Chapter 07
Lecture Outline
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7.0 Skeletal System:
Bone Structure and Function
• Skeleton, a supporting framework, and
more
• Skeletal system, dynamic living tissues
• Interacts with all other organ systems
• Continually rebuilds and remodels itself
2
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7.1 Introduction to the Skeletal System
• Components of the skeletal system
–
–
–
–
Bones of skeleton
Cartilage
Ligaments
Other CT
• Bones
– Primary organs of the skeletal system
– Rigid framework of body
– Many other functions
3
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7.1 Introduction to the Skeletal System
• Types of bone
̶ Compact bone
o
o
o
o
Dense or cortical bone
Relatively dense CT
Appears white, smooth, and solid
80% of bone mass
̶ Spongy bone
o
o
o
o
Cancellous or trabecular bone
Located internal to compact bone
Appears porous
20% of bone mass
4
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7.1 Introduction to the Skeletal System
• Cartilage
– Semirigid CT
– More flexible than bone
• Types of cartilage
– Hyaline cartilage
o Attaches ribs to sternum
o Covers ends of some bones
o Cartilage within growth plates
o Provides model for formation of most bones in body
5
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7.1 Introduction to the Skeletal System
• Types of cartilage (continued)
– Fibrocartilage
o Weight-bearing cartilage that withstands compression
o Located in
˗ Intervertebral discs
˗ Pubic symphysis
˗ Cartilage pads of knees
– Ligaments
o Anchor bone-to-bone
– Tendons
o Connect muscle to bone
6
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Distribution of
Cartilage in the
Adult and
Juvenile
Skeletons
Figure 7.1
7
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•
In what three locations of the
body do you find
fibrocartilage?
•
Compare and contrast spongy
bone and compact bone?
•
Tendons vs Ligaments
What did you
learn?
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8
7.2a General Functions
• Bones perform several basic functions
– Support and protection
– Movement
– Hemopoiesis
– Storage of mineral and energy reserves
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7.2a General Functions
• Support and protection
– Bones provide structural support
– A framework for the body
– Protect many delicate tissues
o
o
o
o
Rib cage: heart and lungs
Cranial bones: brain
Vertebrae: spinal cord
Pelvis: urinary and reproductive organs and terminal
end of GI tract
10
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7.2a General Functions
• Movement
– Bones serve as the attachment sites for
o Skeletal muscles
o Soft tissues
o Some organs
– System of levers
o Muscle contraction exerting a pull on the skeleton
– Can alter direction and magnitude of forces
generated by muscles
11
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7.2a General Functions
• Hemopoiesis
– Blood cell production
– Occurs in red bone marrow CT
– Stem cells form blood cells and platelets
12
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7.2a General Functions
• Storage of mineral and energy reserves
– Bone stores body’s reserve of calcium and phosphate
o Released from bone into blood as needed
– Calcium essential for
o Muscle contraction
o Blood clotting
o Nerve impulse transmission
– Phosphate
o ATP utilization
o Plasma membrane
– Lipids stored in yellow bone marrow of adult bones
13
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7.2b Classification of Bones
• Four classes of bone determined by shape
• Long bones
–
–
–
–
Greater in length than width
Elongated, cylindrical shaft (diaphysis)
Most common bone shape
Found in upper and lower limbs
• Short bones
– Length nearly equal to width
o E.g., carpal bones (wrist bones), tarsals (foot bones), sesamoid bones
(bones along tendons of some muscles), patella (kneecap)
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7.2b Classification of Bones
• Flat bones
–
–
–
–
Flat, thin surfaces, may be slightly curved
Provide surfaces for muscle attachment
Protect underlying soft tissues
Locations
o Roof of skull, scapulae, sternum, ribs
• Irregular bones
– Do not fit any previous category
o E.g., vertebrae, ossa coxae (hip bones), several bones in
skull (ethmoid, sphenoid, sutural bones)
15
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Classification of
Bone by Shape
Figure 7.2
