Bone Growth and Development[1]

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    Osteoprogenitor Cells

    The Stem Cells of bone

    Undifferentiated and have the potential to

    become either: Osteoblasts

    or

    Osteoclasts(Both of which respond to the hormones PTH

    and Calcitonin)

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    Osteoblasts

    Single-nucleated cells that FACILITATEMINERALIZATION

    Produce OSTEOID

    A liquid that crystallizes and eventually formsthe inorganic component of bone theMATRIX

    Once they are trapped within the matrix theycreate and can no longer move, they eitherDIE or BECOME OSTEOCYTES

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    Osteocytes

    Cells that remain in LACUNAE

    Lacunae are just spaces that contain osteocytes

    Connected to each other via extensions ofcytoplasm referred to as CANALICULI,

    which run perpendicular to HAVERSIAN

    SYSTEMS

    If they are on the outer edge of a bone, they

    flatten out and become bone lining cells

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    Osteoclasts

    Large, Multi-nucleated cells that function to EATAWAY AT BONE

    Thought to break down the inorganic component byproducing acids

    Thought to break down the organic component byproducing enzymes

    Very effective and can undo the work of 100osteoblasts

    Always associated with a blood supply Why?

    Because they are activated when there is too little calciumcirculating in the blood

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    Bone Resorption

    The work of OSTEOCLASTS

    It is a NORMAL PROCESS until itbecomes excessive, which is known as the

    pathological condition, osteoporosis

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    Bone

    Is a TISSUE

    It is a mixture of organic and inorganicmaterials that form a living tissue

    Provides support and protection for the body A framework for the other systems of the body

    Provides attachment sites for muscles

    Dr. Sauers definition: Bone is a complex network ofcells and a neurovascular system embedded in ahighly structural protein/mineral matrix

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    Bone

    Properties:

    Mineral component

    Organic componentGrowth centers

    Able to heal/regenerate

    Constantly changing

    Not expandable

    Hard/rigid (but microflexible)

    Impermeable (no diffusion through matrix)

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    Parts of a Typical Long Bone

    DIAPHYSIS

    a.k.a. the SHAFT or PRIMARY CENTER OFOSSIFICATION of the bone

    METAPHYSIS

    a.k.a. the area between the SHAFT and theEPIPHYSIS

    EPIPHYSIS a.k.a. the SECONDARY CENTER OF

    OSSIFICATION

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    PHYSIS

    A PHYSIS (osteologically speaking) is an area

    where there is bone growth actively taking

    place

    Growth stops when the PHYSIS is obliterated

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    Types of Bone

    SUBCHONDRAL

    CANCELLOUS COMPACT

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    Subchondral Bone

    Only located beneath articular cartilage

    Extremely vascular

    No periosteum

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    Cancellous Bone

    a.k.a. SPONGYbone

    TRABECULARBone (Lattice Structure) Type of bone in an infant/fetal skeleton

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    Bone Growth

    APPOSITION

    The laying down of new material

    REMODELING Breakdown and replacement of old material

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    Types of Bone Growth

    ENDOCHONDRAL

    Within Cartilage

    INTRAMEMBRANOUS

    Between Membranes

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    Cartilage

    Any word that includes the base, chondro,

    has something to do with cartilage

    Properties of CartilageRigid, but compressible

    Viscoelastic

    Avascular

    Expandable

    Cells are hydrophilic

    Does not regenerate

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    Endochondral Growth

    This is how most of the bones in the body grow

    and develop

    Stage 1:

    Starts with an ANLAGE An ANLAGE is just a cartilage model for bone

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    Endochondral Growth

    Stage 2

    Oldercartilage cells die and the matrix aroundthem ossifies

    This creates a place for bone to be laid down

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    Endochondral Growth

    Blood vessels carrying osteoblasts break in and

    begin to lay down PRIMARY SPONGIOSA

    (TRABECULAE)

    Cells start creating a PERIOSTEUM and an

    ENDOSTEUM

    These form a PERIOSTEAL COLLARaround the

    center of the bone

    *This is the PRIMARY CENTEROF OSSIFICATION

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    Endochondral Growth

    Eventually

    There is bone in the shaft and cartilage only at the

    ends

    The process repeats itself at the ends of the bones These locations are the SECONDARY CENTERS

    OF OSSIFICATION

    Also referred to as the EPIPHYSES

    Appear fordifferent bones at different times duringpeoples lives

    Development is complete when the cartilage between

    the epiphysis and diaphysis is no longer there and the

    parts unify to form a whole

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    Metaphysis Closure

    We have discussed what happens as bone

    growth occurs in the diaphysis and in the

    epiphyses, but what happens in that area

    between the two?

    Time for some more drawing

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    Intramembranous Growth

    Between Membranes

    Flat bones (like the parietals of the skull)

    Other bones of the skeleton once they develop

    the PERIOSTEUM and ENDOSTEUM

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    Intramembranous Growth:

    The Process The PERIOSTEUM has a FIBROUS LAYER

    and an OSTEOGENIC LAYER

    The osteogenic layer contains osteoblasts andlays down new bone

    Typically

    The PERIOSTEAL surface tends to beDEPOSITIONAL

    The ENDOSTEAL surface tends to be RESORPTIVE

    As bone grows, it incorporates blood vessels

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    Intramembranous Growth

    Occurs at the level of Cortical bone this is after

    lamellar bone has replaced the trabecular bone

    When new bone is produced by the osteogenic layer

    of the periosteum, blood vessels are incorporated

    These are referred to as PRIMARY OSTEONS and are

    NOT HAVERSIAN SYSTEMS

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    Intramembranous Growth

    HAVERSIAN SYSTEMS are known as

    SECONDARY OSTEONS

    They are formed within Lamellar bone They are responsible forremodeling the

    lamellar bone, which makes it stronger and

    replaces older bone with new bone

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    Haversian Systems

    Recall OSTEOCLASTS

    Osteoclasts eat away a resorptive spacewhich creates space for OSTEOBLASTS to

    lay down new bone

    This is all part of the BMU BasicMulticellular Unit

    Now Its time to do some picture pagestime to get

    your crayons and your pencils

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    Real-Life Application

    There are two reasons this is important toFORENSIC ANTHROPOLOGISTS

    SPECIES IDENTIFICATION

    Many animals have PLEXIFORMbone

    Looks like bricks

    No Haversian Systems (or if they have HaversianSystems, they are not configured like those of humans)

    AGEESTIMATION

    Useful for Forensic and Archaeological Cases

    By examining the number of haversian systems relativeto the amount of primary osteons and lamellar bone thatremains, the Forensic Anthropologist can determine theage of the individual