Skeletal System
Supportive text for this material is in
Kardong pgs.
145-152
&
177-186
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make sure you know the vocabulary
Skeletal System
Functions:
• Support
What types of animals
DON’T have osseous skeletons?
• Protection List some examples of organs
protected…
• Movement Do all movements rely on skeletal
system?
• Storage What types of elements are most likely
stored in bone?
• Blood cell What does the skeletal system have to do
production with blood cells?
http://www.art.net/~rebecca/LifeDrawing2.html
What components comprise the skeletal system?
Bones
Cartilage
Ligaments
Tendons
http://www.art.net/~rebecca/LifeDrawing2.html
Are bones dead?
How does cartilage relate to the skeletal
system?!?
Origin, growth
and repair depend
on hyaline
cartilage!
Chondroblasts
Chondrocytes
Lacunae
Perichondrium
Fibroblasts
Blood vessels
Mary, Mary quite contrary how does your
cartilage grow?!? Appositional growth
Cartilage growth
occurs in 2 regions…
1) Periphery via
perichondrial cell
division and matrix
deposition
2) Internally via
chondrocyte
division and
matrix deposition
Interstitial growth
Take 5!!!
Explain why damaged cartilage
takes a long time to heal. Why
doesn’t articular cartilage have a
perichondrium, blood vessels, or
nerves?
Discuss with your
neighbor and predict
an answer.
What are the anatomical structures
of long bones?
Consist of 2 primary
regions
Epiphyses The ends of longs bones,
primarily cancellous bone
Diaphysis The shaft of long bones,
primarily compact bone
What are the anatomical structures
of long bones?
Cartilage (hyaline)
plate between 2
regions plays
special role!!!
Epiphyseal plate
The cartilage grows
and becomes osseous
tissue.
Why wouldn’t
you want
growth here as
an adult?
What are the anatomical structures
of long bones?
What is a good
term for the
membrane
Periosteum
“around” the
2 layers, contains blood
“bone” ?
vessels & nerves
Endosteum
Single layer of cells lining medullary
cavity and cancellous spaces
What are the anatomical structures
of long bones?
Marrow
Types:
Red Site of blood cell formation
Yellow Mostly lipids, energy storage
Distribution:
Flat bones Location of red marrow
Long bones Location of yellow
marrow
What are the anatomical features of
flat, short and irregular bones?
Flat
“Cancellous sandwich”
no “dia” or “epi”
physes
Short
Would you expect
diaphysis?
Irregular
No diaphysis, small epiphyses possible
What are the histological features of bone?
Looking at this tissue…
it is mostly matrix
Mostly (65%) inorganic
Hydroxyapatite
~ Ca10(PO4)6(OH)2
Organics are collagen
and proteoglycans
(35%)
What are the histological features of bone?
Of the 2
components:
fibers (=1)
vs.
Crystals (=2)
Which type are
missing from
these bone A?
Which type are
missing from
B?
Normal long bone
A
No collagen
No minerals
B
What are the histological features of bone?
Types of bone cells:
(Most likely to have “osteo”)
Osteogenic
Cells from endosteum
and inner periosteum
Osteoblasts
Cells forming matrix
Osteocytes
Cells “trapped” in matrix
Osteoclasts
Multinucleated cells “remodel” matrix
Stem Cells
Osteochondral
progenitor cells
What are the other categories of bone besides the
shapes (ex. Long, irregular etc.)?
Bone is classified depending on
the arrangement of cells and
matrix.
Types:
Woven ~ Collagen fibers are randomly
arranged
Lamellar ~ Collagen fibers are arranged parallel
What are the other categories of bone besides the
shapes (ex. Long, irregular etc.)?
Types:
Cancellous (spongy)
~ Network of
mineralized bone
(Trabeculae) with many
spaces
~ Marrow fills up these
spaces in life
Types:
Cancellous (spongy)
Referring back to our
discussion of striae and
collagen fibers, what
direction do you
suppose the trabeculae
align in relation to
stress?
What are the other categories of bone besides the
shapes (ex. Long, irregular etc.)?
Types:
Compact ~ Dense
lamellar bone that is
mineralized (mature)
with numerous units
(osteons) arranged
around blood vessels
Compare this
photomicrograph to
the diagram and locate
the listed structures
Take 5!!!
Compact bone has a specialized
canal system for the transport of
nutrients and waste products.
Why isn’t such a system
necessary in cancellous bone?
Why not hyaline cartilage?
Discuss with your
neighbor and predict
an answer.
How does your bone grow?
2 patterns of
ossification:
Intramembranously Originally connective tissue
membrane
Endochondrally Originally cartilage that is ossified
Note: Both types start as woven bone, which
is remodeled as it matures into lamellar bone
How does your bone grow?
Intramembranous
Ossification
• Occurs during fetal
development and “finishes” by
2 years of age
• Woven bone fibers connect
and thicken forming trabeculae
(cancellous bone)
• Outer layer of osteoblasts
create outer layer of compact
bone
fontanels
How does your bone grow?
Endochondral
Ossification
• Occurs during fetal
development and “finishes” by
“20-something”
• Hyaline cartilage model formed
• Presence of blood vessels on
periphery stimulates
osteochondral progenitor cells to
become “osteos” rather than
“chondros”
• Internal chondrocytes die and
are replaced by vessels and osteo
cells
How does your bone grow?
Endochondral
Ossification
• Hyaline cartilage model
formed… everything is
“chondro”
• Blood vessels invading
perichondrium stimulate
osteogenic cells to become
osteoblasts
• Perichondrium now
becomes periosteum
• New osteoblasts form
bone collar
How does your bone grow?
• Buds of connective tissue
from periosteum invade
cartilage model. Bring in
osteogenic cells.
Then what happens?
• Osteoblasts form bone as
medullary cavity enlarges
• Bone growth progresses
towards the ends
medullary cavity enlarges
How does your bone grow?
• Osteoblasts
form bone in
Secondary
ossification
center, beginning
of epiphysis
How does your bone grow?
• When bone is
mature
epiphyseal plate
is ossified and
becomes
epiphyseal line
Take 5!!!
During endochondral ossification,
calcification of cartilage results in
the death of chondrocytes. Later in
the process, ossification of the bone
matrix does not result in the death of
osteocytes. Why is this so?
Discuss with your
neighbor and predict
an answer.
How does your bone grow?
We’ve talked
about bone
growth in
length… what
about diameter?
• Appositional
deposition and
resorption
Can bone display
interstitial growth?
How does your bone grow?
How does your bone grow?
Factors affecting bone growth:
• Nutrition
Proteins Needed for organic portion of matrix
Vitamins D & C Needed for Ca absorption and Collagen
formation
• Hormones
Growth hormone Stimulates overall growth
Thyroid hormone Stimulates bone growth and
works with GH
Sex hormones
Stimulates bone growth BUT
also closure of epiphyseal plate
How does the Skeletal System regulate Ca & P?
Ca and P
homeostasis
Calcium: needed for nerve
cell action, muscle
contraction, blood clotting
and more
Phosphorus: needed
as a component of ATP,
DNA and RNA
Why are these
elements important?
How does the Skeletal System regulate Ca & P?
Ca and P
homeostasis
regulated in part
via 2 hormones:
PTH
(parathyroid hormone)
comes from
parathyroid glands
Calcitonin
minor role…
secreted by thyroid
gland
How does the Skeletal System regulate Ca & P?
PTH
+PTH = +blood Ca
via bone, intestine and
kidney activities
Calcitonin
minor role…
+Calcitonin = -blood Ca
Which “osteo” cells do you suppose this hormone
stimulates to cause a reduction in blood Ca levels?