bio 2210 fall 11 skeletal tissues and bones

8/3/2019 BIO 2210 FALL 11 Skeletal Tissues and Bones

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BIO 2210

Skeletal Tissuesand Bones

Chapter 6


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Cells and Tissues

RECALL : The Four Primary Tissue Types that

compose the body are:- Epithelial Tissues : tissues that cover or line astructure, and that form Glands .

-Connective Tissues : tissues that providea supporting function.

- Muscle Tissues : tissues that provide movement.- Nervous Tissues : tissues that serve a control role.

[ Recall : Cartilage and Bone are Connective Tissues that are derived

from the embryonic Mesoderm during Organogenesis .]


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Cartilage: A Connective Tissue

There are three varieties of Cartilage :1. Hyaline Cartilage

2. Elastic Cartilage

3. Fibrocartilage

All three types of Cartilage are associated with the Human Skeleton.


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Hyaline Cartilage


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Elastic Cartilage


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Fibrocartilage


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Cartilages and the Human Skeleton


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Hyaline Cartilages and the Skeleton

Skeletal HyalineCartilages include:

Articular* Cartilages ,which cover the ends of most Bones at moveable

Joints .

Costal Cartilages ,which connect the Ribsto the Sternum(breastbone).

* Articulation : a Joint

between inflexible parts.


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Hyaline Cartilages

Respiratory Cartilages , which form the skeleton of

the Larynx and reinforce the Respiratory Passageways . Nasal Cartilages , which support the External Nose .


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Elastic Cartilages and the Skeleton Elastic Cartilagesoccur in twolocations:

the External Ear .

the Epiglottis , alaryngeal, flap-like structure thatcloses when we

swallow soingestedsubstances do notenter the Larynxand airways.


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Fibrocartilages and the Human Skeleton

Fibrocartilages occur atsites that are subjected toheavy pressure and

stretch, such as the pad-like cartilages ( Menisci )of the Knee , the discs

between the Vertebrae( Intervertebral Discs ),and the Pubic Symphysis .


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Cartilages Cartilages are not innervated and generally contain no Blood Vessels .

Cartilages are often surrounded by a layer of Dense IrregularConnective Tissue called the Perichondrium , which contains Blood Vessels .

The Perichondrium acts like a girdle by resisting outwardexpansion when Cartilage is compressed.

The structure labeled asP in the

photomicrograph is the Perichondrium


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Cartilages

Cartilages grow in two ways:

1. Appositional Growth (outward expansion due to theproduction of new Cartilage Matrix on the outer surface of acartilagenous structure). Cartilage-forming cells(Chondroblasts ) in the surrounding Perichondrium secrete

new Matrix on the surface of existing cartilage tissue. 2. Interstitial Growth : Chondroblasts in Lacunae divide and

secrete new Matrix , thereby expanding a cartilagenousstructure from within.

Cartilage growth ends when the Skeleton stops growing.

During old age, Calcium Salts may be deposited in the Matrix of Cartilage (Calcification ), which causes theCartilage to harden and become more rigid and brittle.


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Bone (Osseous) Tissue


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Functions of Bones

Support: bones support the body and cradles the bodys soft organs.

Protection: bones encase many body structures, e.g., the Skull protectsthe Brain , the Vertebrae surround the Spinal Cord , the Rib Cageprotects organs in the Thoracic Cavity , and the Pelvic Girdle cradlesorgans in the Pelvic Cavity .

Movement: Skeletal Muscles attach to Bones by Tendons and use Bones as Levers to provide Movement .


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Functions of Bones

Mineral Storage: Bone serves as a reservoir for

Minerals , especially Calcium and Phosphate .

Blood Cell Formation: Blood Cells are formed in Bone Marrow by a process called Hematopoiesis .

Potential Energy Source: Fat is stored in BoneCavities .


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Bones

Bones are Organs . [Recall: Organs arecomposed of different Tissues .]

Bones contain Osseous Tissue (the mostdominant tissue type), Nervous Tissue formstheir Nerves , Cartilage is present in their

Articular Cartilages , Fibrous ConnectiveTissue lines their surfaces and cavities, and

Epithelial Cells and Smooth Muscle Cellsare present in their Blood Vessels .


