HKIN 473
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Kim
Bryce
Lisa
Maralyn
D’Alice
Jae
Callan
Derick
Dan
Wendy
BONES
BONES -Functions of Bones
1) Support:
- framework, without bones our bodies would be in a lump or a blob
figure
-support for soft tissue
-provides structures for muscle origins and insertions to attach to
2) Protection:
-keeps internal organs safe
examples: skull protects brain
ribs protect the heart and lungs
vertebrae protect the spinal cord
-protects from fractures being worse, from continuous large forces exerted by
muscles
3) Assisting in Movement:
-muscle origins and insertions attach to bones
-when muscles contract they move the bones, thus creating movement
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4) Storage of Minerals:
-97% of the body’s calcium is stored in bones
-also is main storage for phosphorus
-releases needed minerals into the blood and distributes them
-this maintains a crucial homeostasis
5) Production of Blood Cells:
-in certain bones (ex. Pelvis, sternum, ribs, vertebrae, condyles of humerus
and femur) connective tissue called red bone marrow exists
--usually exist in spongy bone
-red bone marrow goes through a process called hemopoiesis (hemo=blood,
poiesis = making)
-red bone marrow produces
red blood cells (erythrocytes)
white blood cells (leukocytes)
platelets
6) Storage of Chemical Energy:
-as we age most of our marrow changes from red to yellow
-yellow bone marrow mainly contains adipose cells which contain
triglycerides
(fat cells for energy)
-yellow bone marrow is usually found in the medullary cavity
Types of Bones
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Long Bones
Clavicle, humerus, radius, ulna, femur.
Shaft - the diaphysis, a thick layer of compact bone surrounding bone marrow cavity.
Ends- metaphysis and epiphysis-compact bone covering spongy inner bone. Periosteum covers the outside of
bone.
Body support and provide interconnected set of levers and linkages allowing movement. Strongest when force
is on the long axis. Beam shaped to handle the bending loads.
Short Bones
Carpals of the hand, tarsals of the foot.
Consists of spongy bone with compact covering.
Role in shock absorption and force transmission
Flat Bones
Ribs, ileum, sternum, scapula.
Two layers of compact bone w spongy and marrow.
Protect internal structures and offer broad surface for muscular attachment
Irregular Bones
Skull, pelvis, vertebrae.
Spongy bone with thin compact bone exterior
Support weight, dissipate loads, protect spinal cord, aid mvmt, site for muscle attachment
Sesamoid Bones
Patella, bones in thumb, at base of 1st metatarsal
Short bone embedded in tendon or joint capsule
Alter angle of insertion of the muscle.
Strength and Stiffness
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There are 2 types of bone tissue:
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Compact bone tissue
Soft bone tissue
Compact Bone
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Contains very few spaces
Forms external layer of all
bones
Most of the diaphyses of
long bones are long bones
Resist stresses produced
by weight and movement
Osteons are aligned in the
same direction along lines
of stress
Compact Bone Continued
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In the shaft, osteons are parallel to the long axis of
the bone
As a result, the shaft resists bending or fracturing
when considerable for is applied from either end
Compact bone is thickest where stresses are
applied in relatively few directions
The lines of stress in a bone are not static
They change in response to repeated strenuous
physical activity
Osteon
Spongy Bone
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Does not contain osteons
Instead, it consists of trabeculae
 An irregular latticework of thin columns of bone
Tend to be located where bones are not heavily stressed, or
stressed from many directions
Makes up most of the bone tissue of short, flat and irregular
shaped bones
The trabeculae are precisely orientated along lines of stress
 This helps bone resist stresses and transfer force without
breaking
Spongy Bone
Load
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The skeletal system is subject to a variety of
forces as bone is loaded in different
directions
Loads: produced by weight bearing, gravity,
muscular forces and external forces
Forces applied to bone dictate the deposition
pattern of bone
Types of Load
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Compression
Tension
Shear
Bending
Torsion
Compression
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Presses ends of bone
together
Produced by muscles,
weight bearing, gravity or
external loading
Bone absorbs maximal
stress on a plane
perpendicular to the
compressive load, therefore
shortening and widening the
bone
Tension
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Applied to bony surface,
pulls and stretches bone
apart
Bone lengthens and
narrows
Source is usually muscle
tendon (pulling)
Collagen in the bone
rearranges and aligns in
line with the tensile force
Shear Forces
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Applied parallel to the surface of an object
Creates internal angular deformation
Can occur with compressive forces, tension
forces or both
Most destructive force because bone is
anisotropic
Bending Forces
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Applied to an area
having no support
offered by the structure
Causes the bone to
bend…..(obviously)
Torsional
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Twisting force creates a shear stress over the
entire bone
Magnitude of the stress increases with
distance from the axis of rotation
Bone Response
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As described by Wolff’s
law different bones and
different sections of a
bone will respond to
tension and
compression forces
differently.
Stress
Stress is a force and is categorized based on
it’s direction with respect to the cross-section
of an object.
2 types of stress
1. Normal Stress
2. Shear Stress
Normal Stress
- acts perpendicular to the cross-section of
the loaded object
Shear Stress
- acts parallel to the cross-section of the
loaded object
Stress vs. Strain
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Strain is a direct result of stress
Normal stress produces normal strain
Shear stress produces shear strain
Normal Vs. Shear Strain
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Normal Strain produces a change in length
Normal Vs. Shear Strain
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Shear Stain produces a change in angle
Bone Remodeling
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There are three major ways in which bone
structure may be changed.
1. Osteogenesis
2. Modeling
3. Remodeling
Physical Activity vs Bone Remodeling
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Bones continually undergoes remodeling to
adapt to the stresses generated by physical
activity by replacing old bone with new bone.
Ordinary activity causes microscopic cracks in
the bone, and these are dissolved and replaced
with new bone.
Remodeling allows bone to respond to changes
in mechanical forces (Wolff's law). Exercise can
increase the diameter and strength of bone;
inactivity can decrease them.
For example
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Dominant arm of professional tennis
player have thickness that are 35%
greater than the other arm.
Osteocytes
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Two main types of
cells are responsible
for bone renewal:
osteoblasts involved
in bone formation
osteoclasts involved
in bone resorption.
Osteocytes
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Bone remodeling appears to be governed by a
feedback system in which the bone cells sense
the state of strain in the bone matrix around
them and either add or remove bone as
needed to maintain the strain within normal
limits. The process or processes by which the
cells are able to sense the strain and the
important aspects of the strain field are
presently unknown.
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Bone formation and resorption
influenced by many other factors like:
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Hypergravity,
Stress,
Pressure,
Parathyroid
Vitamin D, etc.
are
Temperature,
Hormone,