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THE SKELETAL SYSTEM: OVERVIEW
I. INTRODUCTION
 The organs of the skeletal system include
the bones and the structures that connect
bones to other structures, including
ligaments, tendons, and cartilages.
 The adult skeleton is composed of 206
separate bones.
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Division of skeleton
– Axial skeleton
 Includes the bones of:
 skull, vertebral column, and rib cage.
 These bones are involved in protection, support,
and carrying other body parts.
– Appendicular skeleton
 Bones of upper & lower limbs and the girdles
(shoulder bones and hip bones) that attach them
to the axial skeleton.
 Involved in locomotion and manipulation of the
environment.
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AXIAL SKELETON
Appendicular
SKELETON
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AXIAL SKELETON


a)
b)
1) Skull: 28 irregular shaped bones from
the skull.
The skull consists of two major division:
Cranium is formed by eight bones.
Face is formed by fourteen bones.
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AXIAL SKELETON
2) VERTEBRAL
COLUMN

1.
2.
3.
4.
5.
Divided into 5 main
regions
Cervical spine (7)
Thoracic spine (12)
Lumbar spine (5)
Sacrum (5)
Coccyx (4)
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Cervical, Thoracic, Lumbar, Sacrum
and Coccyx
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AXIAL SKELETON





THORAX
12 pairs of ribs
Joined to thoracic
vertebrae
Top 10 ribs joined to
sternum
Remaining two have
“free” ends – ‘floating’
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APPENDICULAR SKELETON

Forms mainly the
extremities of the body
and their connections to
the axial skeleton
Consists of
- limbs (arms & legs)
- shoulder and pelvic
girdles

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Bone Classification

4 types of bones:
–
Long Bones



–
Femur 
Much longer than they are
wide.
All bones of the limbs
except for the patella
(kneecap), and the bones
of the wrist and ankle.
Consists of a shaft plus 2
expanded ends.
Short Bones


Roughly cube shaped.
Bones of the wrist and the
ankle.
Carpal Bones
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Bone Classification

Types of bones:
–
Flat Bones


–
Thin, flattened, and usually
a bit curved.
Scapulae, sternum,
(shoulder blades), ribs and
most bones of the skull.
Sternum
Irregular Bones


Have weird shapes that fit
none of the 3 previous
classes.
Vertebrae, hip bones, 2
skull bones ( sphenoid
and the ethmoid bones).
Sphenoid
Bone
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Parts of long bone
1) diaphysis: main shaft like structure, its
hollow cylindrical shape, its functions of
providing strong support bone.
2) epiphysis: both end of long bone,
epiphysis have a bulbous shape that
provide generous space near joint.
 For muscle attachment and give stability
of joint.
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Parts of long bone
3) articular cartilage thin layer of hyaline
cartilage that covers joint surface.
4) Periosteum: dense white fibrous
membrane that cover bone except at joint
surface and anchoring bone to muscles.
5) Marrow cavity: a tubelike hollow space in
the diaphysis of long bone.
6) endosteum: a thin epithelial membrane
that line the medullry cavity.
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Long Bone
Structure
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Composition of bone matrix
Inorganic salts: the hardness of bone result
from the deposition of high specialized
chemical crystal of calcium and phosphorous
called hydroxyapatite, the process called
calcification in addition to mg, Na, sulphate
and fluoride.
2) Organic substance: collagenous fiber and
mixture protein and poly saccarids called
ground substance, provide support and
adhesion between cellular and fiberous.
 Chondroitin and glucosamine are required for
repair and maintenance of bone and cartilage.
1)
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Composition of bone matrix
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Types of bone cells
1. Osteoblasts
 Bone-forming cells found
in all bone surfaces
Bone-building cells.
 Synthesize and secrete
collagen fibers and other
organic components of
bone matrix.
 serve as a framework for
the deposition of calcium
and phosphate
calcification
The blue arrows indicate the
osteoblasts. The yellow arrows indicate
the bone matrix they’ve just secreted.17
Types of bone cells
2. Osteoclasts
 Giant multinucleate cells
 Responsible for the
active erosion of bone
minerals
 Contain large numbers
of mitochondria and
lysosomes
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Types of bone cells

