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CHAPTER 3: SKELETAL SYSTEM
Learning Outcomes
This section provides detailed information about types of bones, joint and
joint movements, functions of the skeletal system and bone formation.
1. Illustrate the bone and embryonic formations
2. Show the correct movements of the body
3. Analyze the structural and functional classification and types of joints.
Introduction to the Skeletal System
Despite what seems to be a solid, dry, inert material, bone is in fact a
complex living organism that is being recreated constantly; bone is metabolically
active. As old bone dies new bone is being rebuilt. There are a number of complex
activities occurring as bone is destroyed and reformed. Bones are therefore living
organs that are made up of a number of different tissues, and this includes bone
tissue.
The human skeleton, in contrast to other skeletons, is built to move erect
as opposed to walking on all fours. The skeleton provides us with shape and the
power to move, but it cannot do this in isolation. It needs many other systems of
the body for it to function properly – for example, the nervous system and the
muscles and for the body to move in its various and complex ways (the spine, for
example, allows us to twist and bend); this is attributed to the joints and their
ability to articulate.
Functions:
1. Support
• The bones of the legs, pelvic girdle, and vertebral column
support the weight of the erect body.
• The mandible (jawbone) supports the teeth.
• Other bones support various organs and tissues.
2. Protection
• The bones of the skull protect the brain.
• Ribs and sternum (breastbone) protect the lungs and heart.
• Vertebrae protect the spinal cord.
3. Movement
• Skeletal muscles use the bones as levers to move the body.
4. Reservoir for minerals and adipose tissue
• 99% of the body’s calcium is stored in bone.
• 85% of the body’s phosphorous is stored in bone.
• Adipose tissue is found in the marrow of certain bones.
5. Hematopoiesis
• A.k.a. blood cell formation.
• All blood cells are made in the marrow of certain bones.
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Fig. 4.1 Intramembranous ossification. Tortora and Direckson 2009
Bone Length and thickness
As the person grows (e.g. during infancy, childhood and adolescence), long
bones grow in length and thickness. This longitudinal growth and expansion of
thickness continues until the person is usually 15 years of age in girls and 16
years of age in boys. The chondrocytes present in the epiphyseal plate are
constantly dividing, and this activity is related to the length of bone growth. As
adolescence ends, the formation of new cells decreases, and between the ages of
18 and 25 years this activity ceases altogether. Growth of bone (thickness) occurs
as the cells in the perichondrium differentiate into osteoblasts; the osteoblasts
then develop into osteocytes. Lamella are added to the bone surface, and osteons
(the basic units of structure of the adult compact bone) are formed. Osteoblastic
and osteoclastic activity occurs, and the result is an enlarged medullary cavity
and thicker bone is formed.
Bone Structure and Blood
Supply
Blood supply to the bone comes
via three routes:
• the Haversian canals
• the Volkmann canals
• the vessels.
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Fig.4. 2 Endochondral ossification of the tibia. Tortora and Derrickson (2009)
Fig.4. 3 Bone Structure and terminologies
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Fig. 4.4 Organization of bones based on shape.
FRACTURES
•
Despite its mineral strength, bone may crack or even break if subjected to
extreme loads, sudden impacts, or stresses from unusual directions.
–
•
The damage produced constitutes a fracture.
The proper healing of a fracture depends on whether or not, the blood
supply and cellular components of the periosteum and endosteum survive.
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Fig. 4.5 Steps in Fracture Repair Pearson 2018
Fig. 4.6 Types of Fracture. Pearson 2017
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Divisions of the Skeleton
The adult human skeleton usually consists of 206 named bones. These
bones can be grouped in two divisions: axial skeleton and appendicular skeleton.
The 80 bones of the axial skeleton form the vertical axis of the body. They include
the bones of the head, vertebral column, ribs and breastbone or sternum. The
appendicular skeleton consists of 126 bones and includes the free appendages
and their attachments to the axial skeleton. The free appendages are the upper
and lower extremities, or limbs, and their attachments which are called girdles.
The named bones of the body are listed below by category.