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Bone (Osseous Tissue): Composition Osseous Tissue consists of both Organic and

Inorganic Substances .

Organic Components include Cells called Osteoblasts ,Osteocytes , and Osteoclasts , and Osteoid , which is the organicpart of the Bones Matrix .

The Osteoid makes up ~1/3 of the Bones Matrix , and iscomposed of Ground Substance ( Proteoglycans andGlycoproteins ) and Collagen Fibers , which are produced byOsteoblasts .

The remaining 65% of Bone consists of Inorganic Mineral Salts called Hydroxyapatites , which form tiny crystals thatsurround the Collagen Fibers .

The crystals [Ca10

(PO 4 )

6 (OH)

2 ] give its hardness and strength.


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The Bones: Learn them!!!

The Human Body contains 206 Bones , which aredivided into two generalgroups:

Axial Skeleton: bones that

form the long axis of thebody, including the Skull ,Vertebral Column , and RibCage (Bony Thorax) .

Appendicular Skeleton:bones of the upper and lowerlimbs , and the girdles(shoulder bones and hip

bones) that attach the limbsto the Axial Skeleton .


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Bone Markings; learn them!!!

Note: Bone Markings are anatomical landmarks that reveal sites of muscle

attachments, points of articulation, and sites of blood vessels and nerveassa ewa s.


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Bone Markings: Learn them!!!


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Classification of Bones

Bones are classified by their shapes:

Long Bones: considerably longer than they are wide, e.g., longlimb bones, finger bones.

Short Bones: roughly cube shaped, e.g., bones of the wrist(Carpals ) and ankle ( Tarsals ). [Note: Sesamoid Bones: shortbones that form in a tendon, most notably the Patella (kneecap).

Flat Bones: thin, flattened and usually somewhat curved bones,

e.g., the Sternum (breastbone), the Ribs , the Scapulae(shoulder blades), and most Skull Bones .

Irregular Bones: bones with complicated shapes, including the

Vertebrae and hip bones ( Coxae ).


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Classification of Bones According to Their Shapes


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General Bone Anatomy

Every Bone has an external

dense layer composed of Compact Bone that appearssmooth and solid.

Internal to Compact Bone isSpongy Bone (Cancellous

Bone ), which hashoneycomb-like spaces, or,in the case of Long Bones , a

Medullary Cavity .The needle -like or flatbone pieces that formSpongy Bone are called

Trabeculae .Note : In Flat Bones , Spongy Bone iscalled Diploe .


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Typical Long Bone Structure Diaphysis: thetubular shaft thatforms the boneslong axis.

The Diaphysis isconstructed of a

relatively thick collar of Compact Bone thatsurrounds a

Medullary Cavityor Marrow Cavity .

In adults, the Medullary Cavitycontains Fat(Yellow Marrow ).


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Long Bone Structure

Epiphyses (Epiphysis ,

singular): the moreexpanded bone ends.

Compact Bone forms theexterior of the Epiphysesand the interiors of theEpiphyses containSpongy Bone .

The surfaces of Epiphyses at Joints arecovered with a thin layerof Articular (Hyaline)

Cartilage .


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Long Bone Structure

An Epiphyseal Line islocated between the

Diaphysis and each Epiphysis .

The Epiphyseal Lineis a remnant of the

Epiphyseal Plate , adisc of HyalineCartilage that growsduring childhood tolengthen the Bone .

The Epiphyseal Lineor Epiphyseal Plate inchildhood issometimes called the Metaphysis .


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Periosteum

With exception of Joint surfaces,

Long Bones (and other Bones ) arecovered by a double -layeredmembrane called the Periosteum .

The Outer Fibrous Layer consists of Dense Irregular Connective Tissue .

The inner or Osteogenic Layerabutting the bone surface consists of

bone-forming cells calledOsteoblasts , bone-destroying cellscalled Osteoclasts , and Stem Cellscalled Osteogenic Cells that give

rise to Osteoblasts .

B A i d C ll T


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Bone-Associated Cell Types


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Periosteum

The Periosteum is attached tounderlying bone by Perforating(Sharpeys) Fibers , which areCollagen Fibers that extend fromthe fibrous layer into the Bone

Matrix .