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7.2c Gross Anatomy of Bones
• Regions of a long bone
– Diaphysis
o Elongated, usually cylindrical shaft
o Provides leverage and weight support
o Compact bone with thin spicules of spongy bone extending
inward
– Medullary cavity
o Hollow, cylindrical space within the diaphysis
o Contains red bone marrow in children
o Contains yellow bone marrow in adults
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7.2c Gross Anatomy of Bones
– Epiphysis
o Knobby region at each end of long bone
o Proximal epiphysis
– End of the bone closest to body trunk
o Distal epiphysis
– End farthest from trunk
o Composed of outer thin layer of compact bone and inner
region of spongy bone
o Articular cartilage
– Thin layer of hyaline cartilage that Ccovers the joint surface
– Reduces friction and Absorbs shock in moveable joints
18
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7.2c Gross Anatomy of Bones
• Regions of a long bone (continued)
– Metaphysis
o Region of mature bone between diaphysis and epiphysis
– Epiphyseal plate
o In metaphysis
o Growth plate
o Thin layer of hyaline cartilage
o Provides for lengthwise bone growth
o In adults, the epiphyseal line, is the remnant of the
epiphyseal plate
19
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Gross
Anatomy
of a Long
Bone
Figure 7.3a
20
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7.2c Gross Anatomy of Bones
Coverings and linings of bone
• Periosteum
– Tough sheath covering outer surface of bone
– Outer fibrous layer of dense irregular CT
o Protects bone from surrounding structures
o Anchors blood vessels and nerves to bone surface
o Attachment site for ligaments and tendons
– Inner cellular layer
o Includes osteoprogenitor cells, osteoblasts, osteoclasts
– Attached to bone by numerous collagen fibers
o Perforating fibers
21
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Periosteum
Figure 7.3c
22
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7.2c Gross Anatomy of Bones
Coverings and linings of bone
• Endosteum
– Covers all internal surfaces of bone within
medullary cavity
– Incomplete layer of cells
– Contains osteoprogenitor cells, osteoblasts, and
osteoclasts
23
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Endosteum
Figure 7.3b
24
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7.2c Gross Anatomy of Bones
• Gross anatomy of other bone classes
̶ Short, flat, and irregular bones differ from
long bones
o External surface composed of compact bone
o Interior composed of spongy bone
˗ Diploë—spongy bone in flat bone of skull
o No medullary cavity
25
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Flat Bones
Within the Skull
Figure 7.4
26
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7.2c Gross Anatomy of Bones
Blood supply and innervation of bone
• Blood supply
– Bone highly vascularized, e.g., in regions of spongy bone
– Vessels enter from periosteum
– Nutrient foramen
o Artery entrance and vein exit here
• Nerves that supply bone
o Accompany blood vessels through foramen
o Innervate bone, periosteum, endosteum, and marrow cavity
o Mainly sensory nerves
27
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7.2d Bone Marrow
• Red bone marrow (myeloid tissue)
– Hemopoietic (blood cell forming)
– In children
o Located in spongy bone and medullary cavity of long bones
– In adults
o Located only in selected areas of axial skeleton
˗ Skull, vertebrae, ribs, sternum, ossa coxae, proximal epiphyses of
humerus and femur
• Yellow bone marrow (fatty substance)
– Product of red bone marrow degeneration as children mature
– May convert back to red bone marrow
o During severe anemia
o Facilitates production of additional erythrocytes
28
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Red Bone Marrow
Figure 7.5
29
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Clinical View: Bone Marrow Transplant
• Red bone marrow transplant
̶ Bone marrow destroyed by radiation/chemo
̶ Abnormally functioning marrow
̶ Harvested cells injected into bloodstream of
recipient
̶ Migrate to normal locations for red bone marrow
̶ Must be “match” between donor and recipient
̶ Typically extracted from hip if surgically removed
30
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What did you
learn?
•
What type of bones have a length nearly
equal to their width?
•
What portion of bone contains the
epiphyseal plate?
•
Where is red bone marrow found in the
adult skeleton?
