WHAT DO WE MEAN BY THE SKELETAL SYSTEM?
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The skeletal system serves as the supporting
framework framework of the body.
THE
SKELETAL SYSTEM
The body shape
Mechanism of movement
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Erect posture observed in humans would be
impossible without the skeletal system.
COMPONENTS OF THE SKELETAL SYSTEM????
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Support
Protection
Attachment sites for skeletal muscles
FUNCTIONS
OF THE
SKELETAL
SYSTEM:
Blood cell production
Mineral storage
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HOW ARE THESE PORTIONS OF THE SKELETAL
SYSTEM INVOLVED IN PROTECTION???
Bones Protects and supports organs: Your skull shields your brain, your ribs
protect your heart and lungs, and your backbone protects your spine.
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BONE STRUCTURE :
Living cells
Non-living matrix
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TYPES OF BONES:
1.Long bones
2.Short bones
3.Flat bones
4.Irregular bones
Examples?????
Flat bones (e.g. skull/sternum )
Long bones (e.g. femur/radius)
Short bones (e.g. carpal/tarsals)
Irregular bones (e.g. pelvic/vertebrae)
Sesamoid bones (e.g. pisiform/patella)
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Other examples??
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Structure of a
Long Bone
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Structure
Function
Epiphysis
Articulate with adjacent bones to form joints.
Articular cartilage
Protects and cushions the end of the bone, provide a smooth surface
for movement.
Diaphysis
Each epiphysis is joined to the diaphysis by an epiphyseal plate
(immature bone) or epiphyseal line (mature bones)
Periosteum
The entire bone is covered by periosteum except the part that is
covered by the articular cartilage.
Spongy/cancellous bone
Interior of small bones, skull,& epiphysis in long bones. Consist of thin
rods of plates called trabecular that forms a mesh-like structure.
Red marrow
Spaces of the spongy bone are filled with red marrow
Compact bone
The wall of the diaphysis and a thin surface over the epiphysis
Medullary cavity
The cavity that extends the length of the diaphysis that is lined by a
thin membrane called endosteum. It is filled with fatty yellow
marrow.
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¡Why we have spongy
and compact bone?
¡Why not just one
uniform structure?
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¡ Spongy bone reduces the weight of the bone without
reducing its supportive strength. It consist of rods or plates
called trabeculae that forms a meshlike framework with
spaces.
¡ Compact bone provides the supportive strength of long
bones. It consist of tightly packed bone tissue. It lacks the
spaces found in spongy bone.
¡ This explains why we need both structures in our long bone
composition rather than one uniform structure.
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Compact
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MICROSCOPIC STRUCTURE
¡ Compact bone is composed of subunits called osteons.
¡ osteon is composed of central canal.
¡ Central canal is surrounded by layers of bone matrix called
lamellae.
¡ Lamellae has the bone cells osteocytes arranged between
its layers.
¡ What is the function of osteocytes????
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OSTEOCYTES
¡ Osteocytes derive from osteoblasts or bone-
forming cells and are essentially osteoblasts
surrounded by the products they secreted.
¡ Osteocytes are the most abundant type of cell
in mature bone tissue.
¡ The osteocyte is capable of bone deposition.
¡ The osteocyte may aid in calcium removal from
bone when the body’s calcium level drops too
low.
¡ Involved in bone remodeling. HOW??????
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BONE REMODELING BY OSTEOCYTES:
By transmitting signals to other osteocytes in response to
even slight deformations of bone caused by muscular activity.
In this way, bone becomes stronger if additional stress is
placed on it (for example, by frequent exercise or physical
exertion) and weaker if it is relieved of stress (for example,
by inactivity).
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Childhood and adolescence are critical periods in which the skeleton is most responsive
to exercise. Several evidences demonstrated that the promotion of physical exercise
during bone development maximizes the chances of accruing bone, potentially delaying
the onset of osteoporosis in later life. The response of bone tissue to mechanical stimuli is
influenced by age, hormone levels, and other metabolic factors; furthermore, it depends
on the age at start, magnitude, duration and frequency of stimuli.
