ch. 6 bones tissues Flashcards
(66 cards)
1
Q
Cartilage
A
• Skeletal cartilage – Water lends resiliency – Contains no blood vessels or nerves – Perichondrium surrounds • Dense connective tissue girdle – Contains blood vessels for nutrient delivery – Resists outward expansion • All contain chondrocytes in lacunae and extracellular matrix
2
Q
Hyaline cartilage
A
- Provides support, flexibility, and resilience
- Collagen fibers only; most abundant type
- Articular, costal, respiratory, nasal cartilage
3
Q
Elastic cartilage
A
- Similar to hyaline cartilage, but contains elastic fibers
* External ear and epiglottis
4
Q
Fibrocartilage
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- Thick collagen fibers—has great tensile strength
* Menisci of knee; vertebral discs
5
Q
Appositional growth
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– Cells secrete matrix against external face of existing cartilage
6
Q
Interstitial growth
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– Chondrocytes divide and secrete new matrix, expanding cartilage from within
7
Q
Classification of Bones
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• 206 named bones in skeleton • Divided into two groups – Axial skeleton • Long axis of body • Skull, vertebral column, rib cage – Appendicular skeleton • Bones of upper and lower limbs • Girdles attaching limbs to axial skeleton
8
Q
Classification of Bones by Shape
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• Long bones • Short bones • Flat bones • Irregular bones Classification of Bones by Shape
9
Q
Long bones
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– Longer than they are wide
– Limb, wrist, ankle bones
10
Q
Short bones
A
– Cube-shaped bones (in wrist and ankle)
– Sesamoid bones (within tendons, e.g., Patella)
– Vary in size and number in different individuals
11
Q
Flat bones
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– Thin, flat, slightly curved
– Sternum, scapulae, ribs, most skull bones
12
Q
Irregular bones
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– Complicated shapes
– Vertebrae, coxal bones
13
Q
Seven important functions of bone
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– Support – Protection – Movement – Mineral and growth factor storage – Blood cell formation – Triglyceride (fat) storage – Hormone production
14
Q
Bones
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• Are organs – Contain different types of tissues • Bone (osseous) tissue, nervous tissue, cartilage, fibrous connective tissue, muscle and epithelial cells in its blood vessels • Three levels of structure – Gross anatomy – Microscopic – Chemical
15
Q
Gross Anatomy
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• Bone textures – Compact and spongy bone • Compact – Dense outer layer; smooth and solid • Spongy (cancellous or trabecular) – Honeycomb of flat pieces of bone deep to compact called trabeculae
16
Q
Structure of Short, Irregular, and Flat Bones
A
• Thin plates of spongy bone covered by compact bone
• Plates sandwiched between connective tissue membranes
– Periosteum (outer layer) and endosteum
• No shaft or epiphyses
• Bone marrow throughout spongy bone; no marrow cavity
• Hyaline cartilage covers articular surfaces
17
Q
Structure of Typical Long Bone
A
• Diaphysis
– Tubular shaft forms long axis
– Compact bone surrounding medullary cavity
• Epiphyses
– Bone ends
– External compact bone; internal spongy bone
– Articular cartilage covers articular surfaces
– Between is epiphyseal line
• Remnant of childhood bone growth at epiphyseal plate
18
Q
Membranes: Periosteum
A
• White, double-layered membrane
• Covers external surfaces except joint surfaces
• Outer fibrous layer of dense irregular connective tissue
– Sharpey’s fibers secure to bone matrix
• Osteogenic layer abuts bone
– Contains primitive stem cells – osteogenic cells
• Many nerve fibers and blood vessels
• Anchoring points for tendons and ligaments
Membranes: Endosteum
• Delicate connective tissue membrane covering internal bone surface
• Covers trabeculae of spongy bone
• Lines canals that pass through compact bone
• Contains osteogenic cells that can differentiate into other bone cells
19
Q
Hematopoietic Tissue in Bones
A
• Red marrow
– Found within trabecular cavities of spongy bone and diploë of flat bones (e.g., Sternum)
– In medullary cavities and spongy bone of newborns
– Adult long bones have little red marrow
• Heads of femur and humerus only
– Red marrow in diploë and some irregular bones is most active
– Yellow marrow can convert to red, if necessary
20
Q
Bone Markings
A
- Sites of muscle, ligament, and tendon attachment on external surfaces
- Joint surfaces
- Conduits for blood vessels and nerves
