Bones The Support System and More. Skeletal Cartilage Contains no blood vessels or nerves Contains no blood vessels or nerves Surrounded by the perichondrium.

BonesBones

The Support System and MoreThe Support System and More

Skeletal CartilageSkeletal Cartilage

Contains no blood vessels or nervesContains no blood vessels or nerves Surrounded by the perichondrium Surrounded by the perichondrium

(dense irregular connective tissue) (dense irregular connective tissue) that resists outward expansionthat resists outward expansion

Three types Three types HyalineHyaline ElasticElastic fibrocartilagefibrocartilage

Hyaline CartilageHyaline Cartilage

the most abundant skeletal cartilagethe most abundant skeletal cartilage Support, flexibility, and resilienceSupport, flexibility, and resilience

Present in these cartilages:Present in these cartilages: Articular – covers the ends of long bonesArticular – covers the ends of long bones Costal – connects the ribs to the sternumCostal – connects the ribs to the sternum Respiratory – makes up the larynx and Respiratory – makes up the larynx and

reinforces air passagesreinforces air passages Nasal – supports the noseNasal – supports the nose

Elastic CartilageElastic Cartilage

Similar to hyaline cartilage but Similar to hyaline cartilage but contains elastic fiberscontains elastic fibers

Found in:Found in: the external earthe external ear the epiglottisthe epiglottis

FibrocartilageFibrocartilage

Highly compressed with great tensile Highly compressed with great tensile strengthstrength

Contains collagen fibersContains collagen fibers Found in:Found in:

menisci of the kneemenisci of the knee intervertebral discsintervertebral discs

Growth of CartilageGrowth of Cartilage

Appositional Appositional cells in the perichondrium secrete matrix cells in the perichondrium secrete matrix

against the external face of existing cartilageagainst the external face of existing cartilage Interstitial Interstitial

lacunae-bound chondrocytes inside the lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, cartilage divide and secrete new matrix, expanding the cartilage from withinexpanding the cartilage from within

Calcification of cartilage occursCalcification of cartilage occurs During normal bone growthDuring normal bone growth During old ageDuring old age

Classification of Bones: By Classification of Bones: By ShapeShape

Long Long bones are bones are longer longer than they than they are wide are wide (e.g., (e.g., humerus)humerus)

Classification of Bones: Classification of Bones: By ShapeBy Shape

Flat bones Flat bones are thin, are thin, flattened, flattened, and a bit and a bit curved curved (e.g., (e.g., sternum, sternum, and most and most skull bones)skull bones)

Classification of Bones: By Classification of Bones: By ShapeShape

Irregular Irregular bones – bones – bones with bones with complicatecomplicated shapes d shapes

(e.g., (e.g., vertebrae vertebrae and hip and hip bones)bones)

Function of BonesFunction of Bones Support Support form the framework that supports the form the framework that supports the

body and cradles soft organsbody and cradles soft organs Protection – provide a protective case for Protection – provide a protective case for

the brain, spinal cord, and vital organsthe brain, spinal cord, and vital organs Movement – provide levers for musclesMovement – provide levers for muscles Mineral storage – reservoir for minerals, Mineral storage – reservoir for minerals,

especially calcium and phosphorusespecially calcium and phosphorus Blood cell formation – hematopoiesis Blood cell formation – hematopoiesis

occurs within the marrow cavities of bonesoccurs within the marrow cavities of bones

Gross Anatomy of Bones: Gross Anatomy of Bones: Bone TexturesBone Textures

Compact bone – Compact bone – dense outer layerdense outer layer

Spongy bone – Spongy bone – honeycomb of honeycomb of trabeculae filled trabeculae filled with yellow bone with yellow bone marrowmarrow

Structure of Long BoneStructure of Long Bone

Figure 6.3


Long bones consist of a diaphysis Long bones consist of a diaphysis and an epiphysisand an epiphysis

DiaphysisDiaphysis Tubular shaft that forms the axis of long Tubular shaft that forms the axis of long

bonesbones Composed of compact bone that Composed of compact bone that

surrounds the medullary cavitysurrounds the medullary cavity Yellow bone marrow (fat) is contained in Yellow bone marrow (fat) is contained in

the medullary cavitythe medullary cavity


EpiphysesEpiphyses Expanded ends of long bonesExpanded ends of long bones Exterior is compact bone, and the Exterior is compact bone, and the

interior is spongy boneinterior is spongy bone Joint surface is covered with articular Joint surface is covered with articular

