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Skeletal system includes:• Bones of the skeleton• Cartilages, ligaments and other
connective tissues that stabilize and connect
Functions of skeletal system• Support• Storage of minerals and lipids• Blood cell production• Protection• Leverage
SECTION 6-1: Introduction to the skeletal system
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Bone shapes
SECTION 6-2: Classification of Bones
• Irregular• Sesamoid• Sutural
• Long• Flat• Short
Bone Structure• Compact bone (dense)• Spongy bone (cancellous)
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Figure 6.1 Classification of Bones by Shape
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• Diaphysis• Epiphyses• Metaphysis• Articular cartilage• Marrow cavity
• Filled with red or yellow marrow
A typical long bone includes
• Articular cartlilage
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Figure 6.2 Bone Structure
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Osseous tissue
1. solid matrix- Crystals of hydroxyapatiteCa3(PO4)2+ Ca(OH)2
2. Collagen-
3. Vascular-
SECTION 6-3: Bone Histology
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4. Wrappeda. Endosteumb. Periosteum
i. fibrous layer
ii. Cellular layer(osteogenic)-
iii. Sharpey’s Fibers
SECTION 6-3: Bone Histology
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1. Osteocytes = mature bone cells-Maintain, repair bone
2. Osteoblasts= synthesize new matrix- become osteocyte
3. Osteoclasts=dissolve bone matrix-multicuncleated, differentiate from WBC
4.Osteoprogenitor =cells differentiate into osteoblasts, repair fractures
Cells in bone:
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Figure 6.3 The Histology of Compact Bone
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Figure 6.3 The Histology of Compact Bone
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• Basic unit of compact bone is an osteon• Osteocytes arranged around a central
canal• Perforating canals extend between
adjacent osteons• Spongy bone contains trabeculae
Compact bone and spongy bone
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Figure 6.4 The Structure of Osseus Tissue
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Figure 6.5 The Distribution of Forces on a Long Bone
Bones and stress• Compact bone
located where stresses are limited in direction
• Spongy bone located where stresses are weaker or multi-directional
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• Ossification = converting other tissue to bone1. Intramembranous 2. Endochondral
• Calcification = depositing calcium salts within tissues
SECTION 6-4: Bone development and growth
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Calcification
deposition of Ca++ salts w/in a tissue
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1. Intramembraneous Ossification
• Bones form w/in a thin CT membrane• Used to form flat bones (cranium,
mandible, clavicle)
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• Begins with osteoblast differentiation
• Dermal bones produced
• Begins at ossification center
Intramembranous ossification
forming bone: red
cartilage: blue
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Steps of Intramembraneous Ossification in cranium1. Mesenchymal cells form a thin CT
membrane covering brain2. Some mesenchymal cells differentiate into
osteoblasts in the center of each membrane.(Occurs 6 weeks after fertilization)
3. Osteoblasts secrete bone @ these locations(called primary centers of ossification)
4. Ossification spreads in all directions
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Steps of Intramembraneous Ossification in cranium
5. @ birth ossification is not complete, membrane remains as sutures and fontanels(soft spots)
Fetal skulls at 13-34 weeks gestation; fontanels typically close at 6 months
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Fontanelles
• indentations of fibrous membrane between bones of fetal skull
• Intramembranous ossification is not complete until 20-22 months
• anterior• posterior• sphenoid• mastoid
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Figure 6.7 Intramembranous Ossification
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• Cartilage model gradually replaced by bone at metaphysis• Increasing bone length
• Timing of epiphyseal closure differs• Appositional growth increases bone
diameter
Endochondral ossification
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Bone Growth1. Appositional- increases diameter, while medullary
cavity hollowed out
-
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Figure 6.10 Appositional Bone Growth
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Bone Growth
2. Interstitial- occurs at epiphyseal platesa. Chondroblasts produce new cells that are pushed toward epiphysisb. At the diaphysis end of plate older cartilage is converted into bone
http://www.personal.psu.edu/staff/m/b/mbt102/bisci4online/bone/bone_growth4.swf
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Figure 6.9 Bone Growth at an Epiphyseal Cartilage
