FUNCTION(S) OF THE SKELETAL SYSTEM

• Support• Protection• Movement• Mineral storage• Formation of blood

cellsHematopoiesis

CLASSIFICATION OF BONES

• Types of Osseous Tissue– Compact (dense) Bone– Spongy (cancellous) Bone

compact bone

spongy bone

TYPES OF OSSEOUS TISSUE

Long BonesA shaft with two widened

endsCompact and spongy bone

Examples:HumerusRadius & ulnaFemurTibia & fibulaPhalanges

Femur

Short BonesCube-shaped bonesMostly spongy bone

Examples:Wrist and ankle bones

Sesamoid bonesShort bones embedded

with a tendonExample: Patella

Tarsal

Patella

TYPES OF OSSEOUS TISSUE

Flat BonesThin, flat bonesLayer of spongy bone between layers of compact bone Examples:

SternumRibsSkull Parietal

TYPES OF OSSEUS TISSUE

Irregular BonesIrregular shapeMostly spongy bone

Examples:VertebraeHip bones

Vertebra

TYPES OF OSSEOUS TISSUE

DiaphysisShaft of boneCompact bone

surrounds medullary cavity

Contains yellow marrow (fat)

medullary cavity

BONE STRUCTURE

EpiphysesWidened end of long

bonesSpongy bone May contain red marrowEpipheseal line or plate

Bone growth during childhoodActively mitotic plate of hyaline cartilage

Articular cartilage covers joint surface

proximal epiphysis

distal epiphysis

BONE STRUCTURE

Bone MembranesPeriosteum

Outer C.T. membrane Inner surface may

contain osteoblasts or osteoclasts

Blood vessels and nerves

periosteum

BONE STRUCTURE

Bone MembranesEndosteum

Inner C.T. membrane Lines marrow cavities,

Haversian canals and covers trabeculae

Contains osteoblasts and osteoclasts

endosteum

BONE STRUCTURE

Red Bone MarrowFound in spongy boneHematopoietic tissueFound in:

Head of femur and humerus

Sternum and hip bones in adults

Spongy bone

spaces containing red bone marrow

BONE MARROW

Yellow Bone MarrowComposed of fatFound in:

Medullary cavityMay convert to red marrow

yellow bone marrow

BONE MARROW

Haversian canals

lacuna canaliculi

concentric lamella

Volkmann’s canal

BONE HISTOLOGY: Compact Bone

Haversian Systems (Osteons)Lamellae

Concentric, interstitial & circumferentialHaversian canalsVolkmann's canalsOsteocytes within lacunaeCanaliculi

BONE HISTOLOGY: Compact Bone

Volkmann’s canal

Haversian canal

BONE HISTOLOGY: Osteon

Spongy BoneNo osteonsScattered trabeculae

for supportCalled diploe in flat

bones Red marrow between

trabeculae

diploe

BONE HISTOLOGY: Spongy Bone

Organic Components1/3 of matrixIncludes all 3 cell typesOsteoblasts secrete osteoid =

Organic bone matrix

Inorganic Components2/3 of matrixAccounts for bone hardnessHydroxyapatites [Ca10(PO4)6(OH)2]

Mineral salts of calcium phosphate

CHEMICAL COMPOSITION OF BONE

Structures on the external surface of bone

Caused by:Muscle or ligament attachmentsBlood vessels, nerves etc. travel

Be familiar with the types of markings found on bones (see Table 6.1 in your textbook or the list in your lab notebook)

BONE MARKINGS

OsteogenesisProcess of bone formationUsed for:

Formation of bony skeleton in embryos

Bone growth during childhood and early adulthood

Bone remodeling and repair in adults

OSTEOGENESIS/OSSIFICATION

Two Types of Bone FormationIntramembranous Ossification

Bone develops from a fibrous membraneEndochondral Ossification

Bone develops from a hyaline cartilage model

OSTEOGENESIS/OSSIFICATION

Intramembranous Ossification

Used for formation of flat bones (skull & clavicles)Steps

Formation of bone matrix within fibrous membrane

· Initial ossification sight ( 8 wks) A fibrous C.T. membrane

· Ossification center appears in the C.T. membrane· Osteoid secreted by osteoblasts· Osteoid becomes mineralized

Formation of woven bone · Network of bony trabeculae forms = woven bone

Formation of compact bone plates· Trabeculae thicken at the edge, forming compact

bone· Spongy bone remains in the center

INTRAMEMBRANOUS OSSIFICATION

hyaline cartilage

perichondrium

deteriorating cartilage matrixperiosteum

ENDOCHONDRAL OSSIFICATION

Used for formation of most bones of the skeleton (2nd month)Steps

Formation of bone collar around hyaline cartilage model

· Perichondrium around hyaline cartilage model converted to periosteum

· Osteoblasts secrete osteoid onto the external shaft of the “hyaline” bone

Deterioration of cartilage matrix · Matrix within the hyaline shaft deteriorates

ENDOCHONDRAL OSSIFICATION

open spaces forming bone

blood vessel periosteal

bud

medullary cavity

secondary ossification center

epiphyseal plate

articular cartilage

ENDOCHONDRAL OSSIFICATION

Steps Formation of spongy bone by periosteal bud

· Periosteal bud invades the internal cavity Contains blood vessels and osteoblasts