(hyaline) cartilage(hyaline) cartilage Epiphyseal line separates the diaphysis Epiphyseal line separates the diaphysis

from the epiphysesfrom the epiphyses


Figure 6.3

Bone MembranesBone Membranes Periosteum – double-layered protective Periosteum – double-layered protective

membranemembrane Outer fibrous layer is dense regular Outer fibrous layer is dense regular

connective tissueconnective tissue Inner osteogenic layer is composed of Inner osteogenic layer is composed of

osteoblasts and osteoclastsosteoblasts and osteoclasts Richly supplied with nerve fibers, blood, Richly supplied with nerve fibers, blood,

and lymphatic vessels, which enter the and lymphatic vessels, which enter the bone via nutrient foraminabone via nutrient foramina

Secured to underlying bone by Sharpey’s Secured to underlying bone by Sharpey’s fibersfibers

Endosteum – delicate membrane Endosteum – delicate membrane covering internal surfaces of bonecovering internal surfaces of bone

Structure of a Flat BoneStructure of a Flat Bone

Structure of Short, Structure of Short, Irregular, and Flat BonesIrregular, and Flat Bones

Thin plates of periosteum-covered Thin plates of periosteum-covered compact bone on the outside with compact bone on the outside with endosteum-covered spongy bone endosteum-covered spongy bone (diploë) on the inside(diploë) on the inside

Have no diaphysis or epiphysesHave no diaphysis or epiphyses Contain bone marrow between the Contain bone marrow between the

trabeculaetrabeculae

Location of Location of Hematopoietic Tissue Hematopoietic Tissue

(Red Marrow)(Red Marrow)

In infantsIn infants Found in the medullary cavity and all Found in the medullary cavity and all

areas of spongy bone areas of spongy bone In adultsIn adults

Found in the diploë of flat bones, and Found in the diploë of flat bones, and the head of the femur and humerusthe head of the femur and humerus

Microscopic Structure of Microscopic Structure of Bone: Compact BoneBone: Compact Bone

Cells of BoneCells of Bone

Osteoblasts – bone-forming cellsOsteoblasts – bone-forming cells Osteocytes – mature bone cellsOsteocytes – mature bone cells Osteoclasts – large cells that resorb Osteoclasts – large cells that resorb

or break down bone matrixor break down bone matrix

Chemical Composition of Chemical Composition of Bone: OrganicBone: Organic

Osteoid – unmineralized bone matrix Osteoid – unmineralized bone matrix composed of proteoglycans, composed of proteoglycans, glycoproteins, and collagenglycoproteins, and collagen

Chemical Composition of Chemical Composition of Bone: InorganicBone: Inorganic

Hydroxyapatites, or mineral saltsHydroxyapatites, or mineral salts Sixty-five percent of bone by massSixty-five percent of bone by mass Mainly calcium phosphatesMainly calcium phosphates Responsible for bone hardness and its Responsible for bone hardness and its

resistance to compressionresistance to compression

Developmental Aspects Developmental Aspects of Bonesof Bones

Mesoderm gives rise to embryonic Mesoderm gives rise to embryonic mesenchymal cells, which produce mesenchymal cells, which produce membranes and cartilages that form the membranes and cartilages that form the embryonic skeletonembryonic skeleton

The embryonic skeleton ossifies in a The embryonic skeleton ossifies in a predictable timetable that allows fetal age predictable timetable that allows fetal age to be easily determined from sonogramsto be easily determined from sonograms

At birth, most long bones are well ossified At birth, most long bones are well ossified (except for their epiphyses)(except for their epiphyses)

Developmental Aspects Developmental Aspects of Bonesof Bones

By age 25, nearly all bones are By age 25, nearly all bones are completely ossifiedcompletely ossified

In old age, bone resorption In old age, bone resorption predominatespredominates

A single gene that codes for vitamin A single gene that codes for vitamin D docking determines both the D docking determines both the tendency to accumulate bone mass tendency to accumulate bone mass early in life, and the risk for early in life, and the risk for osteoporosis later in lifeosteoporosis later in life