The Periosteum is supplied with Nerve Fibers and Blood and Lymphatic Vessels , which enter

the Diaphysis via a Nutrient Foramen .

The Periosteum providesanchoring points for Tendons and

Ligaments .


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Long Bone Structure

Internal bone surfaces,

including Spongy BoneCavities , are covered by adelicate connective tissuemembrane called the

Endosteum .

The Endosteum also linescanals that pass through

Compact Bone .Like the Periosteum , the

Endosteum contains

Osteoblasts and Osteoclasts .

Mi f O O bl d O l


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Microscopy of Osteocytes, Osteoblasts, and Osteoclasts

Osteocyte s are encased in Lacunae of a bones Matrix .

Osteoblasts are found in rows on the internal and externalsurfaces of Bone .

Osteoclasts are large, multinucleated cells found on the internal

and external surfaces of Bone .

f h l d l


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Structure of Short, Irregular, and Flat Bones

Short, Irregular, and Flat Bonesall consist of relatively thin platesof Periosteum - covered Compact

Bone on their surfaces and Endosteum-lined Spongy Boneon the inside.

Red Bone Marrow is present inthe Spongy Bone .

Short , Irregular , and Flat Bones have no Diaphysis or Epiphyses .

H i i (Bl d F i ) Ti i B


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Hematopoietic (Blood Forming) Tissue in Bones

Hematopoietic Tissue called Red Bone Marrow , is found in theTrabecular Cavities of the

Epiphyseal Spongy Bone of Long Bones .

Hematopoietic Tissue is alsolocated in the Spongy Bone of Short, Flat, and Irregular Bones(such as the Hip Bones ).

Yellow Marrow in MedullaryCavities can be replaced by Red

Marrow in very Anemic

individuals.

Mi A t f C t B


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Micro-Anatomy of Compact Bone

Though appearing dense and solid

macroscopically, microscopy revealsthat Compact Bone is riddled withpassageways that contain Nerves ,and Blood and Lymphatic Vessels .

Mi A f C B


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Micro-Anatomy of Compact Bone The structural unit of Compact Bone is

called the Osteon orthe Haversian System .

An Osteon is a group

of tubes of Bone Matrix , one placedoutside the next likegrowth rings in a tree

trunk.Each Osteon functionsas a tiny weight

bearing pillar.

Compact Bone and Osteons


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Compact Bone and Osteons

Micro Anatomy of Compact Bone


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Micro-Anatomy of Compact Bone Each matrix tube is a Lamella (little plate).

Collagen Fibers in a particular Lamella run in a singledirection, while Collagen Fibersin adjacent Lamellae arearranged in opposite directions.

The tiny crystals of Hydroxyapatite align with theCollagen Fibers so theyalternate in direction in adjacent

Lamellae .The Collagen Fibers give

Bones their tensile strength(ability to resist stretching) andthe Hydroxyapatites make

Bones hard.

Mi A t f C t B


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Micro-Anatomy of Compact Bone

A Central or HaversianCanal runs through thecore of each Osteon .

Haversian Canals containsmall Blood Vessels and

Nerves that serve theneeds of the OsteonsCells .

Other canals, called Perforating orVolkmanns Canals lie at

right angles to the longaxis of the bone andconnect the blood andnerve supply of the

Periosteum to those of the Haversian Canals and the Medullary Cavity .

Micro Anatomy of Compact Bone


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Micro-Anatomy of Compact Bone Lacunae occur at the junctions of the Lamellae .

Small canals calledCanaliculi connect the Lacunae to one anotherand to the HaversianCanal .

During Bone Formation ,Osteoblasts produce Bone

Matrix and maintaincontact with one anotherby tentacle-likeprojections that containGap Junctions .

Spider-shaped Osteocytes(mature bone cells)occupy the Lacunae .

The Osteocytes in the Lacunae are structurally and functionally linked via their cytoplasmic extensions into

the Canaliculi and by way of the Gap

Junctions they form with one another.

Compact Bone


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Compact BoneNot all Lamellae are part of Osteons .

Incomplete Lamellae called Interstitial Lamellae occurbetween Osteons . They areformed between Oseons orare remnants of formerOsteons that remain after

Bone Remodeling .

