The skeletal system forms the mechanical framework
of the body (see for example bones
of the head and neck and bones
of the hands and feet).
The bones themselves are formed from
several different connective tissues, including:
- Bone (called "Osseous") tissue,
- Red Bone Marrow,
- Yellow Bone Marrow, and
This page is specifically about bone tissue (first item on the
Bone tissue is classified as either "compact bone",
or "spongy bone" depending on how the bone matrix and cells are
There are two main types of bone tissue, compact bone and spongy
bone. Individual bones in the body can be formed from
both of these types of bone tissue. The diagram on
the right shows the physical structure of a typical
(If need be read about different
types of bone - then come back to this page to
2.1 The structure of Compact Bone
Compact bone forms the outer layer of all bones and most
of the structure of "long bones" - see diagram (right).
It contains few spaces and provides protection and
to the bone/s around which it is the outer-layer, as well as
helping to enable the long bones to bear the stress
placed on them
by the weight of the body and the use to which the limbs are
put, e.g. due any heavy physical work.
The basic unit of Compact Bone
is an "osteon", which is
also known as a "Haversian System".
Each Haversian System (unit) has a cylindrical structure that
consists of four parts:
- A central tube called a Haversian
Canal, which contains blood
vessels and nerves.
The Haversian Canal is surrounded
by alternate layers of:
- Lamellae (the
word lamellae literally means "little
plates") are concentric rings of a strong
matrix formed from mineral salts including calcium
and phosphates and collagen fibres. The mineral
salts result in the hardness
of the bone structure, while the collagen fibres
contribute its strength.
- Lacunae are
the small spaces between the lamellae in
which contain the bone cells (called
- The lacunae are linked together
by minute channels called canaliculi.
canaliculi provide routes by which nutrients can reach the
osteocytes and waste products can leave them.
2.2 The Structure of Spongy Bone
Spongy Bone does
not include osteons (the basic unit/s of
Compact Bone - see above).
bone consists of an irregular lattice of thin columns of
bone called trabeculae
(literally "little beams"), which contain lamellae, osteocytes, lacunae and canaliculi.
The spaces between the trabeculae of some spongy bones are
filled with red bone marrow.
Blood vessels from the periosteum (see diagram above-right),
penetrate into the trabeculae lattice allowing the osteocytes
in the trabeculae to receive nourishment from the blood passing
through the marrow cavities.