- Projections
- Depressions
- Openings
21
Q
Bone Markings
A
• Projections
– Most indicate stresses created by muscle pull or joint modifications
• Depressions and openings
• Usually allow nerves and blood vessels to pass
22
Q
Microscopic Anatomy of Bone: Cells of Bone Tissue
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• Five major cell types • Each specialized form of same basic cell type – Osteogenic cells – Osteoblasts – Osteocytes – Bone lining cells – Osteoclasts
23
Q
Osteogenic Cells
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• Also called osteoprogenitor cells
– Mitotically active stem cells in periosteum and endosteum
– When stimulated differentiate into osteoblasts or bone lining cells
• Some persist as osteogenic cells
24
Q
Osteoblasts
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• Bone-forming cells
• Secrete unmineralized bone matrix or osteoid
– Includes collagen and calcium-binding proteins
• Collagen = 90% of bone protein
• Actively mitotic
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Osteocytes
• Mature bone cells in lacunae
• Monitor and maintain bone matrix
• Act as stress or strain sensors
– Respond to and communicate mechanical stimuli to osteoblasts and osteoclasts (cells that destroy bone) so bone remodeling can occur
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Bone Lining Cells
* Flat cells on bone surfaces believed to help maintain matrix
* On external bone surface called periosteal cells
* Lining internal surfaces called endosteal cells
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Osteoclasts
• Derived from hematopoietic stem cells that become macrophages
• Giant, multinucleate cells for bone resorption
• When active rest in resorption bay and have ruffled border
– Ruffled border increases surface area for enzyme degradation of bone and seals off area from surrounding matrix
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Compact Bone
• Also called lamellar bone
• Osteon or haversian system
– Structural unit of compact bone
– Elongated cylinder parallel to long axis of bone
– Hollow tubes of bone matrix called lamellae
• Collagen fibers in adjacent rings run in different directions
– Withstands stress – resist twisting
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Lamellae
– Incomplete lamellae not part of complete osteon
– Fill gaps between forming osteons
– Remnants of osteons cut by bone remodeling
• Circumferential lamellae
– Just deep to periosteum
– Superficial to endosteum
– Extend around entire surface of diaphysis
– Resist twisting of long bone
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Spongy Bone
• Appears poorly organized
• Trabeculae
– Align along lines of stress to help resist it
– No osteons
– Contain irregularly arranged lamellae and osteocytes interconnected by canaliculi
– Capillaries in endosteum supply nutrients
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Chemical Composition of Bone: Organic Components
• Includes cells and osteoid
– Osteogenic cells, osteoblasts, osteocytes, bone- lining cells, and osteoclasts
– Osteoid—1/3 of organic bone matrix secreted by osteoblasts
• Made of ground substance (proteoglycans and glycoproteins)
• Collagen fibers
• Contributes to structure; provides tensile strength and flexibility
• Resilience of bone due to sacrificial bonds in or between collagen molecules
– Stretch and break easily on impact to dissipate energy and prevent fracture
– If no addition trauma, bonds re-form
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Chemical Composition of Bone:
| Inorganic Components
• Hydroxyapatites (mineral salts)
– 65% of bone by mass
– Mainly of tiny calcium phosphate crystals in and around collagen fibers
– Responsible for hardness and resistance to compression
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Bone
• Half as strong as steel in resisting compression
• As strong as steel in resisting tension
• Last long after death because of mineral composition
– Reveal information about ancient people
– Can display growth arrest lines
• Horizontal lines on bones
• Proof of illness - when bones stop growing so nutrients can help fight disease
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Bone Development
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• Ossification (osteogenesis)
– Process of bone tissue formation
– Formation of bony skeleton
• Begins in 2nd month of development
– Postnatal bone growth
• Until early adulthood
– Bone remodeling and repair
• Lifelong
Two Types of Ossification
• Endochondral ossification
– Bone forms by replacing hyaline cartilage
– Bones called cartilage (endochondral) bones
– Forms most of skeleton
• Intramembranous ossification