· Osteoblasts produce trabeculae of bone Formation of medullary cavity

· Osteoclasts break down new bone forming a medullary cavity

Ossification of epiphyses· Secondary ossification centers form in

epiphyses shortly before or after birth· Spongy bone forms· Hyaline cartilage remains only at the

epiphyseal plate and articular surfaces

ENDOCHONDRAL OSSIFICATION

Growing Bone Adult Bone

Growth in Length

• Cartilage growth in epiphyseal plate

• Cartilage replaced by bone

• Bone remodeled

• Bone resorption

BONE GROWTH IN LONG BONES

Long bones lengthen by growth of the epiphyseal platesHarden at the end of puberty

All bones grow in width or change shape by appositional growth

BONE GROWTH IN LONG BONES

Growth in the Epiphyseal PlateHyaline plate contains dividing

chondrocytesChondrocytes enlarge

Pushed towards diaphysisEventually die

Osteoblasts secrete bone matrixForm small bone spicules

BONE GROWTH IN LONG BONES

Growth in the Epiphyseal Plate (cont.)Epiphyseal plate activity stimulated by

growth hormone during childhoodSex hormones (testosterone & estrogen)

Adolescent growth spurtEnd of adolescence

Epiphyseal plate replaced by boneLongitudinal bone growth ends

BONE GROWTH IN LONG BONES

Appositional GrowthUsed to widen bones for remodelingOsteoblasts on the periosteum:

Form new Haversian systems on outer bone surface

Increase thickness of compact boneOsteoclasts on the endosteum

Resorb boneEnlarge medullary cavity

BONE GROWTH IN LONG BONES

Growing Bone Adult Bone

Appositional Growth

• Bone addition• Bone resorption

BONE GROWTH IN LONG BONES

Bone RemodelingBone deposited and resorbed daily at the periosteal and endosteal surfaces5 to 7% of bone mass recycled weeklyRate of resorption should = rate of depositResponse to blood calcium levels

Ca2+ ions are needed for nerve impulse transmission, muscle contractions, blood coagulation

Vitamin D enhances absorption of Ca2+ from the intestine

When remodeling occurs is determined by mechanical and gravitational forces

Heavier bone usage heavier bones Nonuse bone wasting

BONE REMODELING & REPAIR

Bone DepositOsteoblasts deposit osteoid which is

later mineralized into hard boneHormonal Control

Calcitonin Produced by “C” cells in the thyroid

glands Secreted when blood Ca2+ levels Inhibits bone resorption, enhances Ca2+

deposit in bone matrix

BONE REMODELING & REPAIR

Bone ResorptionOsteoclasts secrete enzymes

Digest organic matrixOsteoclasts secrete acids

Make calcium salts more solubleMinerals freed from bone are put into bloodstream

Hormonal Control Parathyroid Hormone (PTH)

Produced by the parathyroid glands Secreted in response to low blood Ca2+

levels Stimulates bone resorption

BONE REMODELING & REPAIR

PTH promotes Ca2+ release into the blood

PTH promotes Ca2+ reabsorption from urine

Ca2+ lost in the urine

KIDNEY

BONE

SMALL INTESTINE

PTH promotes Vitamin D formation

Ingested Ca2+

BLOOD

Vitamin D promotes Ca2+ absorption

Unabsorbed Ca2+ lost in feces

Ca2+ removed from blood by osteoblasts

CALCIUM HOMEOSTASIS: PTH CONTROL

FractureBreak in the bone

Fracture TypesSimpleCompoundComminutedCompressionDepressionImpactedSpiralGreenstick

FRACTURES

greenstick fracture fissured fracture comminuted fracture

transverse fracture oblique fracture spiral fracture

TYPES OF FRACTURES

Phases of RepairHematoma Formation

Blood clot forms

hematoma

FRACTURE REPAIR

Phases of RepairFibrocartilaginous

Callus FormationFibroblasts secrete

collagenCondroblasts

secrete cartilage matrix

Osteoblasts form spongy bone

fibrocartilage

spongy bone

FRACTURE REPAIR

Phases of RepairBony Callus Formation

Osteoclasts and osteoblasts convert callus into a bony callus

bony callus

FRACTURE REPAIR

Phases of RepairBony Callus Remodeling

Continues for several months

compact bone

FRACTURE REPAIR

OsteoporosisA group of diseases in which bone

resorption exceeds bone deposit = reduction in bone mass

Vertebrae and neck of femur most susceptible

Most common in postmenapausal women due to estrogen reduction

BONE IMBALANCES

OsteoporosisRisk Factors

Insufficient exercisePoor calcium or protein intake in dietVitamin D or calcitonin metabolism

problemsSmokingDrinking Immobility

BONE IMBALANCES

OsteomalaciaDisorders in which bone is inadequately

mineralizedOsteoid is deposited but calcium salts are

notWeight-bearing bones fracture, bend or

deformRickets may occur in children with

insufficient calcium or Vitamin D intake Causes bowed legs and deformities of the

pelvis

BONE IMBALANCES

Paget’s DiseaseCharacterized by excessive, abnormal

bone formation and resorptionBone produced contains a high ratio of

woven bone to compact boneBone mineralization is reducedBones become soft and weak

BONE IMBALANCES