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30 Cards in this Set

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osteogenic cells

•stemcells–Multiply continuously to makeosteoblasts


•bone-formingcells–Make soft organic matter of matrixwhich thenhardens by mineral deposition


•bone-dissolvingcells found on the bone surface–Unusually large cells formed fromthe fusion of several stem cells


•formerosteoblasts that have become trapped in the matrix they have deposited–Whenstressed, produce biochemical signals that regulate bone remodeling

What constitutes the matrix of bone?

•–Organic matter (1/3 of matrix)—madeby osteoblasts•Collagen, carbohydrate–proteincomplexes•Flexibility

•–Inorganic matter (2/3 of matrix) •85% hydroxyapatite (crystallizedcalcium phosphate salt)•10% calcium carbonate•Other minerals (fluoride, sodium,potassium, magnesium)•Strength

Organic matter in the matrix of the bone is made by....


What are the bone types?

•Compact (cortical)—looks compact,more dense•Spongy (trabecular/cancellous)—looks “spongy”

What is compact bone made of?

•Osteon = basic structural unit of compactbone•–Concentric lamellae (layers ofmatrix and cells)–Cylinderof tissue around a central canal•BVsand nerves

Spongy bone consists of...

–Thinplates of bone called trabeculae –Spacesfilled with redbone marrow

Advantage of spongy bone over compact bone

Lighter but still strong

How is spongy bone related to mechanical stress?

Lamallae line/form at the line of stress for strengthening purposes

Where is bone marrow found?

•Marrow cavity and spaces betweentrabeculae

Types of Bone Marrow

•Red (myeloid tissue)–Hemopoietic—producesblood cells–Morein children–Adults—skull,vertebrae,ribs,sternum,part of pelvicgirdle,and proximalheads of humerusand femur•Yellow–Fatty–Nolonger produces blood

Two Types of Bone Development

Intramembraneous ossification; endochondral ossification

Where does intramembranous ossification take place?

Skull and clavicle

Key points to intramembranous ossification

–Startw/ soft CT, end up with bone–Osteoblastsreplace CT w/ spongy bone–Outersection of bone calcifies further to become compact bone–Resistscracking–Middleof bone remains spongy

Steps in intramembranous ossification

1) Condensationof CT into soft sheetpermeatedwith blood capillaries; -CTcells enlarge and turn into osteogenic cells

2) Depositionof osteoid tissue by osteoblastsonsurface; entrapment of firstosteocytes;formation of periosteum

3) Honeycombof bony trabeculae formed bycontinuedmineral deposition; creation ofspongybone

4)Surfacebone filled in by bone deposition,convertingspongy bone to compact bone.Persistenceof spongy bone in the middle layer

End result of intramembranous ossification? What happens with skull fractures?

Spongy bone sandwich; Skull fracture may leave innerlayer of compact bone unharmed

Key points to endochondral ossification

–Intracartilaginousossification—bone forming to replace a cartilage “model”–Mostbones in human body–Hyalincartilage into calcified cartilage–Calcifiedcartilage into spongy bone–Spongybone remodeled into either compact or spongy

Steps to endochondral ossification

1) Early cartilage model (perichondrium on outside; hyalin on inside)

2) Formationofprimaryossificationcenter,bonycollar, andperiosteum

3)Vascularinvasion,formationof primarymarrowcavity, andappearanceof secondaryossificationcenter

4)Boneat birth, withenlargedprimary marrowcavity and appearanceofsecondarymarrow cavityin one epiphysis

5)Boneof child, withepiphysealplate atdistalend

6)Adultbone with asinglemarrowcavityand closedepiphysealplate

How does cartilage change with endochondral ossification throughout childhood?

•During infancy and childhood, theepiphyses fill with spongy bone••Cartilage limited to the articular cartilage covering each joint surface, and tothe epiphyseal plate–Epiphysealplate persists through childhood and adolescence–Servesas a growth zone for bone elongation

Bone grows in which directions?

–Length– interstitial growth–Width –appositional growth

Where does bone elongation take place?

•Epiphyseal plate—region of transition fromcartilage to bone–growthzone–hyalinecartilage in middle–transitionzone on each side where cartilage is replaced by bone

Steps in bone elongation

1) Chondrocytes divide and produce collagen (cartilage) –add length to bone

2)Chondrocytesdie –leave space

3) Osteoblasts lay down bone matrix on top of cartilage base

Bone elongations –a result of cartilage growth withinthe epiphyseal plate

How does epiphyseal line form?

Epiphysealplate closes when cartilage is gone: •A line of slightly denser spongybone between epiphysis and diaphysis •Lengthwise growth is finished•Occurs at different ages (lateteens to early twenties)

Types of dwarfism

•Achondroplastic dwarfism–Long bones stop growing inchildhood•Normal torso, short limbs–Failure of cartilage growth inepiphyseal plate–Spontaneous mutation producesmutant dominant allele–

•Pituitarydwarfism–Lack of growth hormone–Normal proportions with shortstature

What is appositional growth?

•bonesincrease in width throughout life–Deposition of new bone at thesurface–Osteoblasts on deep side ofperiosteum deposit osteoid tissue–Osteoclasts of endosteum enlargemarrow cavity

What is bone remodeling?

•Throughoutlife—10% per year–Repairs microfractures,releases minerals into blood, reshapes bones in response to use and disuse–osteoblasts and osteoclasts workingtogether–Bone grows in response tomechanical stress•Racket arm of tennis players•Bones of athletes•Greater trochanter of children

Steps in healing of fractures

1) HematomaformationThehematoma is convertedtogranulation tissue by invasionofcells and blood capillaries.

2)Softcallus formationDepositionof collagen andfibrocartilageconverts granulationtissueto a soft callus.

3) Hardcallus formationOsteoblastsdeposit a temporarybonycollar around the fracture tounitethe broken pieces whileossificationoccurs.

4) BoneremodelingSmallbone fragments areremovedby osteoclasts, whileosteoblastsdeposit spongyboneand then convert it tocompactbone.

When does ossification occur?

•Ossification for a lifetime with growth andremodeling of bones