bone&development · 10/18/14 2 figure 6.8, (2 of 4) osteoid osteocyte newly calcified bone...
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Bones and Skeletal Tissues: Part B
Bone Development
• Osteogenesis (_____________________) —bone Dssue formaDon
• Stages – Bone formaDon—begins in the 2nd month of development
– Postnatal bone growth—unDl early adulthood – Bone remodeling and repair—________________
Two Types of OssificaDon
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
Figure 6.8, (1 of 4)
Mesenchymal cell Collagen fiber Ossification center
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.
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Figure 6.8, (2 of 4)
Osteoid
Osteocyte
Newly calcified bone matrix
Osteoblast
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.
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Figure 6.8, (3 of 4)
Mesenchyme condensing to form the periosteum
Blood vessel
Trabeculae of woven bone
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.
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Figure 6.8, (4 of 4)
Fibrous periosteum
Osteoblast
Plate of compact bone
Diploë (spongy bone) cavities contain red marrow
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, per- sists internally and its vascular tissue becomes red marrow.
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Endochondral OssificaDon
• Uses __________________ carDlage models • Requires breakdown of hyaline carDlage prior to ossificaDon
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Figure 6.9
Bone collar forms around hyaline cartilage model.
Cartilage in the center of the diaphysis calcifies and then develops cavities.
The periosteal bud inavades the internal cavities and spongy bone begins to form.
The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5.
The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.
Hyaline cartilage
Area of deteriorating cartilage matrix
Epiphyseal blood vessel
Spongy bone formation
Epiphyseal plate cartilage
Secondary ossification center
Blood vessel of periosteal bud
Medullary cavity
Articular cartilage
Childhood to adolescence
Birth Week 9 Month 3
Spongy bone
Bone collar Primary ossification center
1 2 3 4 5
Postnatal Bone Growth
• _________________ growth: – ↑ length of long bones
• _________________ growth: – ↑ thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces
Growth in Length of Long Bones
• Epiphyseal plate carDlage organizes into four important _______________ __________: – ProliferaDon (growth) – Hypertrophic – CalcificaDon – OssificaDon (osteogenic)
Figure 6.10
Calcified cartilage spicule
Osseous tissue (bone) covering cartilage spicules
Resting zone
Osteoblast depositing bone matrix
Proliferation zone Cartilage cells undergo mitosis.
Hypertrophic zone Older cartilage cells enlarge.
Ossification zone New bone formation is occurring.
Calcification zone Matrix becomes calcified; cartilage cells die; matrix begins deteriorating.
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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
Figure 6.11
Bone growth Bone remodeling
Articular cartilage
Epiphyseal plate
Cartilage grows here.
Cartilage is replaced by bone here. Cartilage grows here.
Bone is resorbed here.
Bone is resorbed here.
Bone is added by appositional growth here. Cartilage
is replaced by bone here.
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
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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 _________________
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+
• _________________ is necessary for – Transmission of nerve impulses – _________________ contracDon – _________________ coagulaDon – SecreDon by glands and _________________ – Cell division
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
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Figure 6.12
Osteoclasts degrade bone matrix and release Ca2+ into blood.
Parathyroid glands
Thyroid gland
Parathyroid glands release parathyroid hormone (PTH).
Stimulus Falling blood Ca2+ levels
PTH
Calcium homeostasis of blood: 9–11 mg/100 ml BALANCE BALANCE
Hormonal Control of Blood Ca2+
• 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 _________________
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
Figure 6.13
Load here (body weight)
Head of femur
Compression here
Point of no stress
Tension here
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ClassificaDon of Bone Fractures
• Bone _________________ may be classified by four “either/or” classificaDons:
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
ClassificaDon of Bone Fractures 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
Common Types of Fractures
• All fractures can be described in terms of – _________________ – _________________ – _________________
Table 6.2
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Table 6.2 Table 6.2
Stages in the Healing of a Bone Fracture
1. _________________ forms – Torn blood vessels hemorrhage – Clot (hematoma) forms – Site becomes swollen, painful, and
_________________
Figure 6.15, step 1
A hematoma forms. 1
Hematoma
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Stages in the Healing of a Bone Fracture
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
Figure 6.15, step 2
Fibrocartilaginous callus forms. 2
External callus
New blood vessels
Spongy bone trabecula
Internal callus (fibrous tissue and cartilage)
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
Figure 6.15, step 3
Bony callus forms. 3
Bony callus of spongy bone
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Stages in the Healing of a Bone Fracture
4. Bone _________________ – In response to mechanical stressors over several
months – Final structure resembles _________________
Figure 6.15, step 4
Bone remodeling occurs. 4
Healed fracture
Figure 6.15
Hematoma External callus
Bony callus of spongy bone Healed fracture
New blood vessels
Spongy bone trabecula
Internal callus (fibrous tissue and cartilage)
A hematoma forms. Fibrocartilaginous callus forms.
Bony callus forms. Bone remodeling occurs.
1 2 3 4
HomeostaDc Imbalances
• _________________ and rickets – Calcium salts not deposited – Rickets (childhood disease) causes bowed legs and other bone deformiDes
– Cause: _________________deficiency or insufficient dietary calcium
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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
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Developmental Aspects of Bones
• _________________ skeleton ossifies predictably so fetal age easily determined from X rays or sonograms
• At birth, most ___________ __________ are well ossified (except _________________)
Figure 6.17
Parietal bone
Radius Ulna
Humerus
Femur
Occipital bone
Clavicle Scapula
Ribs
Vertebra Ilium
Tibia
Frontal bone of skull Mandible
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