1

Skeletal SystemSkeletal System

The skeletal System . . .What are the general components of the skeletal system?What does the skeletal system do for you & how does it achieve these functions?

Components

The skeletal system includes:BonesCartilages

Mainly hyaline & fibrocartilageJointsLigamentsOther connective tissues

Such as adipose, areolar…

2

General Functions

Functions of the Skeletal SystemSupport against gravityProtection of soft internal organsLeverage for muscle action

Insertions & originsStorage

Calcium, phosphorous, other inorganic saltsFat - energy

Blood cell production

Bone Structure - Macroscopic

Bone Shapes:LongShortFlatIrregular

Other: Wormian (sutural) & Sesamoid bones

Bone Structure: The generic boneThe shaft of a bone = diaphysisThe ends of a bone = epiphyses

Covered with articular cartilageThe cavity of a bone = marrow cavity

Loose connective tissueOuter covering = periosteum

Point of attachment for?Also location of many blood vessels & nerves

Inner lining = endosteumLines marrow cavityActive during growth & remodeling

Bone tissue presentSpongy (cancellous) in epiphyses & marrow cavityCompact in shaft and lining periphery of bone

3

Composition of Bones: MicroscopicTissues Present in bone

Dense connective tissue – the periosteumAn outer fibrous layerAn inner cellular (osteogenic layer)

Loose connective tissue – bone marrowosseous – compact & spongycartilage – hyalineBloodnervous

Composition of Bone: Microscopic

Osseous or bone tissue has:Specialized cells

2% of bone weightStrong flexible matrix

Calcium phosphate crystalsTwo-thirds of bone weight

Collagen fibers

Cells of Osseous TissueOsteoblasts

Responsible for bone deposition (laying down new bone) = osteogenesis

OsteocytesResponsible for maintenance of bone tissue in the lacunae of the osteon

Recycle the mineral componentsOsteoclasts

These cells are derived from white blood cellsmulti-nucleate cellsInvolved with bone resorption (osteolysis) by secreting enzymes that dissolve bony matrix

4

Organization of Bone Tissue

Bone that is highly organized is called compact bone

Organized units are called osteonsBone that is not in a highly compacted structure is spongy bone

plates are called trabeculaeTrabeculae in large help to increase the strength of bone

The OsteonBasic functional unit of

compact bone; columnar & cylindrical in shape

Strong in long axis of boneConcentric layers of osteocytesConcentric layers of matrix (lamellae)Central (Haversian) canal

Axial tunnel for blood vessels

Perforating canal (Volkmann’s)

Radial tunnel for blood vessels

Osteocytes communicate via small canals through the lamallae called canliculi

Bone Formation & Growth

Two methods of forming bones1. Intramembranous Ossification

Ossification—Process of converting other tissues to boneForms flat bonesStem cells differentiate to osteoblastsProduces spongy bone, then compact bone

2. Endochondral Ossification

Bone Formation in 16 Week Old Fetus

5

Bone Formation and Growth

Endochondral OssificationMost bones formed this wayCartilage model replaced by boneReplacement begins in middle (diaphysis)Replacement follows in ends (epiphyses)

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Cartilagemodel

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis

6

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis Marrowcavity

Primaryossificationcenter

Bloodvessel

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.

The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis Marrowcavity

Primaryossificationcenter

Bloodvessel

Marrowcavity

Bloodvessel

Endochondral OssificationPLAY

Enlargingchondrocytes within

calcifying matrix

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calicifies.

Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.

The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone.

Blood vessels invade the epiphyses and osteo-blasts form secondary centers of ossification.

Cartilagemodel

Boneformation

Epiphysis

Diaphysis Marrowcavity

Primaryossificationcenter

Bloodvessel

Marrowcavity

Bloodvessel

Secondaryossificationcenter

Epiphysealcartilage

Articularcartilage

7

Bone GrowthAppositional vs. Transitional Bone Growth

Bone Formation and Growth

Requirements for Normal Bone GrowthMinerals

Calcium, phosphateVitamins

Vitamin D3Vitamin CVitamin A

HormonesGrowth HormoneSex hormones, thyroid hormone, others

Bone Remodeling/Homeostasis

Role of Remodeling in SupportRemodeling—Continuous breakdown and reforming of bone tissueShapes reflect applied loadsMineral turnover enables adapting to new stresses

8

Bone Remodeling/HomeostasisHomeostasis and Mineral Storage

Bones store calciumContain 99% of body calciumStore up to two kg calciumHormones control storage/release

PTH, calcitriol release bone calciumCalcitonin stores bone calcium

Blood levels kept constant

Bone Remodeling/HomeostasisInjury and Repair

Fracture—A crack or break in a boneSteps in fracture repair

Fracture hematomaMitoses in periosteum, endosteum

Internal callusExternal callus

Bone remodeling

Bonefragments

Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot, or fracture hematoma, develops.

Fracturehematoma

Deadbone

9

Bonefragments

Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot, or fracture hematoma, develops.

Fracturehematoma

Deadbone

NewbonePeriosteum

Spongy boneof internal

callus

Cartilageof external

callus

An internal callus forms as a network of spongy bone unites the inner edges, and an external callus of cartilage and bone stabilizes the outer edges.

Figure 6-74 of 5

Bonefragments

Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot, or fracture hematoma, develops.

Fracturehematoma

Deadbone

NewbonePeriosteum

Spongy boneof internal

callus

Cartilageof external

callus

An internal callus forms as a network of spongy bone unites the inner edges, and an external callus of cartilage and bone stabilizes the outer edges.

The cartilage of the external callus has been replaced by bone, and struts of spongy bone now unite the broken ends. Fragments of dead bone and the areas of bone closest to the break have been removed and replaced.

Internalcallus

Externalcallus

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Steps in the Repair of a FracturePLAY

Bonefragments

Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot, or fracture hematoma, develops.

Fracturehematoma

Deadbone

NewbonePeriosteum

Spongy boneof internal

callus

Cartilageof external

callus

An internal callus forms as a network of spongy bone unites the inner edges, and an external callus of cartilage and bone stabilizes the outer edges.

The cartilage of the external callus has been replaced by bone, and struts of spongy bone now unite the broken ends. Fragments of dead bone and the areas of bone closest to the break have been removed and replaced.

A swelling initially marks the location of the fracture. Over time, this region will be remodeled, and little evidence of the fracture will remain.

Internalcallus

Externalcallus

Externalcallus

10

Aging and the Skeletal SystemOsteopenia—Less than normal ossification (mineral content) in bone

Osteopenia starts before age 40Women lose 8% per decadeMen lose 3% per decade

Spongy bone most affected

EpiphysesVertebraeJaws

The Skeleton - Terms

11

The Skeleton Divisions

AxialCreates the support basis for the arms and legsProvides protection for the brain & spinal cord, as well as the heart & lungs

AppendicularThe arms & legsProvide movement of the body

Higgins - control yourself & sit down!