Basics of the Skeletal System and · PDF fileBasics of the Skeletal System and Articulations ... enzymes to dissolve bone matrix Figure 6.7 Microscopic anatomy of compact bone. Compact

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Basics of the

Skeletal

System and

Articulations

Learn and Understand

• Skeleton is more than just bone

• Functions go beyond support

• Bone grows upon existing bone or upon existing

cartilage, bone never grows by expanding existing

bone from within

• The pattern of bone growth in the fetus aids in birth

• Bones exhibit a trade off between strength and

weight

• Many joints do not allow movement

• Synovial joints incorporate numerous adaptations

which protect them from damage even when

frequently used

Functions of Bones

Seven important functions

– Support

– Protection

– Movement

– Mineral storage

– Blood cell formation

– Triglyceride (fat) storage

– Hormone production

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Components of Skeletal System

• Bone

– Compact or cancellous

(spongy)

• Cartilage

– Hyaline

– Fibrocartilage

– Elastic

• Tendons, ligaments

Figure 6.1 The bones and cartilages of the

human skeleton.

Cartilage inexternal ear

Cartilage inintervertebraldisc

Pubicsymphysis

Meniscus(padlike cartilagein knee joint)

Articularcartilage of a joint

Costalcartilage

Articularcartilageof a joint

Cartilages innose

EpiglottisThyroidcartilageCricoidcartilage

Larynx

TracheaLung

Bones of skeleton

Axial skeleton

Appendicular skeleton

Hyaline cartilages

Elastic cartilages

Fibrocartilages

Cartilages

Respiratory tube cartilagesin neck and thorax

Hyaline Cartilage and Interstitial Growth

Interstitial Growth:

An increase in the size of a tissue by cell

division within the interior of a part or

structure that is already formed

Daughter cells

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Cells of Bone Tissue

Cell Type Location Function

Osteo-

progenitor

cells

Periosteum,

endosteum

When stimulated, divide into

osteoblasts or bone lining cells

– “osteogenic”

Osteoblasts Initially on edge

of existing

bone, then in

matrix (become

osteocytes)

Form bone by secreting matrix

components which assemble

outside of blasts and

eventually entrap them in hard

matrix

Osteocytes Lacunae of

bone matrix

Monitor and maintain bone

matrix, stimulate bone

remodeling in response to

physical stress

Osteoclasts(derived from

macrophages)

Edges of

existing bone,

temporarily

occupy an area

Summoned to an area by

osteocytes or signaling

chemicals, have ruffled border

that uses H+ and proteolytic

enzymes to dissolve bone

matrix

Figure 6.7 Microscopic anatomy of compact bone. Compact bone Spongy bone

Central(Haversian) canal

Osteon(Haversian system)

Circumferentiallamellae

Perforating (Volkmann’s) canal

Endosteum lining bony canalsand covering trabeculae

Perforating (Sharpey’s) fibers

Periosteal blood vesselPeriosteum

Lamellae

NerveVeinArtery

CanaliculiOsteocytein a lacuna

LamellaeCentralcanalLacunae

Interstitiallamella

Lacuna(with osteocyte)

Blood & Nervous Supply:

good throughout compact bone,

indirect supply to cancellous trabeculae

Figure 6.6 A single osteon.

Structuresin thecentralcanal

Artery withcapillaries

Vein

Nerve fiber

Collagenfibersrun indifferentdirections

Twistingforce

Lamellae

Structural unit of

compact bone

Hollow tubes of bone

matrix called

lamellae

• Collagen fibers in

adjacent rings run

in different

directions

– Withstands

stress – resist

twisting

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Figure 6.4c The structure of a long bone (humerus of arm).

Endosteum

Yellowbone marrow

Compact bone

Periosteum

Perforating(Sharpey’s)fibers

Nutrientarteries

Periosteum

• White, double-layered

membrane

• Covers external surfaces

except joint surfaces

• Outer fibrous layer of

dense irregular connective

tissue

– Sharpey's fibers secure to

bone matrix

• Many nerve fibers and

blood vessels

• Anchoring points for

tendons and ligaments

Figure 6.4a The structure of a long bone (humerus of arm).Articularcartilage

Spongy bone

Epiphysealline

Periosteum

Compact bone

Medullarycavity (linedby endosteum)

Proximalepiphysis

Diaphysis

Distalepiphysis

Epiphyseal line

• Remnant of

childhood bone

growth at

epiphyseal plate

Figure 6.3 Flat bones consist of a layer of spongy bone sandwiched between two thin layers of compact bone.