Circumferential Lamellaeare located beneath the

Periosteum . They extendaround the entirecircumference of the

Diaphysis and effectivelyresist twisting of a Long

Bone .

Micro Anatomy of Spongy Bone


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Micro-Anatomy of Spongy Bone

Only a few cells thick, the Trabeculaeof Spongy Bone contain irregularlyarranged Lamellae and Osteocytes thatare interconnected by Canaliculi .

Unlike with Compact Bone , noOsteons per se are present in Spongy

Bone .

Nutrients reach the Osteocytes inSpongy Bone by diffusing through theCanaliculi from Capillaries in the

Endosteum surrounding theTrabeculae .

Spongy Bone contains Red Bone Marrow , which produces Bloods Red Blood Cells , White Blood Cells , and Platelets .

Red Bone MarrowSpongy Bone

Ossification/Osteogenesis (Bone Formation)


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Ossification/Osteogenesis (Bone Formation) Bones form from two general Processes:

1. Intramembranous Ossification: formation of the Flat Bones(Cranial Bones ) of the Skull ( Frontal , Parietal , Occipital andTemporal Bones ) and the formation of the Clavicles from FibrousConnective Tissue .

Intramembranous Ossification begins at about Week 8 of Gestation .

Bones formed by Intramembranous Ossification are called Membrane Bones .

2. Endochondral Ossification: formation of all other Bones beginsduring the Second Month of Gestation and involves the replacementof Hyaline Cartilage structures with Bone Tissue .

Bones formed by Endochondral Ossification are called Endochondral Bones .

[Note:Before

Week 8of

Gestation, the

Skeletonof a

Human Embryoisconstructed entirely from Fibrous Membranes and Hyaline Cartilage .]

Steps Involved in Intramembrane Ossification


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Summary of Intramembranous Ossification


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y

Intramembranous Ossification


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Initial Steps Involved in Endochondral Ossification


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Initial Steps Involved in Endochondral Ossification Endochondral Ossificationuses Hyaline Cartilagebones as patterns for bone

construction.The process begins at thecenter of a Hyaline CartilageShaft as the Perichondrium(not shown in figure)

becomes infiltrated with Blood Vessels .

The Perichondrium convertsinto a vascularized

Periosteum (also not shownin figure).

Osteoblasts of the newlyformed Periosteum secreteOsteoid against the HyalineCartilage Diaphysis , encasingit in a Bone Collar .

[RECALL: Osteoid is the organic partof the Bone Matrix consisting of Ground Substance ( Proteoglycans and Glycoproteins ) and Collagen Fibers ).]

Subsequent Steps Involved in Endochondral Ossification


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q p

Chondrocytes within theshaft undergoHypertrophy (enlarge insize) and signal thesurrounding CartilageMatrix to Calcify .

The Diffusion of nutrientsbecomes limited by theformation of the Calcified

Matrix , so theChondrocytes die and theCartilage Matrixdeteriorates, causing the

formation of cavities.

Steps Involved in Endochondral Ossification


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During Month 3 , the

forming cavities areinvaded by a collectionof elements called the Periosteal Bud .

The Periosteal Bud contains a Nutrient

Artery and Vein , Nerve

Fibers , Red MarrowComponents ,Osteoblasts , andOsteoclasts .



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Entering Osteoclasts

further erode the Calcified Cartilage Matrix .

Osteoblasts secrete Osteoid around the remaining

fragments of HyalineCartilage , forming bone-covered CartilageTrabeculae .

The Bone-Covered Cartilage Trabeculae arethe earliest version of Spongy Bone in

developing Long Bones .



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As the Primary OssificationCenter enlarges, Osteoclastsbreak down the newly formedSpongy Bone and open a

Medullary Cavity in the center of the Diaphysis .

At Birth , most of our Long Bones have a Bony Diaphysissurrounding remnants of Spongy

Bone , a widening MedullaryCavity , and two mainlyCartilagenous Epiphyses .

Around the time of Birth ,Secondary Ossification Centersdevelop in the Epiphyses , and the

Epiphyses gain bony tissue after

Birth.

Summary of Endochondral Ossification


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Fetal Skeleton


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Fetal Skeleton

By Birth , most Long Bones of the Skeletonare Ossified , except fortheir Epiphyses .



