6 Unit 1 Chapter 6. 6 Unit 1 Support Protection Leverage- for motion Mineral Homeostasis Blood cell...

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The Skeletal SystemThe Skeletal SystemThe Skeletal SystemThe Skeletal System

Chapter 6

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Bone FunctionBone FunctionBone FunctionBone Function

• Support• Protection• Leverage- for motion• Mineral Homeostasis• Blood cell production

Hemopoiesis in red bone marrow

• Triglyceride Storage

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Types of BonesTypes of BonesTypes of BonesTypes of Bones

• Long bones- longer than widee.g. thigh, leg, arm, forearm, fingers & toes

• Short bones- almost cube shapedMost wrist & ankle bones

• Flat bones- thin & extensive surfaceE.g. Cranial bones sternum, ribs &

scapulae

• Irregular bones- don’t fit aboveE.G vertebrae and some facial bones

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Macroscopic StructureMacroscopic StructureMacroscopic StructureMacroscopic Structure

• Parts of a long bone:• Diaphysis• Epiphysis• Metaphysis• Articular cartilage• Periosteum• Medullary cavity• Endosteum

Figure 6.1aFigure 6.1a

Figure 6.1bFigure 6.1b

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Microscopic StructureMicroscopic StructureMicroscopic StructureMicroscopic Structure

• Matrix= 25% water, 25% collagen fibers, 50%

crystallized mineral salts

• Osteogenic cells- in periosteum Osteoblasts- secrete collagen fibers-Build matrix and become trapped in lacunae

• Become osteocytes- maintain bone

• Osteoclasts –formed from monocytesDigest bone matrix for Normal bone turnover

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Compact Bone StructureCompact Bone StructureCompact Bone StructureCompact Bone Structure

• few spaces, right below periosteum

• Units = osteons (Haversian system)• Central canal- blood vessels, nerves,

lymphatics• Concentric lamellae- layers of matrix• Lacunae- “lakes” contain osteocytes• Canaliculae- little canals

nutrient flow from canals and between osteocytes

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Spongy BoneSpongy BoneSpongy BoneSpongy Bone

• units containing trabeculae• spaces between trabeculae

often contain Red Marrow• No osteons but include lacunae

& canaliculae

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Bone FormationBone FormationBone FormationBone Formation

• Ossification• 1. initially in embryo & fetus• 2. Growth• 3. remodeling• 4. repair of fractures

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Bone FormationBone FormationBone FormationBone Formation

• Mesenchyme model - replaced with bone

• Intramembranous - Bone forms directly in mesenchyme layers (membrane like)

•Endochondrial - forms within hyaline cartilage developed from mesenchyme

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Intramembranous Intramembranous OssificationOssification

Intramembranous Intramembranous OssificationOssification

• Development of ossification center-Cells differentiate=> osteogenic=> osteoblastsOsteoblasts secrete organic matrix

• Calcification- cells become osteocytesIn lacunae they extend cytoplasmic processes

to each otherDeposit calcium & other mineral salts

• Formation of trabeculae- spongy boneBlood vessels grow in and red marrow is formed

• Mesenchyme=> periosteum

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Endochondrial Endochondrial OssificationOssification


• Develop a cartilage model-• Growth- chondroblasts secrete

cartilage• Perichondrium forms on surface• Internal chondrocytes in lacunae die

and form small cavities

Figure 6.3Figure 6.3

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• Ossification proceeds inward with nutrient artery from surface perichondrium

• In disintegrating cartilage osteogenic cells=> osteoblasts and create a primary ossification center

• As bone forms perichondrium => periosteum

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• First spongy bone is formed

• Osteoblasts breaks some down=>

• Center develops a cavity

• wall of diaphysis => compact bone

• Near birth, blood vessels enter epiphysis

• Secondary center is developedHyaline cartilage at end => articular

cartilage

Figure 6.4 Figure 6.4

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GrowthGrowthGrowthGrowth

• Length- chondrocytes in the epiphyseal plate divide and increase cartilage layer

• On diaphyseal side they die and are replaced by bone

• Stops during adolescence• Periosteum supports surface growth

for thickness

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Remodeling & RepairRemodeling & RepairRemodeling & RepairRemodeling & Repair

• Remodeling in response to use- resorption by osteoclasts and

deposition by osteoblasts

• Repair after a fracture• Dead tissue removed• Chondroblasts => fibrocartilage• => spongy bone by osteoblasts• => remodeled to compact bone

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Types of FracturesTypes of FracturesTypes of FracturesTypes of Fractures

• Partial- incomplete break (crack)• Complete- bone in two or more

pieces• Closed (simple)- not through

skin• Open (compound)- broken ends

break skin

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Factors Affecting GrowthFactors Affecting GrowthFactors Affecting GrowthFactors Affecting Growth

• Adequate minerals (Ca, Mg, P)• Vitamins A, C, D• Hormones

Before puberty: hGH + insulin-like growth factors

Thyroid hormone & insulin also requiredSex steroids help adolescent growth

spurt and cause closure of epiphyseal plate.

