Bones and Skeletal Tissues
Human Anatomy & Physiology, Sixth Edition
6
Skeletal Cartilage
 Avascular & without nerves
 Vascularized perichondrium
 Three types
 Hyaline
 Elastic
 Fibrocartilage
Growth of Cartilage
 2 types of growth
 Appositional –perichondrium cells secrete matrix
 Interstitial – chondrocytes within cartilage secrete
matrix
 Calcification
 bone growth
 geriatric
Classification of Bones by Skeletal Region
 Axial skeleton
 skull, vertebral column, ribs &
sternum
 Appendicular skeleton
 limbs, pectoral girdle, & pelvic
girdle
Classification of Bones: By Shape
 Long bones
Figure 6.2a
Classification of Bones: By Shape
 Long bones
 Short bones
 Cube-shaped
carpals, tarsals, &
patella
Figure 6.2b
Classification of Bones: By Shape
 Long bones
 Short bones
 Flat bones
 sternum, &
most skull
bones
Figure 6.2c
Classification of Bones: By Shape




Long bones
Short bones
Flat bones
Irregular
bones
 Vertebrae
& pelvic
bones
Figure 6.2d
Gross Anatomical Bone Features
 Bulges, depressions, and holes that serve as:
 Attachment sites for ligaments & tendons (muscles)
 Joint surfaces
 Conduits for blood vessels and nerves
 Table 6.1
 Know It
Gross Anatomy: Structure of Long Bone
Figure 6.3
Bone Membranes
 Periosteum –
 Outer – dense, regular connective tissue
 Inner (osteogenic) - osteoblasts and osteoclasts
Endosteum
 nerves, blood, & lymphatic vessels
enter via nutrient foramina
 Secured to underlying bone
by Sharpey’s fibers
 Endosteum
 Thin membrane covering
internal surfaces of bone
Structure of Short, Irregular, and Flat Bones
 Periosteum-covered compact bone on the outside
 Endosteum-covered spongy bone (diploë) on the
inside
 no diaphysis or epiphyses
 Red marrow among
trabeculae of diploë
Bone Marrow
 Red
 Hematopoietic stem cells
 childhood
 medullary cavity & all areas of spongy bone
 adults
 diploë of flat bones, head of the femur &
humerus
 Yellow
 Adipose-like tissue
 Medullary cavity & epiphyseal spongy bone
Microscopic Structure of Bone: Compact Bone
Osteoid
Ossified
minerals
Composition of Bone: Components
 Osteocytes – mature bone cells
 Osteoblasts – bone-forming cells
 Osteoclasts – resorb or break down bone matrix
 Osteoid – unmineralized ECM of proteoglycans &
collagen
 Hydroxyapatite
 calcium phosphates
 65% of bone by mass
Bone Development
 Chondrogenesis forms cartilaginous model of
skeleton in embryos beginning in 6th week
 Osteogenesis begins by 8th week of embryonic
development
 collagen matrix
 Ossification
 Intramembranous
 develops within a fibrous membrane
 Endochondral
 replacement of hyaline cartilage model
Intramembranous Ossification
 Formation of most of the flat bones of the skull and
the clavicles
 Fibrous connective tissue membranes are formed by
mesenchymal cells
Stages of Intramembranous Ossification
Stages of Intramembranous Ossification
Endochondral Ossification
 Formation of the long bones and many irregular
bones (vertebrae)
 Chondrocytes 1st form cartilaginous model of the
bone that is replaced by osteoblasts and then
mineralized
Stages of Endochondral Ossification
Hyaline
cartilage
Primary
ossification
center
Bone
collar
1
Stages of Endochondral Ossification
Deteriorating
cartilage matrix
Hyaline
cartilage
Primary
ossification
center
Bone
collar
1
2
Stages of Endochondral Ossification
Deteriorating
cartilage matrix
Hyaline
cartilage
Primary
ossification
center
Bone
collar
Spongy
bone
formation
Blood
vessel of
periosteal
bud
1
2
3
Stages of Endochondral Ossification
Secondary
ossification
center
Deteriorating
cartilage matrix
Hyaline
cartilage
Primary
ossification
center
Bone
collar
Spongy
bone
formation
Epiphyseal
blood vessel
Medullary
cavity
Blood
vessel of
periostea
l bud
1
2
3
4
Stages of Endochondral Ossification
Secondary
ossification
center
Deteriorating
cartilage matrix
Hyaline
cartilage
Primary
ossification
center
Bone
collar
Spongy
bone
formation
Epiphyseal
blood vessel
Medullary
cavity
Articular
cartilage
Spongy
bone
Epiphyseal
plate
cartilage
Blood
vessel of
periostea
l bud
1
2
3
4
5
Figure 6.8
Functional Zones in
Long Bone Growth
Long Bone Growth and Remodeling
Figure 6.10
Appositional Growth of Bone
Central canal of osteon
Periosteal ridge
Artery
Periosteum
1 Osteoblasts beneath
periosteum secrete
bone matrix & form
ridges following
periosteal blood
vessels
Penetrating canal
2 As the ridges meet,
they form a tunnel
containing the
blood vessel
3 The periosteum
lining the tunnel is
transformed into an
endosteum and the
osteoblasts just
deep to the tunnel
endosteum secrete
bone matrix,
narrowing the canal.