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When SecondaryOssification is complete,(i.e., the conversion of

Hyaline Cartilage to BoneTissue in the Epiphyses ),

Hyaline Cartilage remains in

two places:1) on the Epiphyseal Surfaces as ArticularCartilages , and

2) at the junctions of the Diaphysis and Epiphyses ,where it forms Epiphyseal

Plates .

Postnatal Bone Growth


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Postnatal Bone Growth

During infancy and youth, Long Bones lengthen byInterstitial Growth of the Epiphyseal Plates andall Bones grow in thickness by Appositional

Growth.

Most Bones stop growing during Adolescence .

However, some Facial Bones , such as those of the Nose and the Mandible (lower jaw), continue togrow almost imperceptively throughout life.

Growth of Long Bone Length


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Interstitial Growth:

On the side of the Epiphyseal Platefacing an Epiphysis , Cartilage in aregion called the Resting orQuiescent Zone is relativelyinactive.

The Epiphyseal Plate Cartilagefacing the Diaphysis , on the otherhand, organizes into a pattern thatallows for fast growth.

In this Growth Zone , the Cartilage

Cells undergo Mitosis and form tallcolumns like coins in a stack.

The rapidly dividing cells push the Epiphysis away from the Diaphysis , causing the Bone tolengthen.



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g g

Older Chondrocytes that are closerto the Diaphysis undergo

Hypertrophy and their Lacunae

erode and enlarge ( the Hypertrophic Zone ).

Subsequently, the surroundingCartilage Matrix calcifies, theCartilage Cells die and deteriorate

in a region called the Calcification Zone .

Long calcified Cartilage Spiculesremain at the Epiphysis-Diaphysis

junction.

In the Ossification Zone , theCartilage Spicules are partlyeroded by Osteoclasts and quicklycovered with Bone Matrixproduced by Osteoblasts , formingSpongy Bone .



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During growth, the Epiphyseal Plate maintains a constantthickness because the rate of Cartilage Growth on its Epiphysis -facing side is balanced by thereplacement with Bony Tissue onits Diaphysis -facing side.

As adolescence draws to an end,the Chondroblasts of the

Epiphyseal Plate divide less oftenand the plates become thinner andthinner until they are entirelyreplaced by Bone Tissue .

Longitudinal Bone Growth ceaseswhen the Bony Tissues of the

Epiphyses fuse with the Bone of the Diaphysis .

Long Bone Growth


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g Longitudinal Bone Growth ceases when the BoneTissue of the Epiphyses and Diaphysis fuses, called

Epiphyseal Plate Closure , which usually occurs at ~18and ~21 years of age in females and males,respectively.

Longitudinal Bone Growth is accompanied by almostcontinuous Remodeling of the Epiphyseal Ends tomaintain the proper proportions between the Diaphysis

and Epiphyses .[Note: Adult Bone can continue to increase in diameteror thickness by Appositional Growth if stressed by

excessive muscle activity or body weight. ]

Appositional Bone Growth


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pp

Ossification


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Further Notes on Bone Growth :

In Short Bones , only Primary

Ossification Centers form.

In most Irregular Bones , bone

formation occurs from several distinctOssification Centers .



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g g

During BoneGrowth, a bone

undergoes Bone Remodeling tomaintain its proper

bone proportions.

Regulation of Bone Growth


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g

During infancy and childhood, the most important

stimulus of Epiphyseal Plate activity is Growth Hormone , which is secreted by the anterior lobe( Adenohypophysis ) of the Pituitary Gland .

Hypersecretion of Growth Hormone in children resultsin excessive height ( Gigantism )

Thyroid Hormones produced by the Thyroid Gland

modulate the activity of Growth Hormone and helpsensure bones grow in proper proportions.

Deficits in Growth Hormone and Thyroid Hormone

produce characteristics of Dwarfism .

Regulation of Bone Growth by Sex Hormones


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g y

At Puberty , Sex Hormones (Testosterone in themale, Estrogen in the female) are produced inincreasing amounts, initially producing thegrowth spurt typical of adolescence.

Sex Hormones additionally cause theMasculinization of some bones in males and the

Feminization of some bones in the female.Thereafter, the Sex Hormones induce Epiphyseal Closure , ending Longitudinal Bone Growth .