Formation of BoneFormation of Bone

Intramembranous ossification – bone Intramembranous ossification – bone develops from a fibrous membranedevelops from a fibrous membrane Formation of most of the flat bones of the skull Formation of most of the flat bones of the skull

and the claviclesand the clavicles Endochondral ossification – bone forms by Endochondral ossification – bone forms by

replacing hyaline cartilagereplacing hyaline cartilage Uses hyaline cartilage “bones” as models for Uses hyaline cartilage “bones” as models for

bone constructionbone construction Requires breakdown of hyaline cartilage prior Requires breakdown of hyaline cartilage prior

to ossificationto ossification

Stages of Stages of Intramembranous Intramembranous

OssificationOssification

Figure 6.7.1



Figure 6.7.2



Figure 6.7.3



Figure 6.7.4

Endochondral Endochondral OssificationOssification

Begins in the second month of Begins in the second month of developmentdevelopment

Uses hyaline cartilage “bones” as Uses hyaline cartilage “bones” as models for bone constructionmodels for bone construction

Requires breakdown of hyaline Requires breakdown of hyaline cartilage prior to ossificationcartilage prior to ossification

Formation of bone collar around hyaline cartilage model.

1 2

3

4

Cavitation of the hyaline cartilage within the cartilage model.

Invasion of internal cavities by the periosteal bud and spongy bone formation.

5 Ossification of the epiphyses; when completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages

Formation of the medullary cavity as ossification continues; appearance of secondary ossification centers in the epiphyses in preparation for stage 5.

Hyaline cartilage

Primary ossification center

Bone collar

Deteriorating cartilage matrix

Spongy bone formation

Blood vessel of periosteal bud

Secondary ossification center

Epiphyseal blood vessel

Medullary cavity

Epiphyseal plate cartilage

Spongy bone

Articular cartilage

Stages of Endochondral Stages of Endochondral OssificationOssification

Long Bone Growth and Long Bone Growth and RemodelingRemodeling

Figure 6.10

Functional Zones in Long Functional Zones in Long Bone GrowthBone Growth

Growth zone – cartilage cells undergo Growth zone – cartilage cells undergo mitosis, pushing the epiphysis away mitosis, pushing the epiphysis away from the diaphysisfrom the diaphysis

Transformation zone – older cells Transformation zone – older cells enlarge, the matrix becomes enlarge, the matrix becomes calcified, cartilage cells die, and the calcified, cartilage cells die, and the matrix begins to deterioratematrix begins to deteriorate

Osteogenic zone – new bone Osteogenic zone – new bone formation occursformation occurs

Long Bone Growth and Long Bone Growth and RemodelingRemodeling

Growth in length – cartilage Growth in length – cartilage continually grows and is replaced by continually grows and is replaced by bone as shown bone as shown

Remodeling – bone is resorbed and Remodeling – bone is resorbed and added by appositional growth as added by appositional growth as shown in the next slide shown in the next slide

Osteoblasts beneath the periosteum secrete bone matrix, forming ridges that follow the course of periosteal blood vessels.

1 2 3 4As the bony ridges enlarge and meet, the groove containing the blood vessel becomes a tunnel.

The periosteum lining the tunnel is transformed into an endosteum and the osteoblasts just deep to the tunnel endosteum secrete bone matrix, narrowing the canal.

As the osteoblasts beneath the endosteum form new lamellae, a new osteon is created. Meanwhile new circumferential lamellae are elaborated beneath the periosteum and the process is repeated, continuing to enlarge bone diameter.

Artery Periosteum Penetrating canal

Central canal of osteonPeriosteal ridge

Appositional Growth of Appositional Growth of BoneBone

During infancy and childhood, epiphyseal During infancy and childhood, epiphyseal plate activity is stimulated by growth plate activity is stimulated by growth hormonehormone

During puberty, testosterone and estrogens: During puberty, testosterone and estrogens: Initially promote adolescent growth spurtsInitially promote adolescent growth spurts Cause masculinization and feminization of Cause masculinization and feminization of

specific parts of the skeletonspecific parts of the skeleton Later induce epiphyseal plate closure, ending Later induce epiphyseal plate closure, ending

longitudinal bone growth longitudinal bone growth

Hormonal Regulation of Hormonal Regulation of Bone Growth During Bone Growth During

