ligaments attach
Processes formed where
joints (articulations) occur
between adjacent bones
Trochanter:
Large, rough
projection
Head:
Expanded articular end
of an epiphysis, often
separated from the
shaft by a narrower
neck (see Figure 6–3a)
Crest:
Prominent
ridge
Spine:
Pointed
process
Neck:
Narrow connection
between the
epiphysis and
diaphysis (see
Figure 6–3a)
Head
Line:
Low ridge
Femur
Tubercle:
Small,
rounded
projection
Pelvis
Neck
Depressions
Facet:
Small, flat
articular surface
Sulcus:
Narrow
groove
Tuberosity:
Rough
projection
Fossa:
Shallow
depression
Humerus
Condyle:
Smooth, rounded
articular process
Trochlea:
Smooth, grooved
articular process
shaped like a pulley
Condyle

5. Bone Structure a The structure of a representative
Epiphysis
Spongy
bone
Metaphysis
Compact
bone
Diaphysis
(shaft)
Medullary
cavity
Metaphysis
Epiphysis
Cortex
(compact bone)
Diploë
(spongy bone) a
The structure of a representative
long bone (the femur) in
longitudinal section b
The structure of a flat bone
(the parietal bone)

6. The Periosteum and Endosteum
Circumferential
lamellae
Periosteum
Endosteum
Fibrous layer
Osteoclast
Cellular layer
Bone matrix
Osteocyte
Canaliculi
Osteogenic
cell
Osteocyte
in lacuna
Osteoid
Perforating
fibers
Osteoblast a
The periosteum contains outer
(fibrous) and inner (cellular) layers.
Collagen fibers of the periosteum are
continuous with those of the bone,
adjacent joint capsules, and attached
tendons and ligaments. b
The endosteum is an incomplete
cellular layer containing
osteoblasts, osteogenic cells,
and osteoclasts.

7. Composition of Bone Hardness due to inorganic minerals
Bone Contains
Organic
compounds
(mostly collagen)
33%
Calcium 39%
Potassium 0.2%
Sodium 0.7%
Magnesium 0.5%
Carbonate 9.8%
Phosphate 17%
Total inorganic 67%
components
99% of the body’s Calcium
4% of the body’s Potassium
35% of the body’s Sodium
50% of the body’s Magnesium
80% of the body’s Carbonate
99% of the body’s Phosphate
Hardness due to inorganic minerals
Flexibility due to collagen

8. Types of Bone Cells Canaliculi Osteocyte Matrix Matrix Osteoid
Osteoblast
Osteoblast: Immature bone cell
that secretes osteoid, the organic
component of bone matrix
Osteocyte: Mature bone cell
that maintains the bone matrix
Osteogenic
cell
Osteoclast
Matrix
Medullary
cavity
Medullary
cavity
Endosteum
Osteogenic cell: Stem cell whose
divisions produce osteoblasts
Osteoclast: Multinucleate cell
that secretes acids and enzymes
to dissolve bone matrix

9. Osteoprogenitor Cells
Unspecialized stem cells derived from mesenchyme
Undergo cell division producing osteoblasts
Osteogenic
cell
Medullary
cavity
Endosteum
Osteogenic cell: Stem cell whose
divisions produce osteoblasts

10. Osteoblasts Osteoblast: Immature bone cell
Bone building cells
Synthesize & secrete collagen & other organic components for matrix
Osteoblast: Immature bone cell
that secretes osteoid, the organic
component of bone matrix
Matrix
Osteoid
Osteoblast

11. Osteocytes Canaliculi Osteocyte Matrix Osteocyte: Mature bone cell
Mature bone cells that maintain daily metabolism
No cell division
Canaliculi
Osteocyte
Matrix
Osteocyte: Mature bone cell
that maintains the bone matrix

12. Osteoclasts Osteoclast: Multinucleate cell
Derived from fusion of macrophages
Mostly in endosteum
Digests bone tissue, called resorption
Osteoclast: Multinucleate cell
that secretes acids and enzymes
to dissolve bone matrix
Matrix
Osteoclast
Medullary
cavity

13. The Structure of Compact Bone
Central
canal
Venule
Circumferential
lamellae
Capillary
Concentric
lamellae
Osteons
Periosteum
Perforating
fibers
Endosteum
Interstitial
lamellae
Concentric
lamellae
Trabeculae of
spongy bone
(see Fig. 6–7)
Collagen
fiber
orientation
Vein
Artery
Arteriole
Central
canal
Perforating
canal a
The organization of osteons
and lamellae in compact bone b
The orientation of collagen
fibers in adjacent lamellae

14. Figure 6-5 The Histology of Compact Bone.
Central canal
Osteon
Canaliculi
Lacunae
Concentric
lamellae
Central
canals
Osteon
Lamellae
Lacunae
Osteon
LM × 343
Osteons
SEM × 182 a
A thin section through
compact bone. By this
procedure the intact matrix
making up the lamellae
appear white, and the central
canal, lacunae, and canaliculi
appear black due to the
presence of bone dust. b
Several osteons in
compact bone.