Spongy bone(diploë)

Compact bone

Trabeculae ofspongy bone

Spongy Bone

• Trabeculae– Align along lines of stress to

help resist it

– No osteons

– Contain irregularly arranged

lamellae and osteocytes

interconnected by canaliculi

– Capillaries in endosteum

supply nutrients

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Bone Development

• Ossification (osteogenesis)

– Process of bone tissue formation

– Formation of bony skeleton• Embryonic skeleton ossifies predictably

• Begins in 2nd month of fetal development

– Most long bones begin ossifying by 8 weeks

– Primary ossification centers by 12 weeks

• At birth, most long bones well ossified (except epiphyses)

• At age 25 ~ all bones completely ossified and skeletal growth

ceases

– Bone remodeling and repair

• Lifelong

Approximate size of a human conceptus from

fertilization to the early fetal stage

Fertilization 1-week

conceptus

3-week

embryo

(3 mm)

5-week embryo

(10 mm)

Embryo

8-week embryo

(22 mm)

12-week fetus

(90 mm)

Bone Development: Two Types of Ossification

Intramembranous

ossificationBone develops from fibrous connective

tissue membranes 1. Ossification centers appear

2. Osteoid is secreted

3. Woven bone and periosteum form

4. Lamellar bone replaces woven bone &

red marrow appears

Forms flat bones, e.g. clavicles and

cranial bones

Endochondral

ossificationBone forms by replacing cartilage

(endochondral) bones made of hyaline

cartilage

Forms most of skeleton

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Figure 6.8 Endochondral

ossification in a long bone.

Week 9

Month 3

Birth Childhood toadolescence

Hyalinecartilage

Bone collar

Primaryossificationcenter

Area ofdeterioratingcartilage matrix

Spongyboneformation

Bloodvessel ofperiostealbud

Epiphysealblood vessel

Secondaryossificationcenter

Articularcartilage

Spongybone

Epiphysealplatecartilage

Medullarycavity

Bone collarforms around thediaphysis of thehyaline cartilagemodel.

Cartilage in thecenter of thediaphysis calcifiesand then developscavities.

The periostealbud invades theinternal cavitiesand spongy boneforms.

The diaphysiselongates and amedullary cavityforms. Secondaryossificationcenters appear inthe epiphyses.

The epiphysesossify. Whencompleted, hyalinecartilage remainsonly in theepiphyseal platesand articularcartilages.

1 2 3 4 5

Lengthening of Long Bones in Childhood

and Adolescence

• Requires presence of epiphyseal cartilage

• Epiphyseal plate maintains constant thickness

– Rate of cartilage growth on one side balanced by bone replacement on other

• Concurrent remodeling of epiphyseal ends to maintain proportion

• Result of five zones within cartilage

– Resting (quiescent) zone

– Proliferation (growth) zone

– Hypertrophic zone

– Calcification zone

– Ossification (osteogenic) zone

Figure 6.10 Growth in length of a long bone occurs at the epiphyseal plate.

Resting zone

1 Proliferation zoneCartilage cells undergomitosis.

2 Hypertrophic zoneOlder cartilage cellsenlarge.

3 Calcification zoneMatrix calcifies; cartilagecells die; matrix beginsdeteriorating; bloodvessels invadecavity.

4 Ossification zoneNew bone forms.

Calcifiedcartilage spicule

Osteoblastdepositing bonematrix

Osseous tissue (bone) coveringcartilage spicules

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Growth in Length of Long Bones

• Near end of adolescence chondroblasts divide less often

• Epiphyseal plate thins then is replaced by bone

• Epiphyseal plate closure

– Bone lengthening ceases• Requires presence of cartilage

– Bone of epiphysis and diaphysis fuses

– Females – about 18 years

– Males – about 21 years

Appositional Growth: Growth in Width

• Allows lengthening bone to widen

• Occurs throughout life

• Osteoblasts beneath periosteum secrete

bone matrix on external bone

• Osteoclasts remove bone on endosteal

surface

• Usually more building up than breaking

down

Thicker, stronger bone but not too heavy

Bone Homeostasis

• Recycle 5-7% of bone mass each week

– Spongy bone replaced ~ every 3-4 years

– Compact bone replaced ~ every 10 years

• Older bone becomes more brittle

– Calcium salts crystallize

– Fractures more easily

• Consists of bone remodeling and bone repair

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Figure 6.15 Stages in the healing of a bone fracture.

Hematoma

Internalcallus(fibroustissue andcartilage)

Externalcallus

Newbloodvessels

Spongybonetrabecula

Bonycallus ofspongybone

Healedfracture

1 A hematoma forms. 2 Fibrocartilaginous

callus forms.

3 Bony callus

forms.4 Bone

remodeling

occurs.