YouthYouth

Bone DepositionBone Deposition Occurs where bone is injured or added strength is Occurs where bone is injured or added strength is

neededneeded Requires a diet rich in protein, vitamins C, D, and A, Requires a diet rich in protein, vitamins C, D, and A,

calcium, phosphorus, magnesium, and manganesecalcium, phosphorus, magnesium, and manganese Alkaline phosphatase is essential for mineralization Alkaline phosphatase is essential for mineralization

of boneof bone Sites of new matrix deposition are revealed by the:Sites of new matrix deposition are revealed by the:

Osteoid seam – unmineralized band of bone Osteoid seam – unmineralized band of bone matrixmatrix

Calcification front – abrupt transition zone Calcification front – abrupt transition zone between the osteoid seam and the older between the osteoid seam and the older mineralized bonemineralized bone

Bone ResorptionBone Resorption

Accomplished by osteoclastsAccomplished by osteoclasts Resorption bays – grooves formed by Resorption bays – grooves formed by

osteoclasts as they break down bone matrixosteoclasts as they break down bone matrix Resorption involves osteoclast secretion of:Resorption involves osteoclast secretion of:

Lysosomal enzymes that digest organic matrixLysosomal enzymes that digest organic matrix Acids that convert calcium salts into soluble Acids that convert calcium salts into soluble

formsforms Dissolved matrix is transcytosed across the Dissolved matrix is transcytosed across the

osteoclast’s cell where it is secreted into osteoclast’s cell where it is secreted into the interstitial fluid and then into the bloodthe interstitial fluid and then into the blood

Importance of Ionic Importance of Ionic Calcium in the BodyCalcium in the Body

Calcium is necessary for:Calcium is necessary for: Transmission of nerve impulsesTransmission of nerve impulses Muscle contractionMuscle contraction Blood coagulationBlood coagulation Secretion by glands and nerve cellsSecretion by glands and nerve cells Cell divisionCell division

Control of RemodelingControl of Remodeling

Two control loops regulate bone Two control loops regulate bone remodelingremodeling Hormonal mechanism maintains calcium Hormonal mechanism maintains calcium

homeostasis in the bloodhomeostasis in the blood Mechanical and gravitational forces Mechanical and gravitational forces

acting on the skeletonacting on the skeleton

Hormonal MechanismHormonal Mechanism

Figure 6.12

Response to Mechanical Response to Mechanical StressStress

Wolff’s law – a bone grows or Wolff’s law – a bone grows or remodels in response to the forces or remodels in response to the forces or demands placed upon itdemands placed upon it

Observations supporting Wolff’s law Observations supporting Wolff’s law includeinclude Long bones are thickest midway along the Long bones are thickest midway along the

shaft (where bending stress is greatest)shaft (where bending stress is greatest) Curved bones are thickest where they are Curved bones are thickest where they are

most likely to bucklemost likely to buckle


Trabeculae form along lines of stressTrabeculae form along lines of stress Large, bony projections occur where Large, bony projections occur where

heavy, active muscles attachheavy, active muscles attach


Figure 6.13

Bone Fractures (Breaks)Bone Fractures (Breaks)

Classified by:Classified by: The position of the bone ends after The position of the bone ends after

fracturefracture The completeness of the breakThe completeness of the break The orientation of the bone to the long The orientation of the bone to the long

axisaxis Whether or not the bones ends Whether or not the bones ends

penetrate the skinpenetrate the skin

Types of Bone FracturesTypes of Bone Fractures

Nondisplaced – bone ends retain their Nondisplaced – bone ends retain their normal positionnormal position

Displaced – bone ends are out of normal Displaced – bone ends are out of normal alignmentalignment

Complete – bone is broken all the way Complete – bone is broken all the way throughthrough

Incomplete – bone is not broken all the Incomplete – bone is not broken all the way throughway through

Linear – the fracture is parallel to the long Linear – the fracture is parallel to the long axis of the boneaxis of the bone

Types of Bone FracturesTypes of Bone Fractures

Transverse – the fracture is Transverse – the fracture is perpendicular to the long axis of the perpendicular to the long axis of the bonebone