CRITICAL
THINKING
How osteocytes respond in case of physically active
individuals (exercising) and in case of physically inactive
individuals???
HOW DOES
THE BONE
SURVIVE??????
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NUTRIENT FORAMEN
¡ A channel entering or passing through a bone.
¡ The blood vessels from branches that pass through the
communicating canals and enter the central canal to supply
nutrients to the bone cells.
¡ This mainly happens within the compact bone, so how does
the spongy bone survive???????
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HOW SPONGY BONE SURVIVE???
The bony plates of spongy bone
lack osteons, so bone cells
receive nutrients by diffusion of
materials through canaliculi from
blood vessels in the red marrow
surrounding the bony plates.
???????
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The process of bone formation is called
ossification.
BONE
FORMATION
It starts during the 6th or the 7th week of
embryonic life.
Bones are formed by the replacement
existing connective tissue with bone tissue.
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BONE FORMATION
There are two types of bone formation:
1.Intramembranous ossification
2.Endochondral ossification
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BONE FORMATION
Intramembranous
Endochondral
1. Membranes of embryonic connective tissue form at sites
of future bones.
1. Bone is performed in hyaline cartilage.
2. Some connective tissue cells become osteoblasts. Which
deposit spongy bone within the membrane.
2. Cartilage is calcified, and osteoblasts derived from the
periosteum form spongy bone, which replaces cartilage in
the ossification centers.
3. Osteoblasts from the enclosing membrane now called
the periosteum, deposits a layer of compact bone over the
spongy bone.
3. Osteoblasts of periosteum from a collar of compact
bone that thickens and grows toward each end of the bone.
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BONE FORMATION
¡ In both types of ossification, some primitive
connective cells are changed to become
osteoblasts.
¡ Osteoblasts deposit bone matrix around
themselves.
¡ Once this occurs, they are called osteocytes.
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osteoblasts are a type of bone cells responsible for the formation of new bones while
osteocytes are a type of bone cells that maintain the bone mass.
CRITICAL
THINKING
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SKELETAL SYSTEM PART 2
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OSSIFICATION
¡ In both types of ossification, some primitive connective
tissue cells are changed to become bone-forming cells
called osteoblasts.
¡ Intramembranous Ossification: is the direct laying
down of bone into primitive connective tissue. While,
¡ Endochondral Ossification: involves cartilage as a
precursor.
‫كمقدمة‬
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INTRAMEMBRANOUS VS ENDOCHONDRAL OSSIFICATION
¡ Intramembranous Ossification: forms the flat bones
of the skull, face, jaw, and center of clavicle. Bone is
formed in sheet-like layers that resemble a membrane.
¡ Endochondral Ossification: forms most bones in the
body, mostly long bones, and replace cartilage with bone.
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INTRAMEMBRANOUS OSSIFICATION
¡ Most skull bones are formed by intramembranous ossification.
¡ Connective tissue membranes form early in embryonic life at sites of
future intramembranous bones.
¡ Later some connective tissue cells become osteoblasts and deposit
spongy bone within the membranes.
¡ Osteoblasts from the covering membrane(periosteum) deposit a
layer of compact bone over the spongy bone.
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INTRAMEMBRANOUS OSSIFICATION
¡ Some bone tissue must be removed and re-formed in
order to produce the correct shape of the bone as it
develops and grows.
¡ WHICH CELLS ARE RESPONSSIBLE FOR THIS
FUNCTION??????
osteoclast
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INTRAMEMBRANOUS OSSIFICATION
¡ Cells that remove bone matrix are called osteoclasts. The
opposing actions of osteoblasts.
¡ Osteoclasts ultimately produce the shape of the mature
bone.
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ENDOCHONDRAL OSSIFICATION
1. Primary ossification center
2. Secondary ossification center
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ENDOCHONDRAL OSSIFICATION
¡ Most bones of the body are formed by
endochondral ossification.