•
What is the process of blood cell
formation called?
•
Describe the gross anatomy of a long
bone?
•
Name several functions of bone?
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31
7.2e Microscopic Anatomy:
Bone Connective Tissue
• Cells of bone
– Four types found in bone CT
1. Osteoprogenitor cells: stem cells derived from
mesenchyme
2. Osteoblasts: synthesize osteoid
3. Osteocytes: mature bone cells
4. Osteoclasts: bone resoprtion
32
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Osteoblasts
– Abundant rough ER and Golgi apparatus
– Synthesize and secrete osteoid
o Osteoid later calcifies
– Become entrapped within the matrix and differentiate into
osteotcytes
• Osteocytes
– Maintain bone matrix
– Detect mechanical stress on bone
– Trigger deposition of new bone matrix
33
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Osteoclasts
–
–
–
–
Large, multinuclear, phagocytic cells
Derived from fused bone marrow cells
Ruffled border increases surface area exposed to bone
Located within/adjacent to a depression/pit on bone surface
o Resorption lacuna
– Involved in bone resorption
34
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Types of Cells in Bone Connective Tissue
Figure 7.6
35
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Bone matrix has organic and inorganic
components
• Organic components
– Osteoid produced by osteoblasts, contains
o Collagen protein
o Semisolid ground substance of proteoglycans and
glycoproteins
– Gives bone tensile strength by resisting stretching
– Contributes to bone flexibility
36
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Inorganic components
– Salt crystals, calcium phosphate, Ca3(PO4)2
– Interacts with calcium hydroxide
o Forms crystals, hydroxyapatite, Ca10(PO4)6(OH)2
– Other substances incorporated into crystals
o E.g., calcium carbonate, sodium, magnesium, sulfate,
flouride
– Crystals deposit around collagen fibers
– Harden matrix and account for rigidity of bones
37
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Proportion of organic and inorganic substances
– Correct proportion allows optimal functioning
– Loss of protein results in brittle bones
• Osteogenesis Imperfecta: Brittle Bone Disease
– Insufficient calcium results in soft bones
• Rickets
38
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Bone deposition
– Begins with secretion of osteoid
– Calcification occurs, deposition of hydroxyapatite
crystals
o Calcium and phosphate ions precipitate out, form crystals
– Process requires
o Vitamin D—enhances calcium absorption from GI tract
o Vitamin C—required for collagen formation
o Calcium and phosphate for calcification
39
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Bone resorption
– Bone matrix is destroyed by substances released from
osteoclasts
– Proteolytic enzymes released from lysosomes within
osteoclasts
o Chemically digest organic matrix components
– Calcium and phosphate dissolved by hydrochloric acid
– Freed calcium and phosphate ions enter the blood
– Occurs when blood calcium levels are low
40
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Clinical View: Osteitis Deformans
• Results from disruption between osteoclast and
osteoblast function
• Characterized by excessive bone resorption followed by
excessive bone deposition
• Larger osteoclasts resorb bone at higher rate
• Newly deposited bone poorly formed
• Most commonly affected bones
̶
Pelvis, skull, vertebrae, femur, tibia
• Symptoms: bone deformity and pain
41
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Compact bone vs. spongy bone
̶ Unique and differing microscopic architecture
• Compact bone
– Composed of small cylindrical structures—osteons
(Haversian systems)
o Basic functional and structural unit of mature compact
bone
o Oriented parallel to bone diaphysis
o Appears as bull’s-eye target
42
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Osteon components
– Central canal
o Cylindrical channel at center of osteon and parallel to it
o Blood vessels and nerves extend through channel
– Concentric lamellae
o Rings of bone CT
o Surround central canal
o Collagen fibers
˗ 90 degrees from previous and next lamellae
˗ Gives bone strength and resilience
43
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Osteon components (continued)