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continually changing• Remodeling• Exercise• Hormone levels
• Growth hormone and thyroxine increase bone mass
• Calcitonin and PTH control blood calcium levels
SECTION 6-5: Dynamic Nature of Bone
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Figure 6.12 A Chemical Analysis of Bone
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• 99% body’s calcium in the skeleton• Calcium ion concentration maintained by
bones GI tract and kidneys• Calcitonin and PTH regulate blood calcium
levels• Calcitonin decreases blood calcium
levels• PTH increases blood calcium levels
The skeleton is a calcium reserve
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Effects on bone growth1.Growth hormone- produced by pituitary
gland; targets growth plate activitya. Excess causes giagantism
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b. Low levels cause pituitary dwarfism• normally proportioned• treatment with growth hormone
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Effects on bone growth2. Testosterone- produced by the testes
and adrenal glands in males and by the adrenal glands in females-Responsible for the growth “spurt’ at puberty-Overproduction in males causes closure of the epiphyseal line(Caution for anabolic steroid users)
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Effects on bone growth
3. Estrogen- produced by the ovaries in females; -stimulates osteoblasts
-promotes closing of the epiphyseal line -MENOPAUSE causes bone loss!!!
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Effects of aging include1. Osteopenia (inadequate ossification)
begins between ages 30 and 40, • osteoblast activity declines, while
osteoclast activity remains level, • Women lose 8% of bone mass per
decade, while men lost only 3% in the same time period
2. Osteoporosis
SECTION 6-7: Aging and the Skeletal System
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Osteoporosis
• When the loss of bone mass compromises normal function a person is diagnosed with osteoporosis.
When the loss of bone mass compromises normal function a person is diagnosed with osteoporosis
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Figure 6.16 The Effects of Osteoporosis
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Effects on bone growth4. Parathyroid hormone- produced by the
parathyroid glands in the neck-Stimulates the osteoclasts to Ca++ to be released from the bone to enter the blood-Ca++ necessary for muscles and nerves to function properly
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Figure 6.13 Factors that Alter the Concentration of Calcium Ions in Body Fluids
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Effects on bone growth5. Calcitonin- produced by the thyroid
gland- Inhibits osteoclasts so Ca++ remains in the bone , promotes ostepoblasts
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Figure 6.13 Factors that Alter the Concentration of Calcium Ions in Body Fluids
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Effects on bone growth6. Vitamin D- some is produced in the skin ;
Most is ingested in food-Necessary for the absorption of Ca++ from the intestine into the blood
• -Osteomalacia (Rickets in children)• causing softened, weakened bones• Main symptom is pain when weight is put on
the affected bone
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Bone Fractures (Breaks)
• Bone fractures are classified by:Simple(closed) vs. compound(open)
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Types of Bone Fractures• Linear
• the fracture is parallel to the long axis of the bone
• Transverse • the fracture is perpendicular to the long
axis of the bone
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Types of Bone Fractures
• Greenstick • incomplete fracture
where one side of the bone breaks and the other side bends
• common in children
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Types of Bone Fractures
• Comminuted• bone fragments into three or more pieces• common in the elderly
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Types of Bone Fractures
• Spiral• ragged break when bone is
excessively twisted• common sports injury
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Types of Bone Fractures
• Depressed• broken bone portion
pressed inward• typical skull fracture
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Types of Bone Fractures
• Compression• bone is crushed; common in
porous bones
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Types of Bone Fractures
• Epiphyseal• epiphysis separates from
diaphysis along epiphyseal line; occurs where cartilage cells are dying
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1. Fracture hematoma2. Internal and External callus3. Cartilage replaced by bone4. Osseous callus removed
Bone graft- a transplant of bone to stimulate repair
Fracture repair
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Figure 6.14 Steps in the Repair of a Fracture
Figure 6.14
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