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10/18/14 Bone Development 6 •  Osteogenesis (_____________________) —
bone Dssue formaDon •  Stages –  Bone formaDon—begins in the 2nd month of development –  Postnatal bone growth—unDl early adulthood –  Bone remodeling and repair—________________ Bones and Skeletal Tissues: Part B Two Types of OssificaDon Mesenchymal
cell
Collagen
fiber
Ossification
center
1.  ___________________________ ossificaDon –  Membrane bone develops from fibrous membrane –  Forms flat bones, e.g. clavicles and cranial bones 2.  ___________________________ ossificaDon –  CarDlage (endochondral) bone forms by replacing hyaline carDlage –  Forms most of the rest of the skeleton Osteoid
Osteoblast
Ossification centers appear in the fibrous
connective tissue membrane.
• Selected centrally located mesenchymal cells cluster
and differentiate into osteoblasts, forming an
ossification center.
1
Figure 6.8, (1 of 4)
1 10/18/14 Osteoblast
Osteoid
Osteocyte
Newly calcified
bone matrix
2 Bone matrix (osteoid) is secreted within the
fibrous membrane and calcifies.
• Osteoblasts begin to secrete osteoid, which is calcified
within a few days.
• Trapped osteoblasts become osteocytes.
Mesenchyme
condensing
to form the
periosteum
Trabeculae of
woven bone
Blood vessel
3 Woven bone and periosteum form.
• Accumulating osteoid is laid down between embryonic
blood vessels in a random manner. The result is a network
(instead of lamellae) of trabeculae called woven bone.
• Vascularized mesenchyme condenses on the external face
of the woven bone and becomes the periosteum.
Figure 6.8, (2 of 4)
Figure 6.8, (3 of 4)
Endochondral OssificaDon Fibrous
periosteum
Osteoblast
Plate of
compact bone
Diploë (spongy
bone) cavities
contain red
marrow
•  Uses __________________ carDlage models •  Requires breakdown of hyaline carDlage prior to ossificaDon 4 Lamellar bone replaces woven bone, just deep to
the periosteum. Red marrow appears.
• Trabeculae just deep to the periosteum thicken, and are later
replaced with mature lamellar bone, forming compact bone
plates.
• Spongy bone (diploë), consisting of distinct trabeculae, persists internally and its vascular tissue becomes red marrow.
Figure 6.8, (4 of 4)
2 10/18/14 Month 3
Week 9
Birth
Childhood to
adolescence
Articular
cartilage
Secondary
ossification
center
Epiphyseal
blood vessel
Area of
deteriorating
cartilage matrix
Hyaline
cartilage
Spongy
bone
formation
Bone
collar
Primary
ossification
center
Spongy
bone
•  _________________ growth: –  ↑ length of long bones Epiphyseal
plate
cartilage
•  _________________ growth: Medullary
cavity
–  ↑ thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces Blood
vessel of
periosteal
bud
1 Bone collar
2 Cartilage in the
forms around
center of the
hyaline cartilage diaphysis calcifies
model.
and then develops
cavities.
3 The periosteal
bud inavades the
internal cavities
and spongy bone
begins to form.
4 The diaphysis elongates
and a medullary cavity
forms as ossification
continues. Secondary
ossification centers appear
in the epiphyses in
preparation for stage 5.
Postnatal Bone Growth 5 The epiphyses
ossify. When
completed, hyaline
cartilage remains only
in the epiphyseal
plates and articular
cartilages.
Figure 6.9
Growth in Length of Long Bones Resting zone
•  Epiphyseal plate carDlage organizes into four important _______________ __________: –  ProliferaDon (growth) –  Hypertrophic –  CalcificaDon –  OssificaDon (osteogenic) 1 Proliferation zone
Cartilage cells undergo
mitosis.
2 Hypertrophic zone
Older cartilage cells
enlarge.
