Chapter 6
*Lecture Outline
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Chapter 6 Outline
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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
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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
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Two patterns
– Interstitial growth
• from inside of the cartilage
– Appositional growth
• along outside edge of the
cartilage
Interstitial Growth
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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
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Mitosis of stem cells in perichondrium
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adds chondroblasts to periphery
produce matrix, become chondrocytes
forming new lacunae
adding to existing matrix
Results:
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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
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Support
Protection
Movement
Hemopoiesis
Storage
Classifying Bones
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Long bones
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Short bones
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nearly equal length and width
Flat bones
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greater length than width
thin surfaces
Irregular bones
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other/complex shapes
Classification of Bones
According to Shape
Figure 6.3
Long Bone Anatomy
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Diaphysis
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Epiphyses
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elongated, usually cylindrical, shaft
knobby, enlarged regions at ends
strengthen joints
attachment site for tendons/ligaments
Metaphyses
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between diaphysis and epiphysis
contains epiphysial (growth) plate
Long Bone Anatomy
Figure 6.4
Long Bone Anatomy
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Articular cartilage
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thin layer of hyaline cartilage on epiphyses
reduces friction between articulating bones
Medullary/marrow cavity
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cylindrical space in diaphysis
usually contains yellow bone marrow
Long Bone Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Articular cartilage
Spongy bone
(contains red
bone marrow)
Proximal
epiphysis
Epiphyseal line
Metaphysis
Compact bone
Medullary cavity
(contains yellow bone
marrow in adult)
Endosteum
Periosteum
Perforating fibers
Diaphysis
Nutrient artery
through nutrient foramen
Metaphysis
Epiphyseal line
Figure 6.4
Distal
epiphysis
Articular cartilage
(c)
Bone Coverings
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Periosteum
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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
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covers most internal surfaces of bones
Bone Coverings
Figure 6.5
Bone Cells
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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
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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
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Canals
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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
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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
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The formation and development of bone
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also known as osteogenesis
begins by 8th week of embryonic
development and continues into adulthood
Two general patterns:
– Intramembranous
– Endochondral
Patterns of Ossification
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Intramembranous ossification
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develops from mesenchyme
produces flat bones of the skull, some
facial bones, the mandible, and central
portion of clavicle
Endochondral ossification
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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
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Bone is constantly being remodeled
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more dense in early adulthood, less in
older adults
Two types of growth:
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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
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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