– Osteocytes
o Mature bone cells
o Found in small spaces between concentric lamellae (lacunae)
o Maintain bone matrix
– Canaliculi
o Tiny, interconnecting channels within bone CT
o Extend from each lacuna, travel through lamellae and connect to
lacunae and central canal
o House osteocyte projections that allow intercellular contact
o Allow exchange of nutrients, minerals, gases, and wastes between
blood vessels and osteocytes
44
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Microscopic
Anatomy
of a Bone
Figure 7.8
45
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Structures in long bone, not part of osteon
– Perforating canals (Volkmann) canals
o
o
o
o
Resemble central canals
Blood vessels and nerves travel through
Perpendicular to central canals
Connect central canals within different osteons
46
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Structures in long bone, not part of osteon (continued)
– Circumferential lamellae
o
o
o
o
Rings of bone
External—run immediately internal to bone periosteum
Internal—run internal to the endosteum
Both run the entire circumference of the bone
– Interstitial lamellae
o
o
o
o
Components of compact bone between osteons
Or partially resorbed osteons
Look like they have a “bite” taken out
Incomplete, no central canal
47
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Components of
Bone—Osteons
Figure 7.7a
48
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Components
of Bone—
Compact Bone
Figure 7.7b
49
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7.2e Microscopic Anatomy:
Bone Connective Tissue
• Compact bone vs. spongy bone
• Spongy bone
– Trabeculae
o Open lattice of narrow rods and plates of bones
o Bone marrow fills spaces
o Meshwork of crisscrossing bars
o Resistance to stresses
– Parallel lamellae
o Bone matrix
o Osteocytes between lamellae
o Canaliculi radiate from lacunae
50
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Components of
Bone—Trabeculae
Figure 7.7c
51
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What did you
learn?
•
What is the function of an
osteoblast? An osteoclast?
•
Which lamellae surrounds
each osteon?
•
Bone resorption or bone
deposition?
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52
7.2f Microscopic Anatomy:
Hyaline Cartilage Connective Tissue
• Structure of hyaline cartilage
– Cells scattered through matrix of protein fibers
– Embedded in a gel-like ground substance
o Includes proteoglycans but not calcium
–
–
–
–
Resilient and flexible
High percentage of water
Highly compressible and a good shock absorber
Avascular and contains no nerves
53
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7.2f Microscopic Anatomy:
Hyaline Cartilage Connective Tissue
• Structure of hyaline cartilage (continued)
– Chondroblasts—produce cartilage matrix
– Chondrocytes
o Chondroblasts encased within the matrix
o Occupy small spaces, lacunae
o Maintain the matrix
– Perichondrium
o Dense irregular CT
o Covers cartilage and helps maintain its shape
54
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55
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What did you
learn?
•
What cells secrete cartilage
matrix?
•
What cells maintain matrix?
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56
7.3 Cartilage Growth
• Process of cartilage growth
– Begins during embryologic development
– Growth in length through interstitial growth
o Occurs within internal regions of cartilage
– Growth in width by appositional growth
o Occurs on cartilage’s outside edge
57
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Formation
and Growth
of Cartilage—
Interstitial
Growth
Figure 7.9a
58
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Formation
and Growth
of Cartilage—
Appositional
Growth
Figure 7.9b
59
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7.4 Bone Formation
• Ossification (osteogenesis)
– Formation and development of bone CT
– Begins in the embryo
– Continues through childhood and adolescence
– By 8th through 12th weeks of embryonic
development
o Skeleton begins forming
˗ From intramembranous ossification
˗ Or endochondral ossification
60
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7.4a Intramembranous Ossification
• Intramembranous ossification