Calcified cartilage
spicule
Osteoblast depositing
bone matrix
Osseous tissue
(bone) covering
cartilage spicules
3 Calcification zone
Matrix becomes calcified;
cartilage cells die; matrix
begins deteriorating.
4 Ossification zone
New bone formation is
occurring.
Figure 6.10
3 10/18/14 Hormonal RegulaDon of Bone Growth •  Growth hormone sDmulates ________________ ___________ acDvity •  Thyroid hormone modulates acDvity of growth hormone •  Testosterone and estrogens (at ________________) –  Promote adolescent growth spurts –  End growth by inducing epiphyseal plate closure Bone growth
Cartilage
grows here.
Cartilage
is replaced
by bone here.
Cartilage
grows here.
Cartilage
is replaced
by bone here.
Bone remodeling
Articular cartilage
Epiphyseal plate
Bone is
resorbed here.
Bone is added
by appositional
growth here.
Bone is
resorbed here.
Figure 6.11
Bone Deposit •  Occurs where bone is ________________ or added strength is needed •  Requires a diet rich in protein; vitamins C, D, and A; calcium; phosphorus; magnesium; and manganese Bone Deposit •  Sites of new matrix deposit are revealed by the –  _________________________ •  Unmineralized band of matrix –  _________________________ •  The abrupt transiDon zone between the osteoid seam and the older mineralized bone 4 10/18/14 Bone ResorpDon •  _________________________ secrete –  Lysosomal enzymes (digest organic matrix) –  Acids (convert calcium salts into soluble forms) •  Dissolved matrix is transcytosed across osteoclast, enters intersDDal fluid and then _________________ Hormonal Control of Blood Ca2+ •  _________________ is necessary for –  Transmission of nerve impulses –  _________________ contracDon –  _________________ coagulaDon –  SecreDon by glands and _________________ –  Cell division Control of Remodeling •  What controls conDnual _________________ of bone? –  Hormonal mechanisms that maintain calcium homeostasis in the blood –  Mechanical and _________________ forces Hormonal Control of Blood Ca2+ •  Primarily controlled by parathyroid hormone (PTH) ↓ Blood Ca2+ levels ↓ Parathyroid glands release PTH ↓ PTH sDmulates osteoclasts to degrade bone matrix and release Ca2+ ↓ ↑ Blood Ca2+ levels 5 10/18/14 Hormonal Control of Blood Ca2+ Calcium homeostasis of blood: 9–11 mg/100 ml
BALANCE
BALANCE
Stimulus
Falling blood
Ca2+ levels
Thyroid
gland
Osteoclasts
degrade bone
matrix and
release Ca2+
into blood.
Parathyroid
glands
PTH
Parathyroid
glands release
parathyroid
hormone (PTH).
•  May be affected to a lesser extent by calcitonin ↑ Blood Ca2+ levels ↓ Parafollicular cells of thyroid release calcitonin ↓ Osteoblasts deposit calcium salts ↓ ↓ Blood Ca2+ levels •  LepDn has also been shown to influence bone density by inhibiDng _________________ Figure 6.12
Load here (body weight)
Response to Mechanical Stress •  _________________: A bone grows or remodels in response to forces or demands placed upon it •  ObservaDons supporDng Wolff’s law: –  _________________ (right or lec handed) results in bone of one upper limb being thicker and stronger –  Curved bones are thickest where they are most likely to buckle –  Trabeculae form along _________________ –  Large, bony projecDons occur where heavy, acDve _________________ aeach Head of
femur
Tension
here
Compression
here
Point of
no stress
Figure 6.13
6 10/18/14 • 
ClassificaDon of Bone Fractures ClassificaDon of Bone Fractures Bone _________________ may be classified by four “either/or” classificaDons: 3.  _________________ of the break to the long axis of the bone: •  Linear—parallel to long axis of the bone •  Transverse—perpendicular to long axis of the bone 4.  Whether or not the bone ends _________________ the skin: •  _________________ (open)—bone ends penetrate the skin •  _________________ (closed)—bone ends do not penetrate the skin 1.  PosiDon of bone ends acer fracture: •  Nondisplaced—ends retain normal posiDon •  Displaced—ends out of normal alignment 2.  Completeness of the break •  _________________—broken all the way through •  _________________—not broken all the way through Common Types of Fractures •  All fractures can be described in terms of –  _________________ –  _________________ –  _________________ Table 6.2
7 10/18/14 Table 6.2
Stages in the Healing of a Bone Fracture Table 6.2
Hematoma
1.  _________________ forms –  Torn blood vessels hemorrhage –  Clot (hematoma) forms –  Site becomes swollen, painful, and _________________ 1 A hematoma forms.
