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 (that is, 'osseous tissue', the 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
Above: Diagram illustrating the Structure of Long Bones
Above: Diagram of the Structure of Long Bones
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 this term is unfamiliar see different types of bone then return 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. 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.
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 and lacunae.- 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 referred to 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), 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
This also appears on the page about the structure and functions of bones.
(The overlap is included in consideration of the different structures of course that require this knowledge but teach it in various orders / sequences.)
- Support
The skeleton is the framework of the body, it supports the softer tissues and provides points of attachment for most skeletal muscles.
- 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.
- Assisting Movement
Skeletal muscles are attached to bones, therefore when the associated muscles contract they cause bones to move.
- 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.
- Production of Blood Cells
This process takes place in the red bone marrow inside some larger bones. Red blood cells, white blood cells and blood platelets are described on the page: Structure and functions of blood.
- 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.
For further details see also the related page about the structure and functions of bone.