– Bone growth within a membrane
– Dermal ossification
– Produces
o
o
o
o
Flat bones of skull
Some of the facial bones
Mandible
Central part of the clavicle
– Begins when mesenchyme thickens with capillaries
61
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7.4a Intramembranous Ossification
• Steps of intramembranous ossification
1) Ossification centers form within thickened regions of
mesenchyme
– Some cells become osteoprogenitor cells
– Some cells become osteoblasts secreting osteoid
2) Osteoid undergoes calcification
– Calcium salts deposit onto osteoid and crystallize
– Entrapped cells become osteocytes
62
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Intramembranous Ossification
Figure 7.10
63
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7.4b Endochondral Ossification
• Endochondral ossification
– Begins with a hyaline cartilage model
– Produces most bones of skeleton, including
o Bones of upper and lower limbs, pelvis, vertebrae, ends of clavicle
– An example of this process is long bone development
• Steps of long bone development in a limb
1. Fetal hyaline cartilage model develops
– Chondroblasts secrete cartilage matrix
o During 8th to 12th week of development
64
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7.4b Endochondral Ossification
• Steps of long bone development in a limb (continued)
2. Cartilage calcifies, a periosteal bone collar forms
– Chondrocytes in the cartilage model produce holes in the
matrix
– Matrix calcifies, and chondrocytes die
o Produces calcified cartilage shaft with large holes
– Blood vessels grow toward cartilage
– Osteoblasts develop and secrete osteoid
o Form a layer of osteoid around calcified cartilage shaft
o Periosteal bone collar formed
65
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7.4b Endochondral Ossification
• Steps of long bone development in a limb (continued)
3. Primary ossification center forms in diaphysis
– Periosteal bud extends from periosteum into cartilage shaft
o Growth of capillaries and osteoblasts
– Osteoids produce osteoid on calcified cartilage template
o Primary ossification center
o First major center of bone formation
o Most formed by 12th week of development
– Bone development extends in both directions toward
epiphyses
– Bone CT displaces calcified, degenerating cartilage
66
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7.4b Endochondral Ossification
• Steps of long bone development in a limb (continued)
4. Secondary ossification centers form in epiphyses
– Hyaline cartilage calcifies and degenerates
– Blood vessels and osteoprogenitor cells enter
– Secondary ossification centers form
o Bone displaces cartilage
o Not all form at birth
– Osteoclasts resorb some bone matrix
o Creates hollow medullary cavity
67
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7.4b Endochondral Ossification
• Steps of long bone development in a limb (continued)
5. Bone replaces cartilage, except articular cartilage and
epiphyseal plates
6. Epiphyseal plates ossify and form epiphyseal lines
– Lengthwise bone growth continues into puberty
– Growth continues until epiphyseal plate is converted to
epiphyseal line
o Indicates bone has reached adult length
– Occurs between ages of 10 and 25
68
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Figure 7.11
69
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Figure 7.11
70
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7.5 Bone Growth and Bone Remodeling
• Bone growth and remodeling
– Begins during embryologic development
• Bone growth in length—interstitial growth
• Bone growth in diameter or thickness—appositional
growth
71
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7.5a Bone Growth
• Interstitial growth
– Dependent upon cartilage growth in epiphyseal plate
• Five zones of epiphyseal plate
1. Zone of resting cartilage
̶ Nearest epiphysis
̶ Small chondrocytes distributed throughout matrix
̶ Resembles mature hyaline cartilage
̶ Secures epiphysis to epiphyseal plate
72
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7.5a Bone Growth
• Five zones of epiphyseal plate (continued)
2. Zone of proliferating cartilage
̶ Chondrocytes undergo rapid mitotic division
̶ Align into longitudinal columns of flattened lacunae
̶ Columns parallel to diaphysis
