The
Skeletal
System
Honors A&P
Do Now:

How would your life be different if you had an
exoskeleton (skeleton on the outside)?
Name the bones:
1. Frontal
2. Maxillary
3. Mandible
4. Vertebrae‘
5. Clavicle
6. Humorous
7. Sternum
8. Rib
9. Radius
10. Ulna
11. Coxal
12. Sacrum/coccyx
13. Carpals
14. Metacarpals
15. Phalanges
16. Femur
17. Patella
18. Fibula
19. Tibia
20. Tarsals
21. Metatarsals
22. phalanges
Functions
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Support
 Structural support
 Framework for attachment
Protection
 Surrounds soft tissues and organs
Storage
 Calcium and phosphate reserve
 Energy reserves (Lipids in yellow marrow)
Hemopoeisis
 Rbc, wbc, and platelet production in red marrow
Leverage for movement
 Change magnitude and direction of forces generated by skeletal
muscles
 Tendons connect muscle to bone
Classification of Bones

Long Bones
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Longer than they are wide
Ex. Limb bones
Short Bones

Cube shaped
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Sesamoid bones
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Form in tendon
Ex. patella
Flat Bones
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Ex. Carpals, tarsals
Thin and broad
Ex. Ribs, sternum, scapulae
Irregular Bones

Complex shapes

Ex. Vertebrae and hips
Features of Long Bones

Diaphysis

Central shaft

Medullary Cavity
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Compact bone

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Covers outer surface of bone w dense irregular
tissue
Inner layer osteoblasts and osteoclasts
Secured by Sharpey’s fibers (collagen)
Nutirent foramen


Network of bony rods w/ spaces
Found in epiphysis
Periosteum

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Expanded ends covered w/ articular cartilage
Epiphyseal line in adults is remnant of
epiphyseal plate
Spongy (cancellous) bone

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Dense/solid
Found in diaphysis
Epiphysis


Contains Yellow Bone marrow
Loose connective tissue
Opening in periosteum for bv, nerrves, and lymph
vessles
Endosteum

Layer of osteoblasts that lines marrow cavity
Skeletal Cartilage



Skeletal Cartilage

Consists of mostly water

Avascular, no nerves

Surrounded by perichondrium (dense
irregular) w/bv
Types

Hyaline

Most abundant

Articular cartilage , costal cartilage ,
and respiratory cartilage

Elastic

External ear & epiglottis

Fibrocartilage

Highly copmressable

Mensci & vertebral discs
Growth

Flexible matrix to accomadate mitosis

Appositional growth – from
perichondrium

Interstitial growth – from chondrocytes
within
Microscopic Features of Compact Bone
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Haversian system (aka
osteons) – arranged in
circles
Lamella – concentric
matrix tube
Haversian (central)
canal – blood vessels
and nerve fibers
Perforating canals –
connect bv of
periosteum to haversian
canal
Osteocytes reside in
lacunae
Canaliculi – connect
lacunae to central canal
Microscopic Features of Bone (cont’d)

Spongy Bone

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Trabecule (rods create network)
Cytology
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Osteogenic cells – bone stem cells
Osteoclasts – giant multinucleated
cells that secrete acids and enzymes
to dissolve bony matrix and release
Ca (osteolysis)
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Secrete lysosomal enzymes to digest organic
matrix and HCl to make Ca soluable
Phagocytic digestion
Osteoblasts – produce new bone
(osteogenesis) and promotes Ca
deposits in bone matrix
Osteocytes – mature bone cells
Chemical composition


65% mineral salts -Hydroxyapatite
Other 1/3 Osteoid - organic
components
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Cells, collagen, and ground substance
Compact Bone vs. Spongy Bone
(Ground bone)
(Cancellous bone)
Note the absence of osteons in
spongy bone
Do Now:



List 4 things in your car….
Complete the following sentence for each
item:
A ___(item)____ is like the skeletal system
because_________________
Ossification (Osteogenesis): Bone Formation