Stages of Bone Repair

Joints (Articulations)

• Site where two or more bones meet

• Functions of joints

– Give skeleton mobility

– Hold skeleton together

• Two classifications

– Functional – based on amount of movement

• Synarthroses—immovable joints

• Amphiarthroses—slightly movable joints

• Diarthroses—freely movable joints

– Structural – based on binding materials and

presence/absence of joint cavity

• Fibrous joints

• Cartilaginous joints

• Synovial joints – has a joint cavity

Fibrous Joints

• Bones joined by dense fibrous connective

tissue

• No joint cavity

• Most synarthrotic (immovable)

– Depends on length of connective tissue fibers

• Three types:

– Sutures

– Syndesmoses

– Gomphoses

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Figure 8.1a Fibrous joints.Suture

Joint held together with very short,

interconnecting fibers, and bone edges

interlock. Found only in the skull.

Densefibrousconnectivetissue

Sutureline

• Rigid, interlocking joints

• Immovable joints for

protection of brain

• Contain short connective

tissue fibers

• Allow for growth during

youth

• In middle age, sutures

ossify and fuse

– Called Synostoses

Figure 8.1b Fibrous joints.

• Bones connected by

ligaments

• Fiber length varies so

movement varies

– Little to no movement at

inferior tibiofibular joint

– Large amount of movement

at interosseous membrane

connecting radius and ulna

• Interosseous

membrane Radioulnar Syndesmosis

Figure 8.1c Fibrous joints.

Gomphosis

“Peg in socket” fibrous joint.

Periodontal ligament holds

tooth in socket.

Socket ofalveolarprocess

Periodontalligament

Root oftooth

• Peg-in-socket joints of

teeth in alveolar sockets

• Fibrous connection is the

periodontal ligament

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Cartilaginous Joints

• Bones united by cartilage

• No joint cavity

• Not highly movable

• Two types:

– Synchondroses

– Symphyses

Synchondroses

Bones united by hyaline cartilage

Epiphysealplate (temporaryhyaline cartilagejoint)

Sternum(manubrium)

Joint between firstrib and sternum(immovable)

Bar/plate of hyaline cartilage unites bones

– Temporary epiphyseal plate joints

• Become synostoses after plate closure

– Cartilage of 1st rib with manubrium

– Many are synarthrotic

Cartilaginous Joints: Synchondroses

Symphyses

Bones united by fibrocartilage

Body of vertebra

Fibrocartilaginous intervertebral disc (sandwiched between hyaline cartilage)

Pubic symphysis

• Fibrocartilage unites bone

– Hyaline cartilage present as articular cartilage

• Strong, flexible amphiarthroses

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Synovial Joints: Six Distinguishing Features

1. Articular cartilage: hyaline cartilage

– Prevents crushing of bone ends

2. Joint (synovial) cavity

– Small, fluid-filled potential space

3. Articular (joint) capsule

– Two layers

• External Fibrous layer

– Dense irregular connective tissue

• Inner Synovial membrane

– Loose connective tissue

– Makes synovial fluid

Figure 8.3 General structure of a synovial joint.

Ligament

Joint cavity(containssynovial fluid)

Articular (hyaline)cartilage

Fibrouslayer

Synovialmembrane(secretes synovial fluid)

Articularcapsule

Periosteum


4. Synovial fluid

– Viscous, slippery filtrate of plasma and

hyaluronic acid

– Lubricates and nourishes articular cartilage

– Contains phagocytic cells to remove microbes

and debris

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5. Different types of reinforcing ligaments

– Capsular

• Thickened part of fibrous layer

– Extracapsular

• Outside the capsule

– Intracapsular

• Deep to capsule; covered by synovial membrane

6. Nerves and blood vessels

– Nerve fibers detect pain, monitor joint position

and stretch

– Capillary beds supply filtrate for synovial fluid

Other Features of Some Synovial Joints

• Fatty pads

– For cushioning between fibrous layer and

synovial membrane or bone

• Articular discs (menisci)

– Fibrocartilage separates articular surfaces to

improve "fit" of bone ends, stabilize joint, and

reduce wear and tear

Structures Associated with Synovial Joints

• Bursae

– Sacs lined with synovial membrane

• Contain synovial fluid

– Reduce friction where ligaments, muscles,

skin, tendons, or bones rub together

• Tendon Sheaths

– Elongated bursa wrapped completely around

tendon subjected to friction

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Three Stabilizing Factors at Synovial Joints

• Shapes of articular surfaces (minor role)

• Ligament number and location (limited

role)

• Muscle tendons that cross joint (most

important)

– Muscle tone keeps tendons taut

• Extremely important in reinforcing shoulder and

knee joints and arches of the foot

• Largest, most complex joint of body

• Three joints surrounded by a single joint cavity

– Femoropatellar joint

• Plane joint

• Allows gliding motion during knee flexion

– Lateral and medial tibiofemoral joints

• Femoral condyles with lateral and medial menisci of tibia

• Allow flexion, extension, and some rotation when knee partly flexed

Knee Joint

Figure 8.8c The knee joint.