3. Zone of hypertrophic cartilage
̶ Chondrocytes cease dividing
̶ Begin to hypertrophy
̶ Walls of lacunae become thin
73
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7.5a Bone Growth
• Five zones of epiphyseal plate (continued)
4. Zone of calcified cartilage
̶ Composed of 2 to 3 layers of chondrocytes
̶ Minerals are deposited between columns of lacunae
̶ Destroys chondrocytes
5. Zone of ossification
̶ Walls break down between lacunae in columns
̶ Spaces invaded by capillaries and osteoprogenitor cells
̶ New bone matrix deposited on the calcified cartilage
matrix
74
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Epiphyseal
Plate
Figure 7.12a
75
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7.5a Bone Growth
Interstitial growth (continued)
• Epiphyseal plate
–
–
–
–
Maintains thickness during childhood
At maturity, rate of cartilage production slows
Osteoblastic activity increases
Plate narrows until it disappears
o Interstitial growth stops
– Remnant is an internal thin line of compact bone
o Epiphyseal line
76
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Figure 7.12b
77
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7.5a Bone Growth
• Appositional growth
– Occurs within the periosteum
– Bone matrix deposited within layers parallel to surface
– Layers termed external circumferential lamellae
o As they increase in number, structure increases in diameter
– Osteoclasts resorb bone matrix along medullary cavity
– Transforms infant bone into a larger adult version
78
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Appositional Bone Growth
Figure 7.13
79
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Clinical View: Achondroplastic Dwarfism
• Achondroplasia
– Characterized by abnormal conversion of hyaline cartilage to
bone
– Most common, achondroplastic dwarfism
o Long bones of limbs stop growing in childhood
o Other bones continue normal growth
– Short in stature but large head
– Failure of chondrocytes in epiphyseal plate to grow and
enlarge
– Inadequate endochondral ossification
80
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7.5b Bone Remodeling
• Bone remodeling
– Continues throughout adulthood
– Occurs at periosteal and endosteal surfaces of a bone
– Occurs at different rates
o E.g., distal part of femur is replaced every 4 to 6 months
o E.g., diaphysis of femur not completely replaced over a lifetime
– 20% of skeleton replaced yearly
– Dependent upon the coordinated activities of osteoblasts,
osteocytes, and osteoclasts
– Influenced by hormones and mechanical stress
81
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7.5b Bone Remodeling
• Mechanical stress
• Increased bone mass
– From weight-bearing activities
o E.g., weight lifting, walking, or running
– Can increase total bone mass
• Decreased bone mass
– From removal of mechanical stress
– Reduced collagen formation
– Demineralization
o E.g., decreased strength of unstressed bone in immobilized fracture
82
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7.5c Hormones That Influence
Bone Growth and Remodeling
• Growth hormone
– Somatotropin produced by anterior pituitary gland
– Stimulates liver to produce hormone, somatomedin
o Both directly stimulate growth of cartilage in epiphyseal plate
• Thyroid hormone
– Secreted by thyroid gland
– Influences basal metabolic rate of bone cells
• Sex hormones
– Estrogen and testosterone
– Secreted in large amounts at puberty
o Dramatically accelerate bone growth
83
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7.5c Hormones That Influence
Bone Growth and Remodeling
• Glucocorticoids
– Released from adrenal cortex
– Regulate blood glucose level
– High amounts increase bone loss
o Impairs growth at epiphyseal plate in children
o Must monitor if child receiving high doses of glucocorticoids
(e.g., in asthma)
• Serotonin
– If levels are too high
o Osteoprogenitor cells are prevented from differentiating into
osteoblasts
o Could be linked to low bone density disorders
84
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What did you
learn?
•
What is the term for bone growth
in width? For bone growth in
length?
•
What hormone stimulates the liver
to produce somatomedin, causing
cartilage proliferation at the
epiphyseal plate?
