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,
- Yellow 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 channels 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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