Bone Resorption/Remodeling


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p g

Small scale changes in bone architecture occurs

continuously in our bodies as Bone is Resorbed and New Bone is formed.

Every week, we recycle 5-7% of our Bone Mass and up to0.5 g of Calcium may enter and/or leave the adult skeletondaily.

Compact Bone is replaced ~every 10 years .

Spongy Bone is replaced ~every 3-4 years .

[Note: Bone Replacement is necessary because when boneremains in place for long periods, extensive CalciumCrystallizations over time make bone more brittle and subject to

breakage. ]

Osteoclasts and Bone Resorption/Remodeling


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p g

Osteoclasts are large,multinucleated cells that arisefrom the same HematopoieticStem Cells that produce

Macrophages .

Osteoclasts produce Lysosomal Enzymes thatdigest the organic Bone

Matrix , and they additionallyproduce Hydrochloric Acid ,

which dissolves CalciumSalts .

As a result, pits called Howships Lacuna formwhere Bone is removed.

Remodeling and Interstitial Lamellae


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Howships Lacunaformed by Osteoclasts

enlarge to form Absorption Cavities ,which become invadedby Blood Vessels , andOsteoblasts enter thecavities where theydeposit new Concentric

Lamellae around theblood vessels, thusforming new HaversianSystems .

Interstitial Lamellaeobserved in Bone areusually remnants of remodeled HaversianSystems .

Bones and Mechanical Stress


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Wolffs Law : a bone grows or remodels in response

to the demands placed on it. Long Bones are thickest midway along the Diaphysis wherebending stresses are greatest.

Curved Bones are thickest where they are most likely tobuckle.

The Trabeculae of Spongy Bone forms struts along lines of compression.

Large, Bony Projections occur where heavy, active musclesare attached.

[Note : Wolffs Law explains the featureless bones of the fetus

and the Atrophied of bones of bedridden people. ]



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Wolffs Law : a bone grows or remodels in response to the demands placed on it.

Regulation of Remodeling


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Bone Remodeling is regulated bytwo control loops:

Negative Feedback Hormonal Mechanisms that maintain Ca ++

levels in the Blood .

Responses to Gravity and Mechanical Forces .



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Details about the mechanism(s) by which

Bones respond to Mechanical Stressremain unclear, but

Bone Deformation produces an Electrical Current , asdo some minerals when stressed ( Piezo Electric

Effect ).

Stretched and compressed bone regions are oppositely

charged. Bone Tissue is deposited in negatively chargedregions of stress, and bone is absorbed in unstressed

areas of positive charge.

Hormonal Regulation of Blood Calcium


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The body contains ~1,200-1,400 g of Calcium (Ca ++ ),

with >99% as Bone Minerals .

Most of the remainder is in Extracellular Fluids and in

Cells .

In addition to Bone Formation , Ca ++ isnecessary for: 1) Nerve

Impulse Transmission , 2) Muscle Contraction , 3) Blood Coagulation , 4)Secretion by Glands , and 5)

Cell Division .



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Calcium Absorptionfrom the Small

Intestine is under thecontrol of Vitamin Dmetabolites producedby the Skin .



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Hypercalcemia (sustainedhigh blood levels of Ca ++)can result in thedeposition of calciumsalts in blood vessels,kidneys and other softorgans, which hamperstheir functions.

Note: the role of physiologic

concentrations of Calcitonin in regulatingthe deposition of CalciumSalts is now beingseriously questions.

Bone Fractures


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Bone Fracture = Bone Break

Bone Fractures during youth usually occursas a result of exceptional trauma, e.g., sports

injuries, auto accidents, falls.

Bone Fractures in old age frequently occur

because bones have become thin andweakened.

Bone Fractures


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Fracture Classifications

Nondisplaced Fractures: bone ends retain their normal positions.

Displaced Fractures: bone ends are out of normal alignment.

Complete Fracture: bone is broken through.

Incomplete Fracture: bone is not completely broken through.

Linear Fracture: bone break parallels the bones long axis.

Transverse Fracture: bone break is perpendicular to the bones longaxis.

Open (Compound) Fracture: broken bone penetrates the skin.