Anterior view of right knee

Quadricepsfemorismuscle

Lateralpatellarretinaculum

Tibialcollateralligament

Fibula

Fibularcollateralligament

Patella

Tendon ofquadricepsfemorismuscle

Patellarligament

Medialpatellarretinaculum

Tibia

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Figure 8.8d The knee joint.

Tibia

Arcuatepoplitealligament

Obliquepoplitealligament

Bursa

Popliteusmuscle(cut)

Lateralhead ofgastrocnemiusmuscle

Articularcapsule

Medial head ofgastrocnemiusmuscle



Tendon ofsemimembranosusmuscle

Posterior view of the joint capsule, including ligaments

FemurTendon ofadductormagnus

Figure 8.8a The knee joint.

Patellar ligament

Sagittal section through the right knee joint

Anteriorcruciateligament

Posteriorcruciateligament

Tibia

Femur

Lateralmeniscus

Articularcapsule

Lateral meniscus

Synovial cavity

Infrapatellarfat pad

Subcutaneousprepatellar bursa

Patella

Suprapatellarbursa

Tendon ofquadricepsfemoris

Deep infrapatellerbursa

Figure 8.8e The knee joint.


Lateralcondyleof femurLateralmeniscus

Tibia

Fibula

Anterior view of flexed knee, showingthe cruciate ligaments (articularcapsule removed, and quadricepstendon cut and reflected distally)


Medialcondyle


Medialmeniscus

Patellarligament

Patella


Quadricepstendon

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Figure 8.8b The knee joint.

Articularcartilage on lateral tibialcondyle


Lateralmeniscus

Superior view of the right tibia in the knee joint, showingthe menisci and cruciate ligaments


Medialmeniscus

Articularcartilageon medialtibial condyle

Anterior

Anterior Knee

https://www.youtube.com/watch?feature=pl

ayer_detailpage&v=_q-Jxj5sT0g

Posterior Knee

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Optional Slides:

• Stages in bone repair that accompany a

Figure 6.15

• Structural and functional differences

between cartilage and bone

• Structural and functional differences

between cancellous bone and compact

bone

Stages of Bone Repair: HEMATOMA Forms

• Torn blood vessels hemorrhage

• Clot (hematoma) forms

• Site swollen, painful, and inflamed

Stages of Bone Repair:

Fibrocartilaginous Callus Forms

• Capillaries grow into hematoma

• Phagocytic cells clear debris

• Fibroblasts secrete collagen fibers to span break and connect broken ends

• Fibroblasts, cartilage, and osteogenic cells begin reconstruction of bone

– Create cartilage matrix of repair tissue

– Osteoblasts form spongy bone within matrix

• Mass of repair tissue called fibrocartilaginous callus

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Bony Callus Forms

• Within one week new trabeculae appear in

fibrocartilaginous callus

• Callus converted to bony (hard) callus of

spongy bone

• ~2 months later firm union forms


Bone Remodeling Occurs

• Begins during body callus formation

• Continues for several months

• Excess material on diaphysis exterior and

within medullary cavity removed

• Compact bone laid down to reconstruct

shaft walls

• Final structure resembles original because

responds to same mechanical stressors

Cartilage Characteristics Bone Characteristics

living

components

chondroblasts, chondrocytes osteogenic cells, osteoblasts, osteoclasts,

osteocytes

matrix proteinaceous:

packed collagen fibers,

proteoglycan, water

inorganic calcium hydroxyapatite and

protein:

CaPO4 – 65% (and related Ca minerals)

collagen, proteoglycan – 35%

sheath perichondrium, except articular

surfaces

periosteum, endosteum

Not at articular surfaces

growth interstitial and appositional Appositional: endochondral and

intramembranous

blood &

nervous

supply

good blood supply at perichondrium,

none within cartilage

good throughout compact bone,

indirect supply to cancellous trabeculae

types hyaline, fibrocartilage, elastic Woven (temporary) and lamellar

cancellous and compact

benefits smooth articulation surfaces,

flexible, resilient, strong but lighter

than bone

rigid strength, protection, reservoir

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Cancellous

(Trabecular, Spongy)

Compact

Trabeculae covered with endosteum,

encased in compact bone

Osteons cemented together by

interstitial lamellae – endosteum

internally, periosteum externally

Creates a network of spaces for bone

marrow

Essentially a solid mass

No direct blood supply to the bone

matrix, rich blood supply to the

marrow-containing cavities

Network of blood vessels throughout

Strong yet lighter than compact,

orientation reflects lines of stress

Strongest, densest bone available

Epiphyses of long bones, internal

portions of short, flat, and irregular

bones

Shafts of long bones, thin outer

covering of most bones

Documents

Basics of the Skeletal System and · PDF fileBasics of the Skeletal System and Articulations ... enzymes to dissolve bone matrix Figure 6.7 Microscopic anatomy of compact bone. Compact