15. The Structure of Spongy Bone
Trabeculae of
spongy bone
Canaliculi opening
on surface
Endosteum
Lamellae

16. Figure 6-8 The Distribution of Forces on a Long Bone.
Body weight
(applied force)
Tension on
lateral side
of shaft
Compression
on medial side
of shaft

17. Figure 6-13 The Blood Supply to a Mature Bone.
Vessels in Bone
Articular
cartilage
Epiphyseal
artery and vein
Metaphyseal
artery and vein
Branches of
nutrient artery
and vein
Periosteum
Compact
bone
Nutrient artery
and vein
Medullary
cavity
Periosteal
arteries and veins
Nutrient
foramen
Periosteum
Connections to
superficial osteons
Metaphysis
Metaphyseal
artery and vein
Epiphyseal
line

18. Ossification Bone formation or osteogenesis Occurs
During initial formation in embryo
Endochondral
Intramembranous
For growth of bones
Remodeling of bones
Repair of fractures

19. Endochondral Ossification

20. Intramembranous Ossification1
Mesenchymal cells cluster
together, differentiate into
osteoblasts, and start to
secrete the organic
components of the matrix.
The resulting osteoid then
becomes mineralized with
calcium salts forming
bone matrix.
Bone matrix
Osteoid
Mesenchymal cell
Parietal bone
Ossification center
Blood vessel
Frontal
bone
Osteoblast
Occipital bone 2
As ossification proceeds,
some osteoblasts are
trapped inside bony
pockets where they
differentiate into osteo-
cytes. The developing bone
grows outward from the
ossification center in small
struts called spicules.
Spicules
Mandible
Intramembranous ossification
starts about the eighth week of
embryonic development. This
type of ossification occurs in
the deeper layers of the dermis,
forming dermal bones.
Osteocyte 3
Blood vessels begin to
branch within the region
and grow between the
spicules. The rate of bone
growth accelerates with
oxygen and a reliable
supply of nutrients. As
spicules interconnect, they
trap blood vessels within
the bone.
Blood vessel
trapped within
bone matrix 4
Continued deposition of
bone by osteoblasts
located close to blood
vessels results in a plate
of spongy bone with
blood vessels weaving
throughout. 5
Subsequent remodeling
around blood vessels
produces osteons typical
of compact bone.
Osteoblasts on the bone
surface along with
connective tissue around
the bone become the
periosteum.
Fibrous periosteum
Blood vessels
trapped within
bone matrix
Areas of spongy bone are
remodeled forming the
diploë and a thin covering of
compact (cortical) bone.
Cellular periosteum

21. Interstitial Growth 6
The epiphyses eventually become filled
with spongy bone. The metaphysis, a
relatively narrow cartilaginous region called
the epiphyseal cartilage, or epiphyseal
plate, now separates the epiphysis from the
diaphysis. On the shaft side of the
metaphysis, osteoblasts continuously
invade the cartilage and replace it with
bone. New cartilage is produced at the
same rate on the epiphyseal side.
Articular cartilage
Spongy
bone
Epiphyseal
cartilage
Diaphysis
Within the epiphyseal cartilage,
the chondrocytes are organized
into zones.
Chondrocytes at the
epiphyseal side of the
cartilage continue to
divide and enlarge.
Chondrocytes degenerate
at the diaphyseal side.
Osteoblasts migrate
upward from the diaphysis
and cartilage is gradually
replaced by bone.
Occurs at epiphyseal plate or growth plate in metaphysis
Growth in length
Layers of cartilage in 4 zones
Zone of resting cartilage
Anchors plate to epiphysis
Zone of proliferating cartilage
Chondrocytes dividing & grow
Zone of hypertrophic cartilage
Chondrocytes enlarge
Zone of calcified cartilage
Chondrocytes are dead due to calcification around them
Osteoclasts dissolve calcified cartilage
Osteoblasts lay down new bone tissue

22. Figure 6-10 Bone Growth at an Epiphyseal Cartilage.
An x-ray of growing
epiphyseal cartilages
(arrows) b
Epiphyseal lines in
an adult (arrows)

23. Appositional Growth
Growth in thickness
Occurs at periosteum

24. Bone Remodeling Replacement of old bone tissue with new
Involves bone resorption by osteoclasts & bone deposition by osteoblasts

25. Factors Affecting Growth & Remodeling
Minerals
Ca2+ P
Mg2+ Fl Mn
Vitamins
Vit A
Stimulates osteoblasts
Vit C
Needed for collagen
Vit D
For absorption of Ca2+
Vit K & B12
Synthesis of bone proteins
Hormones
Insulin-like growth factors from hGH
Stimulates osteoblasts & protein synthesis
Thyroid
Stimulates osteoblasts
Insulin
Synthesis of proteins
Sex hormones
Weight bearing exercise
Bones respond to stresses placed on them
Helps maintain density

26. Table 6-1 Hormones Involved in Bone Growth and Maintenance.

27. Calcium Homeostasis Bones stores about 99% of body’s Ca2+
Ca2+ needed for
Nerve & muscle function
Blood clotting
Cofactor for many enzymes
Blood level is closely regulated at 9-11 mg/dl