– Bone develops from fibrous membrane
– Bones called membrane bones
– Forms flat bones, e.g. clavicles and cranial bones
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Endochondral Ossification
• Forms most all bones inferior to base of skull
– Except clavicles
• Begins late in 2nd month of development
• Uses hyaline cartilage models
• Requires breakdown of hyaline cartilage prior to ossification
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Intramembranous Ossification
* Forms frontal, parietal, occipital, temporal bones, and clavicles
* Begins within fibrous connective tissue membranes formed by mesenchymal cells
* Ossification centers appear
* Osteoid is secreted
* Woven bone and periosteum form
* Lamellar bone replaces woven bone & red marrow appears
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Postnatal Bone Growth
• Interstitial (longitudinal) growth
– Increase in length of long bones
• Appositional growth
– Increase in bone thickness
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Growth in Length of Long Bones
• Requires presence of epiphyseal cartilage
• Epiphyseal plate maintains constant thickness
– Rate of cartilage growth on one side balanced by bone replacement on other
• Concurrent remodeling of epiphyseal ends to maintain proportion
• Result of five zones within cartilage
– Resting (quiescent) zone
– Proliferation (growth) zone
– Hypertrophic zone
– Calcification zone
– Ossification (osteogenic) zone
• Resting (quiescent) zone
– Cartilage on epiphyseal side of epiphyseal plate
– Relatively inactive
• Proliferation (growth) zone
• Calcification zone
– Surrounding cartilage matrix calcifies, chondrocytes die and deteriorate
• Ossification zone
– Chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction
– Spicules eroded by osteoclasts
– Covered with new bone by osteoblasts
– Ultimately replaced with spongy bone
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– Cartilage on diaphysis side of epiphyseal plate • Near end of adolescence chondroblasts divide less often
• Epiphyseal plate thins then is replaced by bone
• Epiphyseal plate closure
– Bone lengthening ceases
• Requires presence of cartilage
– Bone of epiphysis and diaphysis fuses
– Females – about 18 years
– Males – about 21 years
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– Rapidly divide pushing epiphysis away from diaphysis lengthening
• Hypertrophic zone
– Older chondrocytes closer to diaphysis and their lacunae enlarge and erode interconnecting spaces
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Growth in Width
• Allows lengthening bone to widen
• Occurs throughout life
• Osteoblasts beneath periosteum secrete bone matrix on external bone
• Osteoclasts remove bone on endosteal surface
• Usually more building up than breaking down
– Thicker, stronger bone but not too heavy
40
Hormonal Regulation of Bone Growth
• Growth hormone
– Most important in stimulating epiphyseal plate activity in infancy and childhood
• Thyroid hormone
– Modulates activity of growth hormone
– Ensures proper proportions
• Testosterone (males) and estrogens (females) at puberty
– Promote adolescent growth spurts
– End growth by inducing epiphyseal plate closure
• Excesses or deficits of any cause abnormal skeletal growth
41
Bone Homeostasis
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• Recycle 5-7% of bone mass each week
– Spongy bone replaced ~ every 3-4 years
– Compact bone replaced ~ every 10 years
• Older bone becomes more brittle
– Calcium salts crystallize
– Fractures more easily
• Consists of bone remodeling and bone repair
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42
Bone Remodeling
• Consists of both bone deposit and bone resorption
• Occurs at surfaces of both periosteum and endosteum
• Remodeling units
– Adjacent osteoblasts and osteoclasts
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Bone Deposit
• Evidence of new matrix deposit by osteoblasts
– Osteoid seam
• Unmineralized band of bone matrix
– Calcification front
• Abrupt transition zone between osteoid seam and older mineralized bone
• Trigger not confirmed
– Mechanical signals involved
– Endosteal cavity concentrations of calcium and phosphate ions for hydroxyapatite formation
– Matrix proteins bind and concentrate calcium
– Enzyme alkaline phosphatase for mineralization
44
Bone Resorption
• Is function of osteoclasts
– Dig depressions or grooves as break down matrix
– Secrete lysosomal enzymes that digest matrix and protons (H+)
– Acidity converts calcium salts to soluble forms
• Osteoclasts also
– Phagocytize demineralized matrix and dead osteocytes
• Transcytosis allow release into interstitial fluid and then into blood
– Once resorption complete, osteoclasts undergo apoptosis
