The Skeletal
System
Chapter 5
The Skeletal System
 Parts of the skeletal system
 Bones
 Joints
 Cartilage
 Ligaments
 Divided into two divisions
 Axial Skeleton – torso and head
 Appendicular Skeleton - limbs
Functions of the Bones
 Support of the body
 Protection of the soft organs
 Movement due to attached skeletal muscles
 Storage of Minerals and fats
 Blood cell formation
Bones of the Human Body
 The skeleton has 206 bones
 Two basic types of bone tissue
 Compact bone
 Homogeneous
 Very dense and strong
 Spongy bone
 Small needle-like
pieces of bone
 Many open spaces
 Purpose?
Figure 5.2b
Classification of Bones
• Long Bones
• Description? Examples?
• Short Bones
• Description? Examples?
• Flat bones
• Description? Examples?
• Irregular Bones
• Irregular shapes
• Do not fit into any other bone classification
category
• Examples?
Classification of Bones on the Basis
of Shape
Figure 5.1
Gross Anatomy of a Long Bone
 Diaphysis
 Shaft of the bone
 Composed primarily
of _________ bone
 Epiphysis
 Ends of the bone
 Composed primarily
of _________ bone
Figure 5.2a
Structures of a Long Bone
 Periosteum
 Outside covering of
the diaphysis
 “Skin of the bone”
 Vascular
 Meaning?
 Multiple functions
 Sharpey’s fibers
 Secure periosteum to
underlying bone
Figure 5.2c
Structures of a Long Bone
 Articular cartilage
 Covers external
surfaces of
epiphysis
 Hyaline cartilage
 Function?
Figure 5.2a
Structures of a Long Bone
 Medullary cavity
 Cavity of the shaft
 Contains yellow
marrow (mostly fat)
in adults
 Contains red marrow
(for blood cell
formation) in infants
Figure 5.2a
Structures of Long Bone
 Process – Projection from the bone
 Purposes
 Site of attachments for muscles
 Create joints
 Pathway for nerves, blood vessels
Microscopic Anatomy of Bone
 Osteon (Haversian System)
 Bone is built around a “canal”
 Tube-like openings in the bone
 DQ - What would these canals be used for?
 Two types of Canals
 Central (Haversian) canal
 Run longitudinally in the bode
 Perforating (Volkman’s) canal
 Perpendicular to the Haversian Canal
Microscopic Anatomy of Bone
Figure 5.3
Microscopic Anatomy of Bone
 Lacunae
 Tiny cavities
containing osteocytes
(bone cells)
 Lamellae
 Rings around the
central canal
 Sites of lacunae
Figure 5.3
Microscopic Anatomy of Bone
 Canaliculi
 Tiny canals
 Radiate from the
central canal to
lacunae
 Not the same as
Volkmann’s canal
 Purpose = diffusion
Figure 5.3
Bone Cells
 3 Types of Bone cells
 Osteocytes - Mature bone cell
 Osteoblast – Bone forming cell
 Osteoclast – Bone Destroying cell
 Break down bone matrix for remodeling and
release of calcium
Skeletal Functions
• Support and Protection:
• Bones create the shape of our body
• Examples?
• Bones provide a hard protective barrier
around vital organs
• Examples?
• Movement:
• Muscles attach to the bones across
joints
• Work like levers
Skeletal Functions
• Blood cell production:
• Hematopoiesis – the process of forming
blood cells
• Not always in the bone marrow
• As embryo develops, production is in the liver
and spleen
• Then switches to the marrow
• 2 types of Marrow
• Red
• Yellow
Hematopoiesis
• Red marrow produces erythrocytes,
leukocytes, and thrombocytes
• Which is RBC? WBC? Platelets?
• Red color is due to hemoglobin
• Infants have mostly red marrow
• Why would this be?
• As aging occurs, most red marrow is
replaced with yellow marrow
• Yellow stores fat
Storage of Minerals
• Minerals account for about 70% of
bone matrix
• Calcium #1
• When blood calcium levels are low
hormones stimulate osteoclasts to
break down bone tissue
• Why would they do this?
• High blood calcuim levels stimulate
osteoblasts to form bone
Changes in the Human Skeleton
 In a fetus, the skeleton is primarily hyaline
cartilage
 What happens to the cartilage as we
develop?
 Replaced by bone
 Cartilage remains in isolated areas
 Where?
Bone Growth and Development
(Endochondral)
 Replacement of cartilage begins in the
primary ossification center
 Occurs in the diaphysis
 What type of cell is active?
 Continues in secondary ossification sites
in epiphysis
 Epiphyseal plate is created between primary
and secondary ossification sites.
 You might know this by a different name
Bone Growth and Development
(Endochondral)
• During this process the Medullary Cavity
must be formed.
• How is this done?
• Growth Hormone (GH) and sex hormones
control bone growth
• DQ - When does bone growth stop?
• When the primary and secondary
ossification sites grow together, closing
the epiphyseal plate.
Long Bone Formation and Growth
Figure 5.4a
Long Bone Formation and Growth
Figure 5.4b
Bone Homeostasis
• To stay healthy, bone is continually resorbed
and deposited
 DQ - Why would this be?
