Structure and Functions of Bone Tissue
Note: This page is part of the section
about the structure and function of different Tissue
Types, which is related to the section about Histology
and Cells (incl. structure
of animal cells, cell
division, mitosis, meiosis).
This "Tissue Types" section is included to complete description
of the knowledge of "Histology - The Cell" required by
some courses in First-Level Anatomy and Physiology. To read about
other tissue types see the list of on the left.
1.0 Where in the body is bone tissue
?
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,
- Periosteum,
- Red Bone Marrow,
- Yello Bone Marrow, and
- Endosteum.
This page is specifically about bone tissue (first item on the
above list).
Bone tissue is classified as either "compact bone",
or "spongy bone" depending on how the bone matrix and cells are
organized.
2.0 The Structure (Physical Description)
of bone tissue
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Above: Diagram
illustrating the Structure of Long Bones
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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 "long bone".
(If need be read about
different
types of bone - then come back to this page to continue.)
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
support
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 "osteocytes") are located.
- The lacunae are linked together by minute chanmnels called
canaliculi.
The
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).
Instead, spongy
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.
3.0 The Functions of bone tissue
The following table also appears on the page about The
Structure and Functions of Bones - due to overlap between differents sections
of course outlines.
 1.
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| Support |
The skeleton is the framework of the body,
it supports the softer tissues and provides
points of attachment for most skeletal muscles.
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2.
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Protection |
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The skeleton provides mechanical protection for many of
the body's internal organs, reducing risk of injury to
them.
For example, cranial bones protect the brain, vertebrae protect the spinal
cord, and the ribcage protects the heart and lungs.
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3.
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| Assisting in Movement |
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Skeletal muscles are attached to bones, therefore
when the associated muscles contract they cause bones
to move.
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4.
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| Storage of Minerals |
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Bone tissues store several minerals, including calcium
(Ca) and phosphorus (P). When required, bone releases
minerals into the blood - facilitating the balance
of minerals in the body.
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5.
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| Production of Blood Cells |
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This process takes place in the red bone marrow
inside some larger bones.
(Red Blood Cells, White Blood Cells and Platelets are described
on the page: Structure & Functions
of Blood.)
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6.
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| Storage of Chemical Energy |
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With increasing age some bone marrow changes from
'red bone marrow' to 'yellow bone marrow'.
Yellow bone marrow consists mainly of adipose cells, and a few
blood cells. It is an important chemical energy reserve.
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See also the related page about The
Structure and Functions of Bone (similar information to
that on this page - but in more detail;
some of the information on this page is extracted from
the main "The
Structure and Functions of Bone" page).
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