• Osteoclast activation involves PTH and T cell-secreted proteins
45
Control of Remodeling
• Occurs continuously but regulated by genetic factors and two control loops
– Negative feedback hormonal loop for Ca2+ homeostasis
• Controls blood Ca2+ levels; Not bone integrity
– Responses to mechanical and gravitational forces
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Importance of Calcium
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• Functions in
– Nerve impulse transmission
– Muscle contraction
– Blood coagulation
– Secretion by glands and nerve cells
– Cell division
• 1200 – 1400 grams of calcium in body
– 99% as bone minerals
– Amount in blood tightly regulated (9-11 mg/dl)
– Intestinal absorption requires Vitamin D metabolites
– Dietary intake required
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Hormonal Control of Blood Ca2+
• Parathyroid hormone (PTH)
– Produced by parathyroid glands
– Removes calcium from bone regardless of bone integrity• Calcitonin may be involved
– Produced by parafollicular cells of thyroid gland
– In high doses lowers blood calcium levels temporarily
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Calcium Homeostasis
• Even minute changes in blood calcium dangerous
– Severe neuromuscular problems
• Hyperexcitability (levels too low)
• Nonresponsiveness (levels too high)
– Hypercalcemia
• Sustained high blood calcium levels
• Deposits of calcium salts in blood vessels, kidneys can interfere with function
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Other Hormones Affecting Bone Density
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• Leptin
– Hormone released by adipose tissue
– Role in bone density regulation
• Inhibits osteoblasts in animals
• Serotonin
– Neurotransmitter regulating mood and sleep
– Most made in gut
– Secreted into blood after eating
• Interferes with osteoblast activity
• Serotonin reuptake inhibitors
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50
Response to Mechanical Stress
• Bones reflect stresses they encounter
– Long bones thickest midway along diaphysis where bending stresses greatest
• Bones stressed when weight bears on them or muscles pull on them
– Usually off center so tends to bend bones
– Bending compresses on one side; stretches on other
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Results of Mechanical Stressors:
| Wolff's Law
• Bones grow or remodel in response to demands placed on it
• Explains
– Handedness (right or left handed) results in thicker and stronger bone of that upper limb
– Curved bones thickest where most likely to buckle
– Trabeculae form trusses along lines of stress
– Large, bony projections occur where heavy, active muscles attach
– Bones of fetus and bedridden featureless
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How Mechanical Stress Causes Remodeling
• Electrical signals produced by deforming bone may cause remodeling
– Compressed and stretched regions oppositely charged
• Fluid flows within canaliculi appear to provide remodeling stimulus
Results of Hormonal and Mechanical Influences
• Hormonal controls determine whether and when remodeling occurs to changing blood calcium levels
• Mechanical stress determines where remodeling occurs
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Bone Repair
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• Fractures
– Breaks
– Youth
• Most result from trauma
– Old age
• Most result of weakness from bone thinning
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Fracture Classification
• Three "either/or" fracture classifications
– Position of bone ends after fracture
• Nondisplaced—ends retain normal position
• Displaced—ends out of normal alignment
– Completeness of break
• Complete—broken all the way through
• Incomplete—not broken all the way through
– Whether skin is penetrated
• Open (compound) - skin is penetrated
• Closed (simple) – skin is not penetrated
• Also described by location of fracture
• External appearance
• Nature of break
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Fracture Treatment and Repair
• Treatment
– Reduction
• Realignment of broken bone ends
• Closed reduction – physician manipulates to correct position
• Open reduction – surgical pins or wires secure ends
– Immobilization by cast or traction for healing
• Depends on break severity, bone broken, and age of patient
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Stages of Bone Repair: HEMATOMA Forms
* Torn blood vessels hemorrhage
* Clot (hematoma) forms
* Site swollen, painful, and inflamed
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Stages of Bone Repair:
| Fibrocartilaginous Callus Forms
• Capillaries grow into hematoma