Begins at 6 weeks
(in utero)
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Composed of fibrous
membranes and
hyaline cartilage
Flexible and resilient
to accommodate
mitosis
Intramembranous
Ossification

Bone develops within
membranes of
connective tissue

Cranial bones &
clavicles
Mesenchymal cells
form fiberous
connective
membranes

Endochondrial Ossification

1.
2.
3.
4.
Bone replaces cartilage
Primary Ossification
center – infiltrated w/bv
causing mesenchymal cells
to become osteoblasts
Bone Collar forms from
osteoblasts
Chondroctyes within shaft
enlarge and calcify and
die… opening up a cavity
Periosteal bud (bv, nerves,
osteoblasts, redmarrow
elements) invades internal
cavity
1.
2.
5.
6.
osteoclasts erode calcified
matrix
osteoblasts secrete trabeculae
Diaphysis elongates – by
hyaline cartilage followed
by ossification
Epiphysis ossify from
seconday ossification
centers where spongy
bone is retained
Bone Growth

Post-natal growth of long bones
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Growth in width (thickness)
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Cells at epiphyseal plate rapidly divide pushing epiphysis away from diaphysis
Cartilage is replaced by bone on diaphysis side, and requires continues remodeling
Epiphyseal plate closure occurs at about 18 in females and 21 in males
Osteoblasts in periosteum secrete bone on external surface as osteoclasts remove bone on the
endosteal surface
Hormonal Regulation

Growh hormone stimulates growth at epiphyseal plate

Sex hormones promote gender specific development of the skeleton
Bone Homeostasis
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Remodeling

Every week recycle 5-7% of bone mass
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Bone deposit occurs at injured or stressed sites
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Spongy bone 3-4 years
Compact bone 10 years
Vit C, D,A, Ca, P, Mg, Mn are needed
Bone resorption - osteoclasts
Wolf’s Law – bone grows or remodels in
response to the demands placed on it

Long bones thickest in middle where bending stress
Bony projections where muscles attach

Inactivity (even brief) causes atrophy (degeneration)

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Prenatal Requirements
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Prenatal – minerals absorbed from mother (often loses
bone mass)

Consume Ca and P from diet

Vitamin D3 allows absorption of Ca and P
Vitamin A and C needed for osteoblast activity

Homeostasis and Mineral Storage

Calcification – deposition of
calcium salts, regulated by hormones

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99% Ca deposited in skeleton
Ca+ ions used Nervous &
Muscular System
Ca absorbed from intestine
under control of vitamin D
Ca ion conc.regulated

Parathyroid hormone (PTH)


elevate Ca levels in body fluids
(bones become weaker)
Calcitonin

depresses Ca levels in body fluids
(bones become stronger)
Injury and Repair

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Fracture – any crack or break in a bone
Healing can take from 4 months to over a year!
Fracture hemotoma – large blood clot closes injured bv
External and internal calluses – thickenings resulting
from mitotic divisions
http://www.youtube.com/watch?v=qVougiCEgH8&fe
ature=related
Classification of Fractures

Displaced (not aligned) or Non-displaced

Complete (through) or incomplete

Linear (parallel) or transverse (perp to bone)
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Compound (open sticking through skin) or simple
(closed)

Reduction – realignment of broken bone ends
Types of Fractures
Comminuted – 3 or more fragments
Compression – crushed (vertebrae)
Spiral – due to twisting (athletes)
Depression – skull
Greenstick – children (partial
break/bend)
http://www.youtube.com/watch?v=us
n8ltc1FWU&playnext=2&list=PL27A7
948A76FDD768
Aging and Skeletal System
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Reduction in bone mass occurs between ages 30 40
Women lose ~8% skeletal mass per decade
Men lose ~3% per decade
Epiphyses, vertebrae, and jaws most vulnerable
Osteoperosis – decrease in estrogen increases
osteoclast activity (so does smoking); other causes
include lack of Ca+ in diet, inactive lifestyle, and
certain medications
Bone Markings
Bone Markings