28. Low Calcium Ion Levels in Blood Calcium absorbed quickly
Figure 6-15a Factors That Alter the Concentration of Calcium Ions in Blood. a
Factors That Increase Blood Calcium Levels
These responses are triggered
when blood calcium ion
concentrations decrease
below 8.5 mg/dL.
Low Calcium Ion Levels in Blood
(below 8.5 mg/dL)
Parathyroid Gland Response
Low calcium levels cause the
parathyroid glands to secrete
parathyroid hormone (PTH).
PTH
Bone Response
Intestinal Response
Kidney Response
Osteoclasts stimulated to
release stored calcium ions
from bone
Rate of
intestinal
absorption
of calcium
increases
Kidneys retain
calcium ions
Osteoclast
more
Bone
calcitriol
Calcium released
Calcium absorbed quickly
Calcium conserved
Decreased calcium
loss in urine
Ca2+
levels in
blood
increase

29. High Calcium Ion Levels in Blood Calcium absorbed slowly
Figure 6-15b Factors That Alter the Concentration of Calcium Ions in Blood. b
Factors That Decrease Blood Calcium Levels
These responses are triggered
when blood calcium ion
concentrations increase above
11 mg/dL.
High Calcium Ion Levels in Blood
(above 11 mg/dL)
Thyroid Gland Response
Parafollicular cells (C cells) in the
thyroid gland secrete calcitonin.
Calcitonin
Bone Response
Intestinal Response
Kidney Response
Osteoclasts inhibited while
osteoblasts continue to lock
calcium ions in bone matrix
Rate of
intestinal
absorption
of calcium
decreases
Kidneys
allow
calcium
loss
less
Bone
calcitriol
Calcium absorbed slowly
Calcium excreted
Calcium stored
Increased calcium
loss in urine
Ca2+
levels in
blood
decrease

30. Fracture Any break in a bone Repair process divided into 4 phases
Establishment of a fracture hematoma
Soft callus formation
Hard callus formation
Remodeling

31. Fracture Hematoma 1 Fracture hematoma formation. Fracture hematoma
Dead bone
Bone fragments 1
Fracture hematoma
formation.

32. Soft Callus Formation 2 Callus formation. Spongy bone of Cartilage of
internal callus
Cartilage of
external callus
Spongy bone of
external callus
Periosteum 2
Callus formation.

33. Bony Callus Formation 3 Spongy bone formation. Internal callus
External callus
Spongy bone formation. 3

34. Remodeling Phase
External
callus 4
Compact bone
formation.

35. Types of Fractures Transverse fracture Spiral fracture
Displaced fracture
Compression
fracture
Epiphyseal fracture
Comminuted
fracture
Pott’s fracture
Greenstick fracture
Colles fracture

36. Effects of Aging Loss of bone mass Brittleness From demineralization
From decreased rate of protein synthesis
Lose tensile strength from lack of collagen

37. Osteoporosis Bone resorption outpaces bone deposition
Risk factors include
Woman
Family history
European or Asian descent
Thin or small build
Inactive
Cigarette smoker
Diet low in Ca2+ & vit D
More than 2 alcoholic drink/day
Early menopause
Normal spongy
bone
SEM × 25
Spongy bone in
osteoporosis
SEM × 21

38. Figure 6-1 A Classification of Bones by Shape.
(a) Sutural Bones
(d) Flat Bones
Sutural bones, or
Wormian bones, are
small, flat, oddly
shaped bones found
between the flat bones
of the skull. They range
in size from a grain of
sand to a quarter. Their
borders are like pieces
of a jigsaw puzzle.
Sutural
bone
Flat bones have thin, parallel surfaces. Flat bones
form the roof of the skull, the sternum (breastbone),
the ribs, and scapulae (shoulder blades). They
provide protection for underlying soft tissues and
offer an extensive surface area for the attachment
of skeletal muscles.
Sutures
Parietal bone
Sectional
view
(b) Irregular Bones
(e) Long Bones
Irregular bones have
complex shapes with
short, flat, notched, or
ridged surfaces. The
vertebrae that form the
spinal column, the bones
of the pelvis, and several
bones in the skull are
examples of irregular bones.
Long bones are relatively
long and slender. They are
located in the arm and
forearm, thigh and leg, palms,
soles, fingers, and toes. The
femur, the long bone of the
thigh, is the largest and
heaviest bone In the body.
Vertebra
Humerus
(c) Short Bones
(f) Sesamoid Bones
Short bones are
boxlike in appearance.
Examples of short
bones include the
carpal bones (wrists)
and tarsal bones
(ankles).
Sesamoid bones are usually
small, round, and flat. They
develop inside tendons and are
most often encountered near
joints at the knee, the hands, and
the feet. Few individuals have
sesamoid bones at every
possible location, but everyone
has sesamoid patellae (pa-TEL-e;
singular, patella, a small shallow
dish), or kneecaps.
Carpal
bones
Patella –