Figure 6.15, step 1
8 10/18/14 Stages in the Healing of a Bone Fracture External
callus
2.  _________________ callus forms –  PhagocyDc cells clear debris –  Osteoblasts begin forming spongy bone within 1 week –  Fibroblasts secrete _________________ to connect bone ends –  Mass of repair Dssue now called fibrocarDlaginous callus Internal
callus
(fibrous
tissue and
cartilage)
New
blood
vessels
Spongy
bone
trabecula
2 Fibrocartilaginous
callus forms.
Figure 6.15, step 2
Stages in the Healing of a Bone Fracture 3.  ________ _________formaDon –  New trabeculae form a bony (hard) callus –  Bony callus formaDon conDnues unDl firm union is formed in ~2 months Bony
callus of
spongy
bone
3 Bony callus forms.
Figure 6.15, step 3
9 10/18/14 Stages in the Healing of a Bone Fracture 4.  Bone _________________ –  In response to mechanical stressors over several months –  Final structure resembles _________________ Healed
fracture
4 Bone remodeling
occurs.
Figure 6.15, step 4
HomeostaDc Imbalances •  _________________ and rickets Hematoma
Internal
callus
(fibrous
tissue and
cartilage)
External
callus
New
blood
vessels
Bony
callus of
spongy
bone
Healed
fracture
Spongy
bone
trabecula
1 A hematoma forms. 2 Fibrocartilaginous
3 Bony callus forms.
callus forms.
4 Bone
remodeling
occurs.
–  Calcium salts not deposited –  Rickets (childhood disease) causes bowed legs and other bone deformiDes –  Cause: _________________deficiency or insufficient dietary calcium Figure 6.15
10 10/18/14 HomeostaDc Imbalances •  _________________ –  Loss of bone mass—bone resorpDon outpaces deposit –  Spongy bone of spine and neck of femur become most suscepDble to fracture –  _________________ •  Lack of estrogen, calcium or vitamin D; peDte body form; immobility; low levels of TSH; diabetes mellitus Figure 6.16
Osteoporosis: Treatment and PrevenDon •  Calcium, vitamin D, and fluoride supplements •  ↑ Weight-­‐bearing exercise throughout life •  Hormone (_________________) replacement therapy (HRT) slows bone loss •  Some _________________ (Fosamax, SERMs, staDns) increase bone mineral density Paget’s Disease •  Excessive and haphazard bone formaDon and breakdown, usually in spine, pelvis, femur, or skull •  PageDc bone has very high raDo of _________________ to _________________ bone and reduced mineralizaDon •  Unknown cause (possibly ______________) •  _________________ includes calcitonin and biphosphonates 11 10/18/14 Developmental Aspects of Bones Parietal bone
Occipital bone
•  _________________ skeleton ossifies predictably so fetal age easily determined from X rays or sonograms •  At birth, most ___________ __________ are well ossified (except _________________) Mandible
Frontal bone
of skull
Clavicle
Scapula
Radius
Ulna
Ribs
Humerus
Vertebra
Ilium
Tibia
Femur
Figure 6.17
Developmental Aspects of Bones •  Nearly all bones completely _________________ by age 25 •  Bone mass decreases with age beginning in 4th decade •  Rate of loss determined by _________________ and environmental factors •  In old age, bone _________________ predominates 12