Chapter 6

*Lecture Outline

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Chapter 6 Outline

• Cartilage

• Bone

• Classification and Anatomy of Bones

• Ossification

• Homeostasis and Bone Growth

• Bone Markings

• Aging of the Skeletal System

Intro to the Skeletal System

• An organ system with tissues that grow and change throughout life– bones– cartilages– ligaments– other supportive connective tissues

Cartilage

• Semi-rigid connective tissue– not as strong as bone, more

flexible/resilient– mature cartilage is avascular

• Cells– chondroblasts: produce matrix– chondrocytes: surrounded by matrix

• live in small spaces called lacunae

Distribution of Cartilage

Figure 6.1

Functions of Cartilage

• Support soft tissues

– airways in respiratory system

– auricle of ear

• Articulations

– smooth surfaces where bones meet

• Precursor model for bone growth

– fetal long bones

Growth of Cartilage

• Two patterns

– Interstitial growth

• from inside of the cartilage

– Appositional growth

• along outside edge of the cartilage

Interstitial Growth

• Mitosis of chondrocytes in lacunae– forms two chondrocytes per lacuna– each synthesize and secrete new

matrix– new matrix separates the cells

• Result:– larger piece of cartilage– newest cartilage inside

Figure 6.2

Appositional Growth

• Mitosis of stem cells in perichondrium– adds chondroblasts to periphery– produce matrix, become chondrocytes– forming new lacunae– adding to existing matrix

• Results:– larger piece of cartilage– newest cartilage on outside edges

Figure 6.2

Bones

• Living organs containing all four tissue types

– primarily connective tissue

– extracellular matrix is sturdy and rigid

– strengthened by calcification: minerals deposited in the matrix (main store and source of Ca++ and PO4

---)

Function of Bones

• Support

• Protection

• Movement

• Hemopoiesis

• Storage

Classifying Bones

• Long bones– greater length than width

• Short bones– nearly equal length and width

• Flat bones– thin surfaces

• Irregular bones– other/complex shapes

Classification of BonesAccording to Shape

Figure 6.3

Long Bone Anatomy

• Diaphysis– elongated, usually cylindrical, shaft

• Epiphyses– knobby, enlarged regions at ends– strengthen joints– attachment site for tendons/ligaments

• Metaphyses– between diaphysis and epiphysis– contains epiphysial (growth) plate

Long Bone Anatomy

Figure 6.4

Long Bone Anatomy

• Articular cartilage– thin layer of hyaline cartilage on epiphyses– reduces friction between articulating bones

• Medullary/marrow cavity– cylindrical space in diaphysis– usually contains yellow bone marrow

Long Bone Anatomy

Figure 6.4

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(c)

Proximalepiphysis

Metaphysis

Diaphysis

Metaphysis

Distalepiphysis

Articular cartilage

Epiphyseal line

Articular cartilage

Spongy bone(contains redbone marrow)

Epiphyseal line

Compact bone

Medullary cavity(contains yellow bonemarrow in adult)

Endosteum

Periosteum

Nutrient arterythrough nutrient foramen

Perforating fibers

Bone Coverings

• Periosteum– dense irregular connective tissue– covers external surfaces of bones

• does not cover articular cartilages– acts as anchor for blood vessels and

nerves– anchored by perforating fibers

embedded in the bone matrix

• Endosteum– covers most internal surfaces of bones

Bone Coverings

Figure 6.5

Bone Cells

• Osteoprogenitors: mesenchymal stem cells, found in endosteum and periosteum, mitotically produce more stem cells or osteoblasts

• Osteoblasts: form bone matrix• Osteocytes: reside in lacunae; maintain

matrix and communicate with osteoblasts to cause further deposit of bone matrix

• Osteoclasts: large, multinucleate cells that dissolve bone, releasing Ca++

Bone Cells

Figure 6.6

Bone Matrix

• 1/3 organic components– cells– collagen fibers– ground substance

• 2/3 inorganic components– bone salt crystals: hydroxyapatite

• calcium phosphate and hydroxide–Ca10(PO4)6(OH)2

Comparing Bone Tissues

• Compact bone

– solid and relatively dense

– external surfaces of long and flat bones

• Spongy bone

– open lattice of narrow plates: trabeculae

– internal surface of bones

Flat Bones

• Have compact and spongy (diploë) bone

Figure 6.7

Compact Bone Organization

• The basic structural and functional unit of mature compact bone is the osteon– also known as a Haversian system– cylindrical structures– parallel to the shaft of the bone