Fig.4. 7 The Skeletal System Structure. Pearson 2018
The Axial Skeleton
•
•
Forms the longitudinal part of the body
Divided into three parts
• Skull
• Vertebral column
• Bony thorax
The Skull
• Two sets of bones
•
•
Cranium
Facial bones
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•
Bones are joined by sutures
•
Only the mandible is attached by a freely movable joint
Fig. 4.8
The Skull
Bones of the Skull
Paranasal Sinuses
•
•
Hollow portions of bones surrounding the nasal cavity
Functions of paranasal sinuses
o Lighten the skull
o Give resonance and amplification to voice
Fig. 4.9
Fig. 4.10
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Fig. 4.11
Fig. 4.12
The Auditory Ossicles
Vertebral Column
Fig. 4.17. Pearson 2009
The Vertebral Column
• Vertebrae
separated by
intervertebral
discs
• The spine has a
normal curvature
• Each vertebrae is
given a name
according to its
location
Fig. 4.18 Pearson 2009
Structure of a Typical Vertebrae
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Fig. 4. 19
The Bony Thorax
• Forms a
cage to
protect
major
organs
• Made-up of
three parts
• Sternum
• Ribs
• Thoracic
vertebrae
The Appendicular Skeleton
•
Limbs (appendages)
•
Pectoral girdle
•
Pelvic girdle
The Pectoral (Shoulder) Girdle
•
•
Composed of two bones
•
Clavicle – collarbone
•
Scapula – shoulder blade
These bones allow the upper limb to have exceptionally free movement
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Fig. 4.20
Bones of the Shoulder Girdle
Fig. 4.21
Bones of the Upper Limb
• The arm is
formed by a
single bone
• Humer
us
Fig. 4.22
• The forearm
has two
bones
• Ulna
• Radius
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Fig. 4. 23
Bones of the Upper Limb
• The hand
• Carpals –
wrist
• Metacarpal
s – palm
• Phalanges
– fingers
Fig. 4.24
The Pelvis
Fig. 4.25
Gender Differences of the Pelvis
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Fig. 4.26
Fig. 4.27
Bones of the Lower Limbs
• The leg has
two bones
• Tibia
• Fibula
Fig. 4.28
• The foot
• Tarsus
– ankle
• Metatar
sals –
sole
• Phalan
ges –
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Joints
A joint is the point at which two or more bones meet. Joints are sometimes also
called articulations. There are a number of ways of classifying joints; for
example:
Fig. 4.29
Fig. 30
2. Fibrous joints:
•
Bones held together by
collagenous fibers
extending from the
matrix of one bone into
the matrix of the next.
o No joint cavity
o Skull sutures,
teeth in joints,
distal radioulnar
joints & tibiofibular
joints
3. Cartilaginous joints:
•
•
Fig. 4.31
Bones held together by cartilage; no joint cavity
Epiphyseal plates of long bones, costosternal joints, pubic
symphysis, intervertebral discs
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4.32 Types of joints, Tortora 2016
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Articulations
(Movements)
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Summary Review : The Skeletal System
Here is what we have learned from Introduction to the Skeletal System:
•
•
•
•
•
•
•
•
The human skeleton is well-adapted for the functions it must perform.
Functions of bones include support, protection, movement, mineral
storage, and formation of blood cells.
There are two types of bone tissue: compact and spongy. Compact bone
consists of closely packed osteons, or haversian system. Spongy bone
consists of plates of bone, called trabeculae, around irregular spaces that
contain red bone marrow.
Osteogenesis is the process of bone formation. Three types of cells,
osteoblasts, osteocytes, and osteoclasts, are involved in bone formation
and remodeling.
In intramembranous ossification, connective tissue membranes are
replaced by bone. This process occurs in the flat bones of the skull. In
endochondral ossification, bone tissue replaces hyaline cartilage models.
Most bones are formed in this manner.
Bones grow in length at the epiphyseal plate between the diaphysis and
the epiphysis. When the epiphyseal plate completely ossifies, bones no
longer increase in length.
Bones may be classified as long, short, flat, or irregular. The diaphysis of
a long bone is the central shaft. There is an epiphysis at each end of the
diaphysis.
The adult human skeleton usually consists of 206 named bones and
these bones can be grouped in two divisions: axial skeleton and
appendicular skeleton.
The bones of the skeleton are grouped in two divisions: axial skeleton
and appendicular skeleton.