More about bones: See the Axial and Appendicular Skeleton

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Structure and Functions of Bone Tissue

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

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:

  1. A central tube called a Haversian Canal, which contains blood vessels and nerves.
    The Haversian Canal is surrounded by alternate layers of:
  2. 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.
  3. Lacunae are the small spaces between the lamellae in which contain the bone cells (called "osteocytes") are located.
  4. 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.

Support

The skeleton is the framework of the body, it supports the softer tissues and provides points of attachment for most skeletal muscles.

2.

Protection

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.

3.

Assisting in Movement

Skeletal muscles are attached to bones, therefore when the associated muscles contract they cause bones to move.

4.

Storage of Minerals

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.

5.

Production of Blood Cells

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.)

6.

Storage of Chemical Energy

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.

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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