SKELETAL SYSTEM
TYPES OF BONES
LONG: humerus
 SHORT: carpals
 FLAT: frontal bone
 IRREGULAR: vertebrae

Categorizing bones
developmentally…

Endochondral
– develop from pieces of cartilage deposited
as sheets of tissue in embryo
– Face, appendages

Dermal
– Formed from sheets of fibrous connective
tissue
– Clavicle, scapula, flat cranial bones

Alveolar
– Teeth
– Specialized groupings of bone cells

Sesamoid
– Form within tendons due to stress on
tendon
– Patella, pisiform, various metacarpal,
metatarsal bones

Wormian
– Small, irregular, isolated; develop within
sutures
BONE STRUCTURE
Periosteum
 “To
surround
the bone”
 Fibrous membrane, covers surface of
the bone EXCEPT at the joint surfaces.
 Contains nerves and blood vessels
Nutrition, sensation
 This
is where the tendons & ligaments
attach to the bone.
Red marrow
spaces
(surrounded
by
trabeculae)
Yellow Marrow
Epiphysis
At the end of each bone
Made of cancellous or spongy bone
Network of bone called trabeculae
Spaces contain red marrow
Site of hematopoiesis (blood cell production)
Outer surface is compact bone
Within joints, surfaces covered with
hyaline articular cartilage
Epiphysial Plate

Also called the “growth plate”;
– indicates that additional bone growth is possible
Site of bone elongation
 Ossifies over time

– then callled epiphysial line
Epiphyseal
Plate
Diaphysis
“to grow apart”
Hollow Tube
Made of compact bone:
organized into osteons
Rigid but light
Medullary Cavity
Hollow area inside diaphysis
Bordered by spongy bone
Lined by a thin membrane called the
endosteum
Capable of generating new bone cells
Adults: contains soft, yellow bone marrow
Mostly adipose tissue
Food reserve for bone cells
 Children: more red marrow
Two kinds
of bone
Cancellous/Trabecular
(Spongy)
80% of bone
many spaces filled with
marrow
Compact (cortical)
 20% of skeleton structure
 80% of skeletal weight
 Structural unit = osteon
The Osteon
The structural unit of bone
The OSTEON: Found in compact bone
 Matrix is organized into numerous structural
units called osteons or Haversian systems.
 Consists of calcified matrix arranged in
concentric rings called concentric lamellae
The Osteon
 The
rings surround an opening called the
Central (Haversian) Canal

Canal contains blood, lymph vessels and
nerves
The Osteon

Mature bone cells = osteocytes
– Secrete bone matrix

Composed of collagen fibers and protein (osteocalcin)
The cell resides in a space called a lacuna
 Canals, called canaliculi, connect the
osteocytes to one another

More on the Osteon
Nutrients pass
from the blood vessel in the central canal
through the canaliculi
to the osteocytes
What can you identify?
The Osteon
 Central
canals are connected by a
horizontal blood vessel housed within
the Volkmann’s Canals
JOINTS
Classification:

Structural
– Tissue composition, structural complexity
– Cartilaginous, fibrous, synovial

Functional
– Type of movement allowed
– Synarthrotic, amphiarthrotic, diarthrotic
Bursa – Accessory
Structure


Sac-like space made of fibrous tissue
Synovial fluid
– thick, lubricating fluid
– Nourishes, protects joints and surface
– Secreted by epithelial cells


Found in articular areas where rubbing between
skin, muscle, ligaments, or bones could occur
Can become inflamed/damaged = bursitis
Synarthrotic Joint
(Immovable Joints)
Fibrous Joint
Produce NO movement
 Bone connected to bone by fibrous tissue
 Purpose: to securely hold two bones
together
 Include

– Sutures of the skull (synostoses/sutures)
– Skull to teeth (gomphosis)
– Tibia and fibula (syndemosis)
Amphiarthrotic Joint
(Semi-movable)
Cartilaginous
 Bone connects to bone via cartilage
 Allows slight movement
 Includes
– Pubic symphisis
– Vertebrae
Diarthrotic/Synovial Joint


Allows much movement; joint cavity lined by synovial
membranes
Some types
– Ball & Socket: Shoulder, Hip
– Hinge: Knee, Shoulder
– Pivot: Atlas/Axis
– Gliding: Between carpal bones, between
tarsal bones
– Saddle: thumb
– Ellipsoid/Condyloid: wrist
BONE DEVELOPMENT AND
HEALING
Osteowhat?
The first crystals of bone that
form are pointed and needle-like:
called spicules.
 Osteoblasts
secrete a mineralized
matrix
 Once the osteoblast is surrounded by its
matrix, it’s called an osteocyte, a bone
cell.
 Osteoclasts break down bone.
Ossification
Conversion of embryonic tissues into
recognizable bone
 2 ways:

– Endochondral

Long bones
– Intramembranous

Flat bones
– Combination – irregular bones
Ossification
Ossification

Mesodermal cells form cartilage centers
– Cartilage pegs form
– Restructured, filled with hydroxylapatite
(calcification)
Pegs formed by fibroblasts
 Osteoblasts and osteoclasts sculpt
growing bones

An osteoclast in action. Here an osteoclasts is eroding bone. The capsule
formed by such action is called a Howship's capsule (H). Similar to the
cell of the gut, osteoclasts have a ruffled border which increases the
surface area for bone resorption.
Direction of
Long Bone
Growth

Epiphyseal plate made
of hyaline cartilage is
responsible for long
bone growth.

The direction of
growth is toward the
diaphysis

The newly forming
spongy bone (below
the growth plate) is
not clearly organized
as the older spongy
bone in the epiphysis
above the growth
plate.

Fontanelles – soft spots
– Regions of flat bone not fully ossified
– Completed during teenage years
HEALING
Fractures
Bone is cracked/splintered due to
physical injury
 Categorized by severity of break/angle
at which break occurs


Simple:
– Crack in bone structure
– May not be readily noticeable
– Some large; may involve bleeding, pain,
swelling
– Greenstick fractures

One side frayed from fracture; other twisted,
but not broken

Compound/comminuted
– Large fracture
– One (more) area is displaced, shattered
– Bleeding, swelling

Open
– Tearing of skin occurs; easily infected
Angle of break
Transverse (horizontal)
 Oblique (angle)
 Spiral (twisted)
 Angulation – bone changes overall
shape


For healing to occur, blood
accumulation must occur
Healing stages
1.
2.
3.
4.
5.
Fracture
Granulation
Callus
Lamellar bone
Normal contour