The Skeletal System
Anatomical defintions
Bone Classifications
Bones can vary in size and shape based
upon the function that they serve within
the body.
These are:
1. Long Bones
2. Short Bones
3. Sesamoid Bones
4. Flat Bones
5. Irregular Bones
Long Bones
Consist of a long shaft covered by
hard bone around a hollow centre
which contains yellow marrow
The two ends contain spongy bone
and red marrow
Long Bones
These bones are light but very
strong, and are the major weightbearing bones of the body
ie: The Femur in
the thigh
Short Bones
These bones are chunky, compact
bones that are strong and reinforced
by thickening of the bone tissue.
They contain spongy bone and allow
a variety of movements at joints
EG: Carpals in
the hand
Flat Bones
These bones are made up of two
strong layers of spongy bone.
They give protection to organs
beneath them and allow for large
areas of muscle attachment
EG: The Scapula
(Shoulder Blade)
Irregular Bones
These bones are made up of a thin
layer of compact bone containing a
mass of spongy bone
Irregular bones are reinforced where
extra strength is required
EG: Vertebrae
Sesamoid Bones
These are small bones that are
located within the tendons of some
joints. ie: the Patella
Developing Bones
A baby’s bones contain cartilage, a
tough, strong tissue is not as hard as
bone.
Cartilage is more flexible and tends to
bend a little without breaking
**Check the end of your nose**
Developing Bones
As the child grows this cartilage is
replaced by bone, becoming harder and
less flexible
Therefore it is easier for a teenager to
break a bone than it is for a child.
Note: If the bone is flexible it will bend under strain
before snapping!
Developing Bones
Bone cells are constantly replaced
throughout our lives.
During our growth spurt in puberty
our bones grow longer, stronger and
heavier
Developing Bones
Peak Bone Mass =
The formation of
mineral deposits
and compact bone
that helps give
maximum strength
to bone
Developing Bones
Osteoporosis =
A condition which
results in loss of
bone mass and
strength, making
bones more fragile
and likely to break
or fracture
SHORT BONE GROWTH
The outside of a short bone is formed by
cartilage. The cartilage grows until the final
shape of the bone is formed.
Meanwhile the bone ossifies (hardens into bone)
from the inside outwards. Eventually all cartilage
is ossified, and growth is complete.
LONG BONE GROWTH
Two growth processes responsible for bone
development.
First process:
OSTEOBLASTS (bone builders) – add bone to
the outside surface, enlarging and elongating the
bone.
OSTEOCLASTS (bone eaters) – tunnel out the
marrow cavity and internal spaces (these work at
the same time as osteoblasts.)
Long bone growth
Second process (greatest growth occurs):
EPIPHYSEAL PLATES (growth plates)
found at either end of the bone where the
shaft (diaphysis) meets the head or base
(epiphysis). These growth plates are made
of cartilage cells which multiply rapidly and
the outside cells ossify, increasing the length
of the shaft.
GROWTH HORMONE (GH)
GH - Responsible for most growth changes
occurring.
Produced by the pituitary gland, at the base of
the brain.
Growth Hormone:
(1) stimulates the epiphyseal plates to expand
and form bone
(2) increase protein uptake by the muscles,
therefore increasing muscle growth
FACTORS AFFECTING GROWTH
Basic control of growth is
genetic
Starvation and Malnutrition
can delay growth spurt
Major illness slow down
growth
Regular exercise has many
growth benefits
Aerobic exercise also
increases the size and
efficiency of the heart,
blood and lungs. However,
repetitive long distance
training for marathons or
triathlons may damage
epiphyseal plates.