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85
7.6 Regulating Blood Calcium Levels
• Regulating calcium concentration in blood is essential
• Calcium is required for
–
–
–
–
Initiation of muscle contraction
Exocytosis of molecules from cells, including neurons
Stimulation of the heart by pacemaker cells
Blood clotting
• Two primary hormones increase blood calcium
– Calcitriol
– Parathyroid hormone
86
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7.6b Parathyroid Hormone and Calcitriol
• Parathyroid hormone (PTH)
– Secreted and released by parathyroid glands in response to
reduced blood calcium levels
– Accelerates conversion to calcitriol by kidney
• PTH and calcitriol interact with major organs
̶
Bone CT of skeleton
o Act synergistically to increase release of calcium from the bone
into the blood
o Increase osteoclast activity
87
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7.6b Parathyroid Hormone and Calcitriol
• PTH and calcitriol interact with major organs
(continued)
– Kidneys
o Stimulate the kidney to excrete less calcium in urine
o Increasing calcium reabsorption in the kidney tubules
– Small intestine
o Only calcitriol increases absorption of calcium from small intestine
into the blood
88
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Clinical View: Rickets
• Disease caused by vitamin D deficiency in childhood
• Characterized by deficient calcification of osteoid
tissue
• Bowlegged appearance
• Disturbances in growth, hypocalcemia, and tetany
(cramps and twitches)
̶
Caused by low blood calcium
• Occurs in some developing nations
• Incidence increasing in urban U.S. children
89
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7.6c Calcitonin
• Calcitonin
– Aids in decreasing blood calcium levels
– Less significant role than PTH or calcitriol
– Released from the thyroid gland in response to high blood
calcium levels
– Also secreted in response to exercise
– Inhibits osteoclast activity
– Stimulates kidneys to increase loss of calcium in the urine
o Reducing blood calcium levels
90
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Effects of Parathyroid Hormone
and Calcitriol on Blood Calcium Levels
Figure 7.15
91
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What did you
learn?
•
What organs are involved in
activating vitamin D3 to calcitriol?
•
Parathyroid hormone and calcitriol
are secreted in response to what?
•
How does calcitonin work on bone
and kidneys to regulate blood
calcium levels?
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92
7.7 Effects of Aging
• Osteopenia
– Occurs slightly in all people with age
– Begins age 35–40
– Osteoblast activity declines; osteoclast activity at previous
levels
– Vertebrae, jaw bones, epiphyses loose large amount of
mass
– Women loose more of their skeletal mass every decade
than men
93
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7.7 Effects of Aging
• Osteoporosis
– Reduced bone mass sufficient to compromise normal
function
– Occurs in a significant percentage of older women
– Occurs in a smaller percentage of older men
• Reduced hormones with age
– Vitamin D, growth hormone, estrogen, and testosterone
– Contributes to reduction in bone mass
94
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Clinical View: Osteoporosis
• Results in decreased bone mass, weakened bones prone to
fracture
• Linked to age, onset of menopause, smoking history, Caucasian
race
• Postmenopausal women at most risk
• Increased incidence of fracture
̶ Especially at wrist, hip, vertebral column
• Best treatment is prevention with diet and physical activity in
young adults
• Medical treatments involve
̶ Slowing rate of bone loss
̶ Attempting to stimulate new bone growth
95
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7.8 Bone Fracture and Repair
• Breaks in bone
– Fractures
– Result of unusual stress or sudden impact
– Increased incidence with age
o Due to normal thinning and weakening of bone
• Types of fractures
– Stress fracture
o Thin break caused by increased physical activity
o Bone experiences repetitive loads (e.g., runners)
96
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7.8 Bone Fracture and Repair
• Types of fractures (continued)
– Pathologic fracture
o Occurs in bone weakened by disease
– Simple fracture
o Broken bone not penetrating skin
– Compound fracture
o One or both ends of the bone pierce overlying skin
97
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Figure 7.16
98
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7.8 Bone Fracture and Repair
• Four steps of bone fracture repair
1) Fracture hematoma forms from clotted blood
• Blood vessels torn within periosteum
2) Fibrocartilaginous callus forms
• Regenerated blood capillaries infiltrate hematoma
• Fracture hematoma reorganized into a CT procallus
• Fibroblasts produce collagen fibers
• Chondroblasts form dense regular CT
• Procallus becomes fibrocartilaginous (soft) callus
99
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7.8 Bone Fracture and Repair
• Four steps of bone fracture repair (continued)
3) Hard (bony) callus forms
• Osteoblasts adjacent to callus produce trabeculae
• Replaces callus
• Forms a hard (bony) callus
• Continues to grow and thicken
4) Bone is remodeled
• Final phase of fracture repair
• Osteoclasts remove excess bony material
• Compact bone replaces primary bone
• Usually leaves a slight thickening of bone
100
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Fracture Repair
Figure 7.17
101
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