Osteon Components

• Canals– central: carries blood vessels and nerves– perforating: perpendicular connections to central

canal with blood vessels and nerves– canaliculi: between lacunae allowing metabolic

interactions between osteocytes

• Lamellae– concentric: rings of bone around central canal– circumferential: along endosteum and periosteum– interstitial: “leftover” pieces of old osteons

Osteon or Haversion System

Figure 6.8

Ossification

• The formation and development of bone– also known as osteogenesis– begins by 8th week of embryonic

development and continues into adulthood

• Two general patterns:– Intramembranous– Endochondral

Patterns of Ossification

• Intramembranous ossification– develops from mesenchyme– produces flat bones of the skull, some

facial bones, the mandible, and central portion of clavicle

• Endochondral ossification– begins with a hyaline cartilage model– produces the majority of bones in the body

Stages of Intramembranous Ossification

1. Ossification centers form within thickened regions of mesenchyme

Figure 6.10

Stages of Intramembranous Ossification

2. Osteoid (precursor to solid bone matrix) undergoes calcification

Figure 6.10

Stages of Intramembranous Ossification

3. Woven (primary) bone and surrounding periosteum form

Figure 6.10

Stages of Intramembranous Ossification

4. Lamellar (secondary) bone replaces woven bone as compact and spongy bone form

Figure 6.10

Stages of Endochondral Ossification

1. Fetal hyaline cartilage model develops

Figure 6.11

Stages of Endochondral Ossification

2. Cartilage calcifies and a periosteal bone collar forms around diaphysis

Figure 6.11

Stages of Endochondral Ossification

3. Primary ossification center forms in the diaphysis

Figure 6.11

Stages of Endochondral Ossification

4. Secondary ossification centers form in the epiphysis

Figure 6.11

Stages of Endochondral Ossification

5. Bone replaces cartilage, except the articular cartilage and epiphyseal plates

Figure 6.11

Stages of Endochondral Ossification

6. Epiphyseal plates ossify and form epiphyseal lines

Figure 6.11

The Epiphyseal Plate

• A layer of hyaline cartilage at the boundary of the epiphysis and diaphysis– site of interstitial growth (bone lengthening)– consists of five distinct microscopic zones

Figure 6.12

Zones of Epiphyseal Plate

1. Zone of resting cartilage–farthest from medullary cavity, nearest epiphysis, small chondrocytes in hyaline cartilage

Figure 6.12

Zones of Epiphyseal Plate

2. Zone of proliferating cartilage–larger chondrocytes undergoing rapid mitotic cell division, aligned like stacks of coins

Figure 6.12

Zones of Epiphyseal Plate

3. Zone of hypertrophic cartilage– chondrocytes not dividing, become enlarged

Figure 6.12

Zones of Epiphyseal Plate

4. Zone of calcified cartilage–deposited minerals kill the chondrocytes and make matrix opaque

Figure 6.12

Zones of Epiphyseal Plate

5. Zone of ossification–walls between lacunae break, forming channels that become invaded with capillaries and osteoprogenitor cells

Figure 6.12

Bone Growth

• Bone is constantly being remodeled– more dense in early adulthood, less in

older adults

• Two types of growth:– Interstitial: in length– Appositional: in diameter

Appositional Growth

Figure 6.13

Blood and Nerve Supply

Three major types of arteries and veins:• Nutrient: supply the diaphysis; nerves

usually accompany these into the shaft of the bone

• Metaphyseal: supply area between the diaphysis and tepiphysis

• Epiphyseal: supply cells in epiphyseal plate

Arterial Supply to Bone

Figure 6.14

Effects of Hormones and Vitamins on Bone

Effects of Exercise on Bone

• Mechanical stress (i.e., muscle contraction and gravity) stimulates increase in bone density by increased osteoblast activity

• Athletes who engage in these types of activities, on average, have greater bone density

Bone Fractures

Figure 6.15

Bone Fracture Classification

Bone Fracture Repair

1. A bone fracture hematoma (blood clot) occurs.

2. A fibrocartilaginous (soft) callus forms.

3. A bony (hard) callus replaces the soft callus.

4. The bone is remodeled.

Bone Fracture Repair

Figure 6.16

Anatomical Features of Bones

Figure 6.17

Bone Aging

• During aging, bone changes in two ways:– Loses ability to produce organic

matrix (mainly collagen)– loses Ca++ and other bone salts

• This can result in a condition called osteoporosis, decrease in bone density– can result in bone fractures

Normal vs. Osteoporotic Bone