 So old bone is broken down and new bone can
be formed.
 Controlled by two factors
 Calcium levels in blood
 Stress on bones
 Example: Running
 If this process becomes unbalanced bones
lose their mass and become weaker
Classification of Fractures
• Simple (aka closed)
• Break does not penetrate the skin
• Compound (aka open)
• The Broken bone
penetrates through
the skin
Types of fractures
• Greenstick –
• incomplete, only one side of bone
• Transverse –
• Complete break to right angle to lengthwise of
long bone. Usually traumatic
• Oblique • Rare. Break at an angle
• Comminuted –
• More than two fragments broken off. traumatic
Types of fractures
Types of fractures
• Impacted –
• Occurs after a fall, vertebral column
compressed, and cracks
• Pathologic • Disorder that weakens the bone, leading to a
fracture
• Stress • A bone becomes stressed from over use.
• Can cause slight breaks
Repair Bone fractures
• Break causes blood vessels to rupture
• What does this cause?
• Osteoclasts will remove bone
fragments
• New vessels and Fibrocartilage form
around break
• Cartilage will be replaced by a
bony callus
• Cell types - osteoblasts
Repair of fracture
(Bone remodeling)
• There is typically more bone
produced at site of healing
• Why would this be?
• How does the bone get back to
normal?
• Osteoclasts will reshape to like
original bone
Skeletal Differences
• Adult vs. Infant skull
• Infant - face is small in comparison to
cranial bones
• How much of an adults length is made of
the head? Infants?
• Adults = about 1/8
Infants = about 1/4
• Fontanels - soft spots
• What is the purpose of fontanels?
• Provides room for the brain to grow
Skeletal Disorders
• Use your book to come up with a one
sentences summary of each of the
following disorders.
Osteoarthritis
Rheumatoid arthritis
Gouty arthritis (Gout)
Osteoporosis
Scoliosis
Kyphosis
Lordosis
Osteomyelitis – bacterial infection of the
bone, causing pain and discomfort.
• Paget disease – Bone remodeling is not
balanced leading to abnormal and
enlarged but brittle bones.
•
•
•
•
•
•
•
•
Skeletal Disorders
 Due to poor posture, Helga has felt like she is
constantly leaning forward. An X-ray reveals
excessive flexion in the thoracic curvature.
 Kyphosis
 Jimbo was a four sport athlete in high school
and has continued with high impact
excercises. He has complained of stiffness in
his knees. He has also started to develop bone
spurs, which hinder movement.
 Osteoarthritis
Skeletal Disorders
 Phoebe’s phalanges have fused together, so
she is unable to flex his fingers. Her family has
a history of this disorder and it is discovered
that she has a high quantity of uric acid in her
blood.
 Gouty Arthritis
 Whitney’s muscles in her lumbar region are
excessively tight. This has caused the lumbar
vertebrae to curve laterally towards the
tightened muscles.
 Scoliosis
Skeletal disorders
 Gertrude has experienced a dull pain in her
lower back. An x-ray revealed a fracture of
her L2, yet Gertrude does not recall any
impact that may have caused the break.
 Osteoporosis
 Will-i-am experienced a compound fracture a
week ago and the bones were reduced while
on a hunting trip. He has since developed a
fever and severe pain in the area of injury. It is
suspected that he has a bacterial infection.

Osteomyelitis
Skeletal Disorders
 Mac has experienced pain in his bones.
Through an x-ray it has been determined that
his femur is misshapen. He has also been told
by his doctor that he has a high alkaline
phosphatase level in his blood.
 Paget’s Disease
 Marge’s joints have become swollen,
reddened and tender. It has been very painful
to move. This seems to to go away, but it
keeps coming back.
 Rheumatoid Arthritis
Joints
• Every bone in the body articulates with
another bone
• Except the hyoid
• Not all joints are movable.
• Where would immovable joints be found?
• 3 Types of Joints
• Fibrous
• Cartilaginous
• Synovial
Types of Joints
• Fibrous
• Immovable
• Examples?
• Cartilaginous
• Both ends connected by cartilage
• Immovable to limited movement
• Examples?
• Synovial
• surrounded by joint cavity
• Contain hyaline cartilage, ligaments, and
synovial fluid
• Examples?
Knee injuries
 Torn ACL, MCL,
PCL, LCL
Types of synovial joints
• Plane - no rotation – bones glide past one another
• Example
• Hinge - move on one axis – like a door hinge
• Example
• Pivot - rotation around an axis
• Example
• Condyloid - move on two axes
• Example
• Saddle – move on two axes
• Example
• Ball and socket - move in all axes
• Example
Types of Synovial Joints Based
on Shape
Types of Synovial Joints Based
on Shape
Figure 5.29d–f
Motions
• Flexion-Angle
• Dorsiflexion – raising
decreases
foot to the shin
• Extension -
• Plantar flexion -
• Rotation – Move
• Elevation – raise a
• Abduction -
• Depression – lower a
around an axis
• Adduction • Circumduction -
body part
body part
• Supination • Pronation -