BJST Flashcards by JENA MARIE RIVERA

used as a specific marker of
osteoblast activity

Serum Osteoponin

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type 1 collagen + smaller amounts of GAGs + other proteins (osteopontin or osteocalcin- for bone formation and mineralization)

Osteoid

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primarily hydroxyapatite which give bone its hardness and serves as a repository for 99% of the calcium and 85% of the phosphorus

Minerals

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Produced rapidly (during fetal development or
fracture repair

Always abnormal in adults, but its presence is not specific for any particular disease

Woven Bone

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Supported by bony trabeculae interspersed with marrow, may be fatty (white) or hematopoietic (red)

Lamellar Bone

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Located on the surface of the osteoid matrix

Synthesize, transport, and assemble matrix and regulate mineralization

Osteoblast

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Connected by an intricate network of dendritic cytoplasmic processes through tunnels (canaliculi)

Controls calcium and phosphate levels

Mechanotransduction detects mechanical forces and translate them into myologic activity

Osteocytes

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Specialized multinucleated macrophages derived
from circulated monocytes

Responsible for bone resorption

Osteoclast

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Attaches to the bone matrix which creates sealed extracellular trench (resorption pit)

Secretion of acid and neutral proteases, (MMPs), into the pit results in dissolution of inorganic and organic
bone components

Osteoclast

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Most bones that form during embryogenesis develop from a
cartilage mold via

endochondral ossification

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Central medullary canal within the anlagen is created by
chondroblasts at approximately

8 week of gestation

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earliest bone trabeculae

Primary Spongiosa

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Dense layer of mesenchyme is directly ossified by
osteoblasts without a cartilage anlagen

Intramembranous Ossification

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Maintains chondrocyte proliferation

Growth hormone

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Acts on proliferating chondrocytes to induce
hypertrophy

Thyroid Hormone

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Coordinates chondrocyte proliferation and
differentiation with osteoblast proliferation

Indian Hedgehog

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Activates the PTH receptor to maintain
chondrocyte proliferation

PTHrP

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Activate β-catenin to promote chondrocyte
proliferation and maturation

WTN Growth Factors

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Expressed by proliferating, but not
hypertrophic, chondrocytes that is essential for
differentiation of chondrocyte precursors

SOX9

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Expressed in early hypertrophic chondrocytes
which controls terminal chondrocyte and
osteoblast differentiation

RUNX2

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Act on hypertrophic chondrocytes to inhibit
proliferation and promote differentiation

Fibroblast Growth Factor

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Chondrocyte proliferation and hypertrophy at
the growth plate

Bone Morphogenic Proteins

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Remodeling takes place at

Bone Multicellular Unit (BMU)

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Balance between bone formation and resorption is modulated by

RANK & WNT

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expressed on osteoclast precursor

Transmembrane receptor RANK

expressed on osteoblasts and marrow stromal cells

RANK ligand

“decoy” receptor made by osteoblasts; prevents interaction with RANK

Osteoprotegerin

hormones, vitamin D, inflammatory cytokines and growth factors

Systemic factors

Systemic Factors: osteoclast differentiation - increased bone turnover

PTH, IL-1 and glucocorticoids-

Systemic Factors: favor OPG expression or block osteoclast activity

Bone morphogenic proteins and sex hormones

Peak bone mass is achieved in ____ after cessation of _______

Early adulthood; skeletal growth

resorption = formation -----> decline in skeletal mass happens when

4th decade

localized disruption of the migration and condensation of the mesenchyme

Dysostoses

May occur in isolation or as part of more complex syndromes Caused by defects in mesenchymal condensation and differentiation into cartilage anlage

Dysostoses

Complete absence of a bone or entire digit

aplasia

extra bones or digits

supernumerary digit

abnormal fusion of bones

syndactyly, carniosynostosis

Complete absence of a bone or entire digit

Dysplasia

Arise from mutations in genes that control development or remodeling of the entire skeleton Implies abnormal growth, bbut it is not a precursor of neoplasia, as is the case with dysplasias of epithelial cells

Dysplasia

caused by mutations in the homeobox HOXD13 gene and are characterized by shortening of the terminal phalanges of the thumb and big toe

Brachydactyl types D & E

global disorganization of bone and/or cartilage

Dysplasia

loss of function mutation in RUNX2

Cleidocranial dysplasia

Characterized by: Patent fontanelles Delayed closure of cranial sutures Wormian bones (extra bones that occur within a cranial suture) Delayed eruption of secondary teeth Primitive clavicles Short stature

Cleidocranial Dysplasia

most common skeletal dysplasia and a major cause of dwarfism

Achondroplasia

Autosomal dominant disorder caused by gain-of-function mutations in the FGF receptor 3 (FGFR3) gene

Achondroplasia

Retarded cartilage growth results in: Shortened proximal extremities Enlarged head with bulging forehead Depression of the root of the nose despite a trunk of relatively normal length

Achondroplasia

most common lethal form of dwarfism

Thanatophoric dysplasia

Micromelic limbs, frontal bossing, relative macrocephaly, small chest cavity, and bell-shaped abdomen

Thanatophoric Dysplasia

HOXD13 Transcription factor Short, broad terminal phalanges of first digits

Brachydactyly types D and E

SOX9 Transcription factor Sex reversal, abnormal skeletal development

Camptomelic dysplasia

RUNX2 Transcription factor Abnormal clavicles, Wormian bones, supernumerary teeth

Cleidocranial dysplasia

TBX5 Transcription factor Congenital abnormalities, forelimb anomalies

Holt-Oram syndrome

LMXIB Transcription factor Hypoplastic nails, hypoplastic or aplastic patellas, dislocated radialhead, progressive nephropathy

Nail-patella syndrome

PAX3 Transcription factor Hearing loss, abnormal pigmentation, craniofacial abnormalities

Waardenburg syndrome types 1 and 3

FGFR3 Receptor Short stature, rhizomelic shortening of limbs, frontal bossing, midface deficiency

Achondroplasia

FGFR3 Receptor Disproportionately short stature, micromelia, relative macrocephaly

Hypochondroplasia

LRP5 Receptor Increased bone density, hearing loss, skeletal fragility

Osteopetrosis, autosomal dominant

RANKL Receptor - ligand Increased bone density

Osteopetrosis, infantile form

LRP5 Receptor Congenital or infantonset loss of vision, skeletal fragility

Osteoporosispseudoglioma syndrome

FGFR3 Receptor Severe limb shortening and bowing, frontal bossing, depressed nasal bridge

Thanatophoric dysplasia

COL2A1 Type II collagen Short trunk

Achondrogenesis type 2

COL10A1 Type X collagen Mildly short stature

Metaphyseal dysplasia, Schmid type

COL1A1, COL1A2 Type 1 collagen Bone fragility

Osteogenesis imperfecta types 1-4

CA2 Carbonic anhydrase Increased bone density, fragility, renal tubular acidosis

Osteopetrosis with renal tubular acidosis

CLCN7 Chloride channel Increased bone density, fragility

Osteopetrosis, late onset type 2