Compound (open) – bone ends Compound (open) – bone ends penetrate the skinpenetrate the skin

Simple (closed) – bone ends do not Simple (closed) – bone ends do not penetrate the skinpenetrate the skin

Common Types of Common Types of FracturesFractures

Comminuted – bone fragments into three Comminuted – bone fragments into three or more pieces; common in the elderlyor more pieces; common in the elderly

Spiral – ragged break when bone is Spiral – ragged break when bone is excessively twisted; common sports injuryexcessively twisted; common sports injury

Depressed – broken bone portion pressed Depressed – broken bone portion pressed inward; typical skull fractureinward; typical skull fracture

Compression – bone is crushed; common Compression – bone is crushed; common in porous bonesin porous bones


Epiphyseal – epiphysis separates Epiphyseal – epiphysis separates from diaphysis along epiphyseal line; from diaphysis along epiphyseal line; occurs where cartilage cells are occurs where cartilage cells are dyingdying

Greenstick – incomplete fracture Greenstick – incomplete fracture where one side of the bone breaks where one side of the bone breaks and the other side bends; common in and the other side bends; common in childrenchildren


Table 6.2.1


Table 6.2.2


Table 6.2.3

Stages in the Healing of a Bone Stages in the Healing of a Bone FractureFracture

Hematoma Hematoma formationformation Torn blood vessels Torn blood vessels

hemorrhagehemorrhage A mass of clotted A mass of clotted

blood (hematoma) blood (hematoma) forms at the forms at the fracture sitefracture site

Site becomes Site becomes swollen, painful, swollen, painful, and inflamedand inflamed

Figure 6.14.1

1

Hematoma

Hematoma formation


FibrocartilaginouFibrocartilaginous callus formss callus forms

Granulation Granulation tissue (soft tissue (soft callus) forms a callus) forms a few days after few days after the fracturethe fracture

Capillaries grow Capillaries grow into the tissue into the tissue and phagocytic and phagocytic cells begin cells begin cleaning debriscleaning debris

Figure 6.14.2

2 Fibrocartilaginous callus formation

External callus

New blood vessels

Spongy bone trabeculae

Internal callus (fibrous tissue and cartilage)


Bony callus formationBony callus formation New bone trabeculae New bone trabeculae

appear in the appear in the fibrocartilaginous callusfibrocartilaginous callus

Fibrocartilaginous callus Fibrocartilaginous callus converts into a bony converts into a bony (hard) callus(hard) callus

Bone callus begins 3-4 Bone callus begins 3-4 weeks after injury, and weeks after injury, and continues until firm union continues until firm union is formed 2-3 months is formed 2-3 months laterlater

Figure 6.14.3

3 Bony callus formation

Bony callus of spongy bone


Bone remodelingBone remodeling Excess material Excess material

on the bone shaft on the bone shaft exterior and in the exterior and in the medullary canal is medullary canal is removedremoved

Compact bone is Compact bone is laid down to laid down to reconstruct shaft reconstruct shaft wallswalls

Figure 6.14.4

4 Bone remodeling

Healing fracture

Homeostatic ImbalancesHomeostatic Imbalances

RicketsRickets Bones of children are inadequately Bones of children are inadequately

mineralized causing softened, weakened mineralized causing softened, weakened bonesbones

Bowed legs and deformities of the Bowed legs and deformities of the pelvis, skull, and rib cage are commonpelvis, skull, and rib cage are common

Caused by insufficient calcium in the Caused by insufficient calcium in the diet, or by vitamin D deficiencydiet, or by vitamin D deficiency

Homeostatic ImbalancesHomeostatic Imbalances

OsteoporosisOsteoporosis Group of diseases in which bone Group of diseases in which bone

reabsorption outpaces bone depositreabsorption outpaces bone deposit Spongy bone of the spine is most Spongy bone of the spine is most

vulnerablevulnerable Occurs most often in postmenopausal Occurs most often in postmenopausal

womenwomen Bones become so fragile that sneezing or Bones become so fragile that sneezing or

stepping off a curb can cause fracturesstepping off a curb can cause fractures

Bones The Support System and More. Skeletal Cartilage Contains no blood vessels or nerves Contains no blood vessels or nerves Surrounded by the perichondrium.

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