3. Osteocytes—mature, nondividing
osteoblast surrounded by matrix, lying
within lacunae
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Bone Marrow
Specialized type of soft, diffuse connective
tissue; called myeloid tissue
 Site for the production of blood cells
 Found in medullary cavities of long bones
and in the spaces of spongy bone

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Microscopic Structure of Compact Bone
– Contains many cylindershaped structural units called
osteons, or Haversian systems
– Four types of structures make
up each osteon:
 Lamella—concentric,
cylinder-shaped layers of
calcified matrix

Lacunae—small spaces
containing tissue fluid in
which bone cells are located
between hard layers of the
lamella
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Microscopic Structure of
Compact Bone
Canaliculi—ultrasmall canals
radiating in all directions
from the lacunae and
connecting them to each
other and to the Haversian
canal
 Haversian canal—extends
lengthwise through the
center of each osteon and
contains blood vessels and
lymphatic vessels

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Microscopic Structure of
Compact Bone
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Bone Marrow

Two types of marrow are present during a
person’s lifetime:
– Red marrow
 Found in virtually all bones in an infant’s or child’s body
 Functions to produce red blood cells
– Yellow marrow
 As an individual ages, red marrow is replaced by yellow
marrow
 Marrow cells become saturated with fat and are no longer
active in blood cell production
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Bone Marrow
The main bones in an adult that still
contain red marrow include the ribs,
bodies of the vertebrae, the humerus, the
pelvis, and the femur
 Yellow marrow can alter to red marrow
during times of decreased blood supply,
such as with anemia, exposure to
radiation, and certain diseases

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Functions of Bone
Support—bones form the framework of the body and
contribute to the shape, alignment, and positioning of
the body parts
 Protection—bony “boxes” protect the delicate structures
they enclose
 Movement—bones with their joints constitute levers that
move as muscles contract
 Mineral storage—bones are the major reservoir for
calcium, phosphorus, and other minerals
 Hematopoiesis—blood cell formation is carried out by
myeloid tissue

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Regulation of Blood Calcium Levels

Skeletal system (cont.)
– Homeostasis of calcium ion concentration
essential for the following:
 Bone formation, remodeling, and repair
 Blood clotting
 Transmission of nerve impulses
 Maintenance of skeletal and cardiac muscle
contraction
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Regulation of Blood Calcium Levels

Mechanisms of calcium homeostasis
– Parathyroid hormone
 Primary regulator of calcium homeostasis
 Stimulates osteoclasts to initiate breakdown of
bone matrix and increase blood calcium levels
 Increases renal absorption of calcium from urine
 Stimulates vitamin D synthesis
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
Mechanisms of calcium homeostasis
(cont.)
– Calcitonin
 Protein hormone produced in the thyroid gland
 Produced in response to high blood calcium levels
 Stimulates bone deposition by osteoblasts
 Inhibits osteoclast activity
 Far less important in homeostasis of blood calcium
levels than parathyroid hormone
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Fracture Types
– Open (compound)  bone ends penetrate the
skin.
– Closed (simple)  bone ends don’t penetrate
the skin.
– Spiral  ragged break caused by excessive
twisting forces. Sports injury/Injury of abuse
– Greenstick bone breaks incompletely. One
side bent, one side broken. Common in
children whose bone contains more collagen
and are less mineralized
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Clinical
Conditions


Osteomalacia
– Literally “soft bones.”
– Includes many disorders in which osteoid
is produced but inadequately
mineralized.
 Causes can include insufficient
dietary calcium
 Insufficient vitamin D fortification or
insufficient exposure to sun light.
Rickets
– Children's form of osteomalacia
– More detrimental due to the fact that
their bones are still growing.
– Signs include bowed legs, and
deformities of the pelvis, ribs, and skull.
What about the above x-ray is
indicative of rickets?
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Clinical Conditions

Osteomyelitis
– Inflammation of bone
and bone marrow
caused by pus-forming
bacteria that enter the
body via a wound (e.g.,
compound fracture) or
migrate from a nearby
infection.
– Fatal before the advent
of antibiotics.
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Clinical
Conditions

Osteoporosis
– Osteoporosis is a
disease that thins and
weakens the bones to
the point that they
become fragile and
break easily. Women
and men with
osteoporosis most
often break bones in
the hip, spine, and
wrist, but any bone
can be affected. You
can't "catch"
osteoporosis or give it
to someone else.
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Any questions ???
The end
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