Download pdf - Bone Growth and Development[1]

8/8/2019 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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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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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