• Phagocytic cells clear debris
• Fibroblasts secrete collagen fibers to span break and connect broken ends
• Fibroblasts, cartilage, and osteogenic cells begin reconstruction of bone
– Create cartilage matrix of repair tissue
– Osteoblasts form spongy bone within matrix• Mass of repair tissue called fibrocartilaginous callus
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Stages of Bone Repair:
| Bony Callus Forms
* Within one week new trabeculae appear in fibrocartilaginous callus
* Callus converted to bony (hard) callus of spongy bone
* ~2 months later firm union forms
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Stages of Bone Repair:
| Bone Remodeling Occurs
* Begins during body callus formation
* Continues for several months
* Excess material on diaphysis exterior and within medullary cavity removed
* Compact bone laid down to reconstruct shaft walls
* Final structure resembles original because responds to same mechanical stressors
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Homeostatic Imbalances
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• Osteomalacia
– Bones poorly mineralized
– Calcium salts not adequate
– Soft, weak bones
– Pain upon bearing weight
• Rickets (osteomalacia of children)
– Bowed legs and other bone deformities
– Bones ends enlarged and abnormally long
– Cause: Vitamin D deficiency or insufficient dietary calcium
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Osteoporosis
– Group of diseases
– Bone resorption outpaces deposit
– Spongy bone of spine and neck of femur most susceptible
• Vertebral and hip fractures common
Risk Factors for Osteoporosis
• Risk factors
– Most often aged, postmenopausal women
• 30% 60 – 70 years of age; 70% by age 80
• 30% caucasian women will fracture bone because of it
– Men to lesser degree
– Sex hormones maintain normal bone health and density
• As secretion wanes with age osteoporosis can develop
Additional Risk Factors for Osteoporosis
• Petite body form
• Insufficient exercise to stress bones
• Diet poor in calcium and protein
• Smoking
• Hormone-related conditions
– Hyperthyroidism
– Low blood levels of thyroid-stimulating hormone
– Diabetes mellitus
• Immobility
• Males with prostate cancer taking androgen-suppressing drugs
Treating Osteoporosis
• Traditional treatments
– Calcium
– Vitamin D supplements
– Weight-bearing exercise
– Hormone replacement therapy
• Slows bone loss but does not reverse it
• Controversial due to increased risk of heart attack, stroke, and breast cancer
• Some take estrogenic compounds in soy as substitute
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New Drugs for Osteoporosis Treatment
• Bisphosphonates
– Decrease osteoclast activity and number
– Partially reverse in spine
• Selective estrogen receptor modulators
– Mimic estrogen without targeting breast and uterus
• Statins
– Though for lowering cholesterol also increase bone mineral density
• Denosumab
– Monoclonal antibody
– Reduces fractures in men with prostate cancer
– Improves bone density in elderly
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Preventing Osteoporosis
• Plenty of calcium in diet in early adulthood
• Reduce carbonated beverage and alcohol consumption
– Leaches minerals from bone so decreases bone density
• Plenty of weight-bearing exercise
– Increases bone mass above normal for buffer against age-related bone loss
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Paget's Disease
• Excessive and haphazard bone deposit and resorption
– Bone made fast and poorly – called pagetic bone
• Very high ratio of spongy to compact bone and reduced mineralization
– Usually in spine, pelvis, femur, and skull
• Rarely occurs before age 40
• Cause unknown - possibly viral
• Treatment includes calcitonin and biphosphonates
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Developmental Aspects of Bones
* Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms
* Most long bones begin ossifying by 8 weeks
* Primary ossification centers by 12 weeks
* At birth, most long bones well ossified (except epiphyses)
* At age 25 ~ all bones completely ossified and skeletal growth ceases
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Age-related Changes in Bone
• Children and adolescents
– Bone formation exceeds resorption
• Young adults
– Both in balance; males greater mass
• Bone density changes over lifetime largely determined by genetics
– Gene for Vitamin D's cellular docking determines mass early in life and osteoporosis risk as age
• Bone mass, mineralization, and healing ability decrease with age beginning in 4th decade
– Except bones of skull
– Bone loss greater in whites and in females
– Electrical stimulation; Daily ultrasound treatments hasten repair
