The Skeleton System
Chapter 8/ Part I
Joe Pistack MS/ED
The Skeletal System
The Skeletal System
Consists of:
 Bones
 Joints
 Cartilage
 Ligaments

The skeletal system consists of 206 bones.
The Skeletal System
Functions:
 Bones of the lower extremities support the
weight of the body.
 Support and protect the soft body organs.
 Enables the body to move about.
 Store a number of minerals, calcium and
phosphorus are most important.
 Red bone marrow produces blood cells.

Classification of Bones
Bones are classified as follows:
 Long bones-longer than they are wide. Found in the arms
and legs.
Classification of Bones

Short Bones-shaped like cubes and are found primarily in
the wrists and ankles.
Classification of Bones

Flat Bones-thin, flat, curved. Form the ribs, breastbone and
skull.
Classification of Bones

Irregular Bones-differently shaped, not classified as long ,
short, or flat. Include hip bones, vertebrae, and various
bones in the skull.
Tissue and Bone Formation

Osseous tissue-another word for bone.

Osteocytes-bone cells.
- secrete an intercellular matrix.
-contain calcium, minerals and protein
fibers.
Two Types of Bone



Compact BoneDense hard bone.
Found in shafts of long
bones and outer surfaces
of other bones.
Two Types of Bone




Spongy BoneAlso called cancellous
bone.
Less dense
Found at the ends of long
bones and in the center of
other bones.
Compact Bone

Microscopically-compact bone and spongy bone look
different.

Compact bone is tightly packed, density gives it strength.

Osteon or haversion system-microscopic unit of compact
bone.

Each haversion system consists of mature osteocytes
arranged in concentric circles around large blood vessels.
Compact Bone

Area surrounding the osteocytes is filled with protein fibers,
calcium and other minerals.

Protein fibers provide elasticity.

Minerals make bone tissue hard and strong.

Compact bone consists of many haversian systems running
parallel to each other, system looks like a long cylinder.

Blood vessels run laterally to the haversian system, this
ensures adequate blood supply to the bone tissue.
Compact Bone
Spongy Bone

Also called cancellous bone.

Does not have a haversian canal.

Bone tissue is arranged in plates called trabeculae.

Bony plates are separated by holes that give it a punchedout “swiss cheese” appearance.

Holes are important for: (1)decrease the weight of bone,
make it lighter, and (2)contain red bone marrow.
Spongy Bone

Red bone marrow richly supplies the spongy bone with
blood cells for use throughout the body.

Spongy bone is located in short, flat, and irregular bones.

Spongy bone is found in the ends of long bones.
Long Bone

Made up of an
arrangement of compact
and spongy tissue, which
accounts for its strength.

Contains sites of growth
and reshaping and
structures associated with
joints.
Long Bone
Parts of a long bone:
 Diaphysis-long shaft of the
bone, composed primarily of
compact bone, therefore it
provides strength.

Epiphysis-enlarged ends of
the long bone. Articulates
or meets with a second
bone at a joint. Consists of
a thin layer of compact bone
overlying spongy bone.
Epiphysis are covered with
cartilage.
Long Bone

Epiphyseal disc-band of
hyaline cartilage located at
each end, between the
epiphysis and the diaphysis in
a growing bone. This band
of cartilage is the epiphyseal
disc or growth plate.

Medullary cavity-hollow
center of the diaphysis. The
inside is lined with
connective tissue called the
endosteum.
Long bone

Periosteum-tough, fibrous
connective tissue membrane
that covers the outside of
the diaphysis.

Anchored firmly to the
outside of bone on all
surfaces except articular
cartilage.

Periosteum protects bone,
serves as a point of
attachment for muscle,
contains blood vessels that
nourish underlying bone.
Long Bone

Injury to the periosteum
may have serious
consequences to the
health of the bone since
this structure carries the
blood supply.

Articular Cartilage-found on
the outer surface of the
epiphysis, forms a smooth
shiny surface that
decreases friction within a
joint.
Ossification

Ossification-the formation of bone.

Occurs differently in flat and long bones.

In the fetus, flat bones in the skull consist of thin connective tissue
membrane.

Ossification begins when the osteoblasts (bone forming cells),
migrate to the region of the flat bones.

The osteoblasts secrete calcium and other minerals into the spaces
between the membranes, thereby forming bone.

