CHAPTER 7: SKELETAL SYSTEM
Bone Physiology and Joints
Human Skeleton
• Adult skeleton is composed of 206
bones (babies have 300).
• Two divisions:
– Axial Skeleton – bones that
form the longitudinal axis of
the body
– Appendicular skeleton – bones
of the limbs and girdles
• Skeletal system includes bones,
joints, cartilages, and ligaments
Functions of Bones
1. Support – internal
framework of body
2. Protection – protects
soft organs
3. Movement – muscles
attached by tendons
4. Storage – minerals and
fat
5. Blood cell formation –
marrow cavities
Classification of Bones
• Two basic types of bone tissue:
– Compact Bone: dense, looks smooth,
homogenous
– Spongy Bone: composed of small needlelike
pieces of bones and lots of open space
Types of Bones
• Long bone – ex. Include
humerus, femur
• Short bone – examples
include tarsals and
carpals
• Flat bone – include
frontal, ribs, and scapula
• Irregular bone – include
vertebrae, mandible, ear
bones
Long Bone Structure
• Diaphysis is hollow,
shaft like portion
composed of compact
bone
• The diaphysis is covered
and protected by a
fibrous connective
tissue membrane – the
periosteum.
Long Bone Structure
• Epiphyses are at ends
of long bone and made
up of a spongy or
cancellous bone
• Articular cartilage is
thin hyaline cartilage
that covers surface of
epiphyses to decrease
friction at joints
Long Bone Structure
• The cavity of the shaft is
storage for adipose
• Called yellow marrow or
medullary cavity.
• Red marrow is found in
infants in this area and
in flat bones of adults
(makes blood cells).
• Projections and
depressions mark bones
Bone Markings
Bone Markings
Microscopic Structure of Bone
• Mainly calcified matrix
of calcium salts with
collagenous fibers
• Matrix of compact bone
is made of thousands of
structures called
haversian systems
(osteons)
The Haversian System (Osteon)
• Lamellae – concentric,
cylinder-shaped rings of
calcified matrix
• Lacunae – microscopic spaces
containing bone cells osteocytes
• Canaliculi – tiny canals
radiating from lacunae,
connecting them with
haversian canal
• Haversian canal – extends
lengthwise through center of
each system; contains blood
and lymph vessels
Bone Formation - Ossification
• Skeleton pre-formed in
hyaline cartilage models
• Endochondral ossification
is a process that replaces
hyaline cartilage with true
bones
• Most change into bone but
not complete until age 25
• Osteoblasts within
membranous layers form
bone tissue
Resorption
• Resorption is the
process of breaking
down bone
• Osteoclasts – bone
destroying cells, release
Ca2+ into blood.
• When calcium levels are
too high, calcium is
deposited in bone
matrix as calcium salts
Joseph Merrick
• Lived 1862 – 1890 in
England
• Known as the “Elephant
Man” due to his deformities
• Thought to be either
Proteus Syndrome or
Neurofibromatosis
• Caused great enlargement
of bone and surrounding
tissue
• Died due to a dislocation of
the neck (strain from head
weight)
Merrick Skeleton
Bone Growth and Resorption
• Epiphyseal plate – site of
growth in length, by thickening
of hyaline cartilage followed by
ossification
• Disk located between diaphysis
and epiphysis
• Growth in diameter – medullary
cavity enlarged by osteoclasts
destroying bone added around
bone by osteoblasts
Bone Growth (con’t.)
• Opposing forces of bone
formation go on throughout
life
• Youth: Formation > resorption
• Young adult: balance
• Age 35-40+: Resorption
greater causing weaker bones
Bone Fractures and Repair
• Fracture is any break of a
bone
• Simple – skin remains
unbroken
• Compound – skin is broken
• Effective healing requires
alignment and
immobilization
• Reduction – proper set or
alignment of fracture
• Osteomyelitis – bone
infection
Steps in Bone Repair
1. Blood escapes from
ruptured blood vessels
– forms hematoma
2. Spongy bone and
fibrocartilage form in
damaged areas
3. A bony callus replaces
fibrocartilage
4. Osteoclasts remove
excess
Bone Diseases
• Osteoarthritis (OA) – chronic degenerative
condition that affects articular cartilage. Aging
– Cartilage softens and exposed bones thicken, restricting
movement
• Rheumatoid Arthritis (RA) – autoimmune disease
affecting synovial joints. Cause unknown.
– Thicken into pannus which erodes articular cartilage
• Osteoporosis – bone-thinning disease
– 50% of women, 20% of men
Vertebral Disorders
• Either congenital
or developmental
from disease, poor
posture or unequal
muscle pull on the
spine
Joints of the Skeletal System
• Articulations are joints
between two bones.
• They hold bones
together but also
permit movement
between them.
• Can be classified by
degree of movement or
by type of tissue
holding them together
Classification based on Movement
• Synarthrosis – nonmovable joints
• Amphiarthroses –
slightly movable joints
• Diarthoses – freely
movable joints
Classification based on Tissue
• Fibrous joints – united by fibrous tissue.
– Syndesmosis – long fibers of conn. Tissue
• Includes joints between distal ends of radius and ulna;
tibia and fibula
• Cartilaginous joints – united by cartilage.
– Example: pubic symphysis of pelvis
• Synovial joints – joints united by synovial
membrane
Synarthrotic Joints
Sutures – between flat bones
Gomphosis – roots of teeth to
maxilla and mandible
Amphiarthrotic Joints – slight
movement
Synchondrosis – growth plate
Symphysis – pad of cartilage
Diarthrotic – The Synovial Joint
• Articular cartilage
covers the ends of long
bones
• A joint capsule,
strengthened by
ligaments holds bones
together
• Synovial membrane
lines inside of joint
capsule
Menisci and Bursae
Menisci – divides some joints
into compartments
Bursae – between skin and
bony projections; cushion and
aid in movement of tendons
Types of Synovial Joints
• Ball-and-socket –
shoulder and hip
• Allow greatest variety of
movement
Condyloid
• Includes joint between
metacarpals and
phalanges
• Allow a wide variety of
movement
Gliding
• Articular surfaces are
nearly flat
• Movements are sliding
back and forth
• Include tarsals and
carpals
Hinge
• Include elbow and knee
• Permits movement in
only one plane
Pivot
• Found at proximal ends
of radius and ulna
• Permits rotational
movement
Saddle
• Found between
metacarpal and carpal
of thumb
• Allows variety of
movements
Types of Movements
•
•
•
•
•
•
Flexion – decrease angle
Extension – return from flexed position
Abduction – move away from midline
Adduction – move toward midline
Rotation – pivoting bone on central axis
Circumduction – moving distal end of bone in a
circle causing entire bone to circle
• Supination – turning palm out
• Pronation – turning palm in
More Movements
• Inversion – turning sole
inward
• Eversion – turning sole
outward
• Protraction – moving
body part forward
• Retraction – reverse of
protraction
• Elevation – moving part
upward
• Depression – moving part
downward