• Weight-bearing activity

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Calcium HomeostasisCalcium HomeostasisCalcium HomeostasisCalcium Homeostasis

• Blood levels of Ca2+ controlled• Negative feedback loops• Parathyroid hormone => increased

osteoclast activity + decreased loss in urine

• Calcitonin=> decreased osteoclast activity

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Exercise & Bone TissueExercise & Bone TissueExercise & Bone TissueExercise & Bone Tissue

• Bone strengthened in response to use

• Reabsorbed during disuse

• e.g. Bone loss during bed rest, fractures in cast, astronauts with no gravity

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Divisions of Skeletal Divisions of Skeletal SystemSystem

Divisions of Skeletal Divisions of Skeletal SystemSystem

• Two divisions: axial & appendicular

• Axial- around body axisE.g. head, hyoid, ribs, sternum, &

vertebrae

• Appendicular- bones of upper & lower limbs plus girdles that connect them

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Skull & Hyoid boneSkull & Hyoid boneSkull & Hyoid boneSkull & Hyoid bone

• Cranial bones:Frontal, 2 parietal, 2 temporal, occipital,

sphenoid, and ethmoid

•Facial bones:2 nasal, 2 maxillae, 2 zygomatic, mandible,

2 lacrimal, 2 paltine, 2 inferior nasal conchae, & the vomer

Figure 6.7cFigure 6.7c

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Unique Features of SkullUnique Features of SkullUnique Features of SkullUnique Features of Skull

• Sutures- immoveable joint between skull bonesCoronal, sagittal, lambdoidal, squamous

• Paranasal sinuses-cavitiesLocated in bones near nasal cavity

• Fontanels- soft spot in fetal skullAllow deformation at birthCalcify to form sutures

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VertebraeVertebraeVertebraeVertebrae

• Encloses spinal cord• Supports head• Point of attachment for muscles

of back, ribs and pelvic girdle• 7 cervical• 12 thoracic• 1 sacrum & 1 coccyx

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Normal Curves in ColumnNormal Curves in ColumnNormal Curves in ColumnNormal Curves in Column

• 4 normal curves• Relative to front: cervical &

lumbar curves are convex•Thoracic & sacral curves are

concave• They increase strength, help in

balance and absorb shocks

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Structure of VertebraStructure of VertebraStructure of VertebraStructure of Vertebra

• Body- disc-shaped front part• Vertebral arch- extends back from body

creates with the body a hole called vertebral foramen

• 7 processes-Transverse process extending laterally on

each sideSpinous process extending dorsallyTwo each of Superior and inferior articular

processes- attach to neighboring vertebrae

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Cervical AreaCervical AreaCervical AreaCervical Area

• region is number from top to bottom

• Cervical (C1-C7)Spinous process often bifid and have transverse

foramina on transverse process

• C1- specialized to support head- called the atlas- articulates with headLacks body and spinous process

• C2 – axis- has body & spinous processAlso dens- that creates a pivot for head rotation

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Other VertebraeOther VertebraeOther VertebraeOther Vertebrae

• Thoracic (T1-T12 )Larger than cervicalHave facets for articulating with ribs

• Lumbar (L1-L5)Largest & strongest. Processes short &

thick

• Sacrum (S1-S5 fused to one unit)Foundation for pelvic girdleContain sacral foramina for nerves and

blood vessels

• Coccyx- 4 fused coccygeal vertebrae

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ThoraxThoraxThoraxThorax

• Thoracic cage = Sternum, costal cartilages & ribs and bodies of T1-T12

• Sternum- form by 3 bones that fuse by age ~25yrs= manubrium, body, xiphoid process

• Ribs- 12 pairs • 1-7 articulate with sternum directly

costal cartilage= true ribs

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Pectoral GirdlePectoral GirdlePectoral GirdlePectoral Girdle

• Attach bones of upper limbs to axial skeleton

• Right & left Clavicle & Scapula

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Upper LimbUpper LimbUpper LimbUpper Limb

• Humerus = arm bone

• Articulates with scapula at shoulder

• Articulates with radius & ulna at elbow

• Ulna – medial bone

• Radius- lateral bone (thumb side)

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Wrist & HandWrist & HandWrist & HandWrist & Hand

• Carpus (wrist) -8 bones

• Metacarpals – 5 bones of handNumber 1-5 starting with thumb

• Phalanges- 14 bones of fingersNumbered like metacarpalseach finger but the thumb has

proximal, medial & distal Thumb only proximal & distal

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Pelvic GirdlePelvic GirdlePelvic GirdlePelvic Girdle

• Pelvic girdle includes two hip bones Joined in front at pubic symphysisAt back- attached to sacrum =

sacroiliac joint

• Pelvic (hip) bone also called coxal bones

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Parts of Coxal BonesParts of Coxal BonesParts of Coxal BonesParts of Coxal Bones

• 3 bones fuse by age 23 to form coxal

• Ilium- largest & most superior

• Ischium- lower posterior part

• Pubis lower anterior part

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Lower LimbLower LimbLower LimbLower Limb

• Femur- thigh boneArticulates with hip proximally andthe tibia and fibula distally

• Patella = kneecap in front of knee joint

• Tibia- large medial, weight bearing bone of leg

• Fibula- lateral to tibia and smaller

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Ankle & FootAnkle & FootAnkle & FootAnkle & Foot

• Tarsus (ankle) has 7 bonesLarge talus (ankle bone) andCalcaneus (heel bone)

• Metatarsals (foot bones)Numbered from medial to lateral

• Phalanges (toe bones)Big toe has proximal and distal phalanges

while others have proximal, medial and distal phalanges. Numbered like metatarsals

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Male & Female Male & Female DifferencesDifferences

Male & Female Male & Female DifferencesDifferences

• Males usually have heavier bones

• Related to muscle size & strength

• Female pelvis is wider and shallower than the males- allows for birth

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Aging & Skeletal SystemAging & Skeletal SystemAging & Skeletal SystemAging & Skeletal System

• Birth through adolescence more bone formed than lost

• Young adults- gain & loss about equal

• As levels of sex steroids decline with age: bone resorption > bone formation

• Bones become brittle and lose Calcium

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