Introduction
 A skeleton is the bones of
a human or animal body
that form the framework
of the body, support the
muscles and organs, and
protect the inner organs.
 About 206 bones
 At birth, there are over
270 bones in an infant
human's body
 2 Main Divisions
– Axial &
Appendicular
 Bones do not
make up most of
a body’s mass
 There are five
types of bones in
the human body:
long, short, flat,
irregular, and
sesamoid.
Long Bones
1. Epiphysis
2. Diaphysis
3. Articular Cartilage
4. Periosteum
 Long Bone Structure
 Characterized by a shaft, the diaphysis, that is much
longer than it is wide.
 A long bone’s surface is covered by a tough
membrane called the periosteum.
 Periosteum is a white, double layered membrane
that covers the entire surface of bone except for the
joint surfaces and is richly supplied with nerve fibers
and blood vessels.
 Under the periosteum is a hard material called
compact bone, and this part of the bone gives all
bones their strength and rigidity.
 Compact bone is composed of cylinders made of
mineral crystals and protein fibers called lamellae.
 Each lamellae is made up
of a narrow channel
called a Haversian canal,
which contains the blood
vessels in compact bone.
 Surrounding each
Haversian canal are
protein fibers and
osteocytes.
 Osteocytes are a specific
type of bone
cell.
 Beneath some compact
bone is a network of
connective tissue called
spongy bone.
 Spongy bone is less dense
bone tissue that has many
open spaces.
 Bone Marrow
 Bone marrow is a soft tissue inside some
bones that can be either red or yellow.
 The type of bone marrow present determines
both its composition and function.
 Medullary Cavity –
hollow chamber filled
with bone marrow
 Red Marrow (blood)
 Yellow Marrow (fat)
 Endosteum - lining of
the medullary
Other types of bones
 Short bones are cube-
shaped, and have only a
thin layer of compact
bone surrounding a
spongy interior.
Examples: wrist and
ankle, as are the
sesamoid bones.
 Flat bones are thin and generally curved, with
two parallel layers of compact bones
sandwiching a layer of spongy bone. Example:
Most of the bones of the skull, sternum.
 Sesamoid bones are bones embedded in
tendons. Since they act to hold the tendon
further away from the joint, the angle of the
tendon is increased and thus the leverage of
the muscle is increased. Examples: patella and
the pisiform.
 Irregular bones do not fit into other bone categories.
 Consist of thin layers of compact bone surrounding a
spongy interior.
 Irregular shape is due to their many centers of ossification
or because they contain bony sinuses. The bones of the
spine, pelvis, and some bones of the skull.
Bone Development
 During fetal development, all bones starts as cartilage
 Cartilage will slowly be replaced by actual bone. This
process is called ossification.
 Epiphyseal disk (growth plate) is a band of cartilage
between the epiphysis and diaphysis
 These areas increase bone length as the cells ossify
 Cartilage becomes osteoblasts, then become osteocytes
 The epiphyseal disk/plate is found at the joint
ends of long bones and is composed of
cartilage. This area of bone will eventually
become mature bone.
Joints
 The place where two bones
meet is known as a joint.
 Three major kinds of joints
are found in the human
body
1. Fixed – no movement
2. Semi-movable – limited
movement
3. Movable – wide range of
movement
Moveable joints
 Hinge, ball-and-socket, pivot, saddle, and gliding
Moveable joints
 Hinge joint - allows limited movement in only one
plane.
 Ball-and-socket joint - allows 360 degree movement
in 2 planes.
 Pivot joint - allows 180 degree movement in only one
plane.
 Saddle joint - allows 360 degree movement in only
one plane.
 Gliding joint - allows bones to slide over one another.
Joint Structure
 Helps movable joints deal with the pressure and
stress of everyday life.
 Covered with cartilage and secrete synovial fluid to
reduce friction.
 Joints are connected with ligaments to aid in joint
movement.
 Even with all this protection a joint can still be
injured.
Arthritis
 Rheumatoid
arthritis
develops when
the immune
system begins to
attack body
tissues, & joints
become stiff &
deformed.
 Osteoarthritis is a degenerative joint disease in
which the cartilage covering the surface of bone
becomes thinner and rougher.