¡ Future endochondral bones are performed in
hyaline cartilage early in embryonic development.
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ENDOCHONDRAL OSSIFICATION
¡ In long bones, a primary ossification center forms in the middle of
the bone.
‫عنق‬
¡ Osteoblasts from the developing periosteum form a collar of
compact bone around the ossification center.
¡ Cartilage in the primary ossification center calcifies, and the
chondrocytes die.
¡ Blood vessels and nerves penetrate into the primary ossification
center carrying along osteoblasts from the periosteum, which form
spongy bone.
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ENDOCHONDRAL OSSIFICATION
¡ In long bones, a secondary ossification center forms in each
epiphysis
¡ During this time, osteoclasts begin to remove spongy bone
in the diaphysis to form the medullary cavity.
¡ The bone will continue to grow as the ossification
progresses.
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ENDOCHONDRAL OSSIFICATION
As cartilage continues to be replaced, the cartilage
between the primary and the secondary
ossification centers decreases until only a thin
plate of cartilage, the epiphyseal plate, separates
the epiphysis from the diaphysis.
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BONE GROWTH
Impo
¡ Subsequent growth in diameter results from continued
formation of compact bone by osteoblasts from the
periosteum.
¡ Subsequent growth in length occurs as bone replaces
cartilage on the diaphysis side of each epiphyseal plate.
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BONE GROWTH
¡ The opposing actions of osteoblasts and osteoclasts
continually reshape the bone as it grows.
¡ Growth usually continues until about age 25 when
epiphyseal plates are completely replaced by bone
tissue.
¡ After this, growth in the length of a bone is not
possible.
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HOMEOSTASIS OF BONE
¡ Bones are dynamic, living organs, and they are continually
restructured throughout life.
¡ This occurs by the removal of calcium salts by osteoclasts and by
the deposition of new bone matrix by osteoblasts.
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HOMEOSTASIS OF BONE
Physical activity causes the density and
the volume of bones to be maintained
or increased, though inactivity results
in a reduction in bone density and
volume. HOW???
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¡ When you exercise regularly, your osteoblasts adapt to more
building, meaning more calcium deposition. Thus, the bone getting
denser.
¡ So what happens in practice is that places exposed to more load put
on more bone, while those exposed to less load put on less bone.
¡ This process takes place in the hypothalamus, a small yet complex
region of the brain.
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¡ It happens through a peptide hormone, Growth hormone, that is
secreted from the pituitary gland under the control of the
hypothalamus.
¡ There is a direct proportion between physical activity and GH
release.
¡ Growth hormone stimulates bone turnover as it increases
osteoblast number and function.
¡ It also stimulates bone resorption through unknown mechanisms.
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So, when do we exactly stop
this growth mechanism?
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¡ Truth is we never stop secreting growth hormone. However,
¡ Growth hormone GH and IGF-1 levels peak during puberty then
gradually decline after the age of 30
¡ Exercise can really stimulate the production of GH and it in turn can
be used in prevention and treatment of osteoporosis.
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BONE HOMEOSTASIS
¡ Calcium salts might be removed from bones to meet
body needs when dietary calcium salts return to a
sufficient level, they are used to form new bone matrix.
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SUMMARY
¡ Intramembranous bones are first formed by connective tissue membranes, which are replaced by bone tissue.
¡ Connective tissue cells are transformed into osteoblasts, which deposit the spongy bone within the membrane.
¡ Osteoblasts from the periosteum form a layer of compact bone over the spongy layer.
¡ Endochondral bones are first formed of hyaline cartilage, which is later replaced by bone tissue.
¡ In long bones, a primary ossification center forms in the center of the diaphysis and extends towards the
epiphysis.
¡ Secondary ossification centers form in the epiphysis.
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SUMMARY
¡ Osteoclasts hollow out the medullary cavity and reshape the bone.
¡ The concentration of protein fibers decreases with age.
¡ The bones of older persons tend to be brittle and weak due to the loss of fibers and calcium salts, respectively.
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