4 As the osteoblasts
beneath the endosteum
form new lamellae, a new
osteon is created.
Meanwhile new
circumferential lamellae
are elaborated beneath
the periosteum and the
process is repeated,
continuing to enlarge
bone diameter.
Figure 6.11
Hormonal Regulation of Bone Growth
 During infancy and childhood, epiphyseal plate
activity is stimulated by growth hormone
 During puberty, testosterone and estrogens:
Bone Remodeling
 Osteoblasts and osteoclasts deposit and resorb bone
at periosteal and endosteal surfaces
 Requires protein, vitamins C, D, A, Ca, P, Mg, &
Mn
 Resorption
 Osteoclasts in resorption bays secrete
 enzymes that digest matrix
 acids that dissolve Ca salts
 Deposition
 Osteoblasts
 Lay down fresh osteoid matrix and induce
mineralization
Control of Remodeling
 Hormonal control loops regulate bone remodeling &
maintain Ca homeostasis in the blood
 Mechanical and gravitational forces
Hormonal Mechanism
Figure 6.12
Importance of Ionic Calcium in the Body





Transmission of nerve impulses
Muscle contraction
Blood coagulation
Secretion by glands and nerve cells
Cell division
Response to Mechanical Stress
 Wolff’s law –
 A bone grows and/or remodels in response to
mechanical stresses
 Bones are thickest where the stresses are maximal
 Long bones - midway along the shaft
 Curved bones where the curvature is greatest
 Trabeculae form along lines of stress
 Large, bony projections occur where heavy, active
muscles attach
Response to Mechanical Stress
Figure 6.13
Bone Fracture Classification
 Position of the bone ends
 nondisplaced v displaced
 Completeness of the break
 Orientation of the break to the long axis
 linear v transverse
 Whether or not the ends penetrate skin
 compound v simple
Common Types of Fractures
Common Types of Fractures
Common Types of Fractures
Stages in the Healing of a Bone Fracture
 Hematoma formation
Hematoma
1
Hematoma formation
Figure 6.14.1
Stages in the Healing of a Bone Fracture
 Fibrocartilaginous
callus formation (soft
callus)
 Granulation tissue
(fibrocartilage) grows
 Capillaries grow and
phagocytic cells clear
debris
External
callus
Internal
callus
(fibrous
tissue and
cartilage)
New
blood
vessels
Spongy
bone
trabeculae
2 Fibrocartilaginous
callus formation
Figure 6.14.2
Stages in the Healing of a Bone Fracture
 Bony callus formation
 fibrocartilage of
fibrocartilaginous callus
converts into spongy bone
 Bone callus begins 3-4
weeks after injury, and
continues until firm union
is formed 2-3 months later
Bony
callus of
spongy
bone
3 Bony callus
formation
Figure 6.14.3
Stages in the Healing of a Bone Fracture
 Bone remodeling
 Excess material on
is removed
 Compact bone is
laid down to
reconstruct shaft
walls
Healing
fracture
4 Bone remodeling
Figure 6.14.4
Homeostatic Imbalances
 Ca deficiency conditions
 Dietary or hormonal (vit D)
 Inadequate mineralization causing softened,
weakened bones
 Osteomalacia
 elderly
 Rickets
 children
Osteoporosis
 Pathology
 Condition when bone reabsorption outpaces bone deposit
 Spongy bone is most vulnerable (especially spine)
 Bones become very fragile
 Occurs most often in postmenopausal women
 Preventive measures
 Dietary Ca and vitamin D
 Increased weight-bearing exercise
 Treatments
 Hormone replacement therapy (HRT) – estrogens
 Statins
Paget’s Disease
 Excessive bone remodeling
 Initially, an excess of spongy to compact bone forms
 Later, osteoclast activity wanes, but osteoblast
activity continues resulting in filling in spongy bone
and loss of marrow
 Usually localized in the spine, pelvis, femur, and
skull
Developmental Aspects of Bones
 Mesoderm gives rise to embryonic mesenchymal
cells, which produce membranes and cartilages that
form the embryonic skeleton
 The embryonic skeleton ossifies in a predictable
timetable that allows fetal age to be easily
determined from sonograms
 At birth, most long bones are well ossified (except
for their epiphyses)
 By age 25, nearly all bones are completely ossified
 In old age, bone resorption predominates