Closed (Simple) Fracture: broken bone does not penetrate the skin.

Bone Fractures


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Bone Fractures


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Bone Fractures


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Bone Repair


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A Fracture is treated by Reduction, which is therealignment of the broken bones.

Closed Reduction: the bone ends are coaxed into

place by the physician.Open Reduction: the bone ends are secured surgicallywith pins or wires or screws and plates.

After a broken bone is Reduced , it is immobilizedeither by a cast or traction.

Stages of Bone Repair


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1. When a bone breaks, Blood Vessels in the Bone and Periosteum aretorn and Hemorrhage , causing a mass of clotted blood ( Hematoma )to form at the fracture site.

Bone Cells derived of nutrition die, the tissue at the injured site

becomes swollen, painful, and inflamed.



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2. Within a few days, Capillaries grow into the Hematoma ,

Phagocytic Cells endocytose debris, invading Fibroblastsproduce Collagen Fibers that span the break, some Fibroblastsdifferentiate into Chondroblasts that secrete Collagen Matrix ,and Osteoblasts begin forming Spongy Bone .

The entire mass of repair tissue, called the FibrocartilaginousCallus , splints the broken Bone .



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3. Within a week, new Trabeculae appear and the Fibrocartilaginous Callus converts to a Bony (hard) Callus of Spongy Bone .

Bony Callus formation continues until a firm union between the

broken Bone parts is formed over a two month period.



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4. During Bony Callus formation and continuing for severalmonths thereafter, the Bony Callus undergoes Remodeling .

The Medullary Cavity is reformed and Compact Bone is

laid down to reconstruct the walls of the Bone .

Osteoporosis


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Osteomalacia: a condition in which bones are notadequately Mineralized .

Osteoporosis : disease in which Bone Resorptionoutpaces Bone Deposition .

Bone Mass is reduced, causing bones to break easily.

Spongy Bone is most vulnerable, and Compression Fractures of the Vertebrae are common.

The neck of the Femur is also very susceptible and prone tofracture (broken hip).

[Note : Osteoporosis occurs most often in the aged, particularlyin postmenopausal women.]

Osteoporosis


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Osteoporosis isfrequently treated with

Calcium , Vitamin D supplements , weight- bearing exercise , and Hormonal (Estrogen) Replacement Therapy(HRT) .

Osteomalacia: Rickets


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Rickets: analogous to Osteoporosis , but in children.

Hallmarked by bowed legs and deformities of thepelvis, skull, and rib cage.

Epiphyseal Plates cannot be calcified, so theycontinue to widen and the ends of long bones becomevisibly enlarged and abnormally long.

Rickets is caused by insufficient Calcium in the diet

or by Vitamin D deficiency .Treatment: Vitamin D-Fortified Milk and exposure tosunlight to stimulate Vitamin D production by the

Skin . Other Clinical Conditions and Terms


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Achondroplasia: a congenital condition involving

defective Cartilage and Endochondral BoneGrowth so that limbs are too short; a type of Dwarfism .

Ostealgia: pain in a Bone .

Osteitis: inflammation of Bony Tissue .

Osteomyelitis: inflammation of Bone and Bone Marrow caused by pus-forming bacteria thatenter the body via a wound.

Other Clinical Conditions and Terms P t Di h t i d b i d h h d B


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Pagets Disease: characterized by excessive and haphazard Bone Deposition and Resorption at a usually localized site, with the Pagetic Bone having an abnormally high ratio of Spongy Bone to Compact

Bone and reduced Mineralization . Pagets Disease occurs in ~3% of elder North American people, it generally affects the Spine , Pelvis , Femur and Skull , and its Etiology (cause) is unknown [ Note: someevidence suggests it may be caused by a Virus ].

Bony Spur: abnormal projection from a bone due to bony overgrowth;common in aging bones.

Osteosarcoma: a form of Bone Cancer typically arising in a Long Bone of a limb and most often in patients that are 10-25 years old.Osteosarcomas grow aggressively, they painfully erode bone, and theytend to Metastasize to the Lungs .

Leukemias: a group of cancerous conditions involving the Bone Marrowand White Blood Cells . In all Leukemias , the Bone Marrow becomes

bio 2210 fall 11 skeletal tissues and bones

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