This process involves the replacement of thin membrane with bone.
Ossification of Long Bones

Ossification of long bones occurs as bone tissue replaces
cartilage.

The fetal skeleton is composed largely of cartilage.

As the baby matures, osteoblasts invade the cartilage and
gradually replace it with bone until all but the articular
cartilage and the epiphyseal disc have been replaced by
bone.

Isolated pieces of cartilage, such as the bridge of the nose
and parts of the ribs remain.
Ossification
Growing Bones

Two types of bone growth occurs from infancy to adulthood.
(1)Longitudinally-determines the height of an individual.
(2)Thicker & wider-to support the weight of the adult.

Longitudinally-bone grows at the epiphyseal disc, (also called the growth
plate).

Cartilage adjacent to the epiphysis continues to multiply and grow toward
the diaphysis.

Cartilage next to the diaphysis is invaded by osteoblasts and become
ossified.

As long as the cartilage continues to form within the epiphyseal disc, the
bone will continue to lengthen.
Growing Bones

Longitudinal bone growth ceases when the epiphyseal
disc becomes ossified and fused.

Growth hormone stimulates growth at the epiphyseal
disc, making the child taller.

The sex hormones estrogen and testosterone cause the
epiphyseal disc to fuse, inhibiting further longitudinal
growth.

The epiphyseal disc is more sensitive to estrogen, this
causes girls to tend to be shorter than boys.
Growing Bones

Longitudinal growth generally ceases after puberty.

Injury to the epiphyseal disc may impair longitudinal bone
growth. Eg. Injured leg shorter than uninjured leg.

Giantism- hypersecretion of growth hormone.

Dwarfism- undersecretion of growth hormone.
Growth Hormone Abnormalities
Giantism
Dwarfism
Growing Thicker and Wider

After longitudinal bone growth ceases, bones continue to
increase in thickness and width.

Bones are continuously being reshaped.

Bone reshaping is accomplished by a combination of the
actions of osteoblasts and osteoclasts.

Osteoblasts- bone forming cells.

Osteoclasts- bone destroying cells.
Growing Bones

Osteoblastic Activity: While osteoblasts build new bone,
osteoclasts, found on the inner bone surface break down
bone tissue, thereby hollowing out the interior of the
bone.

Osteoclastic Activity is like sculpting, the bricklayer lays the
bricks and the sculptor will hollow out the middle so that
it is not too heavy.

Bone resorption-(not reabsorption)-process whereby
osteoclasts breakdown bone matrix.
Growing Bones

Bone resorption- widens the bone, moves calcium from the
bone to the blood.

Bone resorption plays a crucial role in blood calcium levels.

Weight-bearing – factor that stimulates bone growth.

Exercise and weight bearing keep calcium in the bone and
increase bone mass.

Bedridden and sedentary people tend to lose bone mass
causing bones to be easily broken when stressed.
Surface Markings

Surface of bones appears
bumpy and irregular.

Appearance is due to
numerous ridges,
projections, depressions, and
grooves called bone surface
markings.

These bone surface
markings serve as points of
attachment for muscles,
tendons and ligaments.
Condyle

Condyle- large rounded
knob that usually
articulates with another
bone.
Epicondyle

Epicondyle- an enlargement
near or above a condyle.
Bone Markings

Head- an enlarged and
rounded end of a bone.
Bone Markings

Facet- a small flattened
surface.
Bone Markings

Crest- a ridge on a bone
Bone Markings
Process-a prominent
projection on a bone.
Bone Markings
Spine- sharp projection.
Bone Markings
Tubercle (tuberosity)- a
knoblike projection.
Bone Markings
Trochantor- a large
(tuberosity) found only on
the femur.
Bone Markings
Depressions/Openings
Foramen- an opening through
a bone, usually serves as a
passageway for nerves,
blood vessels, and
ligaments.
Bone Markings
Fossa- a depression or
groove.
Bone Markings
Meatus-a tunnel or tubelike
passageway.
Bone Markings

Sinus-a cavity or hollow
space.
Fractures
Fractures- break in the bone.

Simple Fracture- a break in which the overlying skin
remains intact. Local tissue damage is minimal.

Compound Fracture- a broken bone that also pierced the
skin. Ends of the broken bone usually cause extensive
tissue damage.

Incomplete Fracture- (greenstick)-usually occurs in children,
the break is incomplete because the child’s bone is still
made up of some cartilaginous material.
Common Types of Fractures