Your Bones!!! What is functions?

The skeletal system is a complex and multi-functional system. Its main functions are:

a.Support -Bone is the major supporting tissue of the body. It is a strong tissue that can support huge quantities of weight, and can be considered the load bearing foundation of our bodies. In addition to bone, cartilages provides a firm but flexible support in some structures such as our trachea, while ligaments attach to bones and help to join bones together and hold them firmly.

b.Movement-Our movement is achieved through the cooperative function of our muscles and our bones. Muscles are attached to bones by tendons, and through the presence of joints, allow for the movement of our limbs.

c.Protection -Bone is hard and firm, and is vital as a protective tissue for our most important organs. The skull surrounding and protecting the brain is the best example of bone performing such a function. Another example is the rib cage which surrounds and protects the heart and the lungs, as well as the other organs of our thorax.

d.Storage -The bones of the skeletal system also play a vital role in storage of certain minerals in our bodies. The most important minerals stored by the bones are calcium and phosphorus. Bones also store a small quantity of fat.

e.Production of blood cells -Some bones have cavities containing bone marrow which is a specialised tissue that gives rise to blood cells and platelets.

Bone Tissue
Adult bones are normally about 65% inorganic material and 35% organic material by weight. The inorganic material is primarily a calcium phosphate crystal called hydroxyapatite whose chemical formula is Ca10(PO4)6(OH)2. The organic material is primarily collagen and proteoglycans. The collagen and the mineral components are the ones responsible for the functional characteristics of bones.

Bone tissue is generally divided into an extracellular bone matrix and bone cells:

i.Bone Matrix
-The bone matrix can be thought of as having the same functional structure as steel reinforced concrete. Collage fibres give the bone flexible strength like the steel bars in reinforced concrete, while the mineral component gives bones their compression (weight-bearing) strength just like the concrete in reinforced concrete. Without collage, bones become too brittle, and without hydroxyapatite, bones become too flexible.

ii.Bone Cells
-There are three types of bone cell, namely osteoblasts, osteocytes, and osteoclasts. These have different functions and origins.
#Osteoblasts produce the mineralised bone matrix through a process called ossification (or osteogenesis). Osteoblasts produce collage and proteoglycans and accumulate calcium and phosphorus ions. All these substances are released from the cell, and through the action of enzymes, hydroxyapatite crystals are formed that accumulate to form the bone matrix.
#Osteocytes are mature bone cells. Once an osteoblast is surrounded by the bone matrix, it becomes relatively inactive and is termed an osteocyte. Within the bone matrix, osteocytes occupy a space called lacunae, and extend processes called calculi into the bone matrix. It is around this cellular framework that the bone matrix develops.
#Osteoclasts are large specialised bone cells that are responsible for the breakdown or resorption of bone.

Bone tissue is classified according to the way bone tissue is laid down in the bone matrix into two classes of bone:

#Woven bone has collage fibres oriented randomly in several directions. It is formed early in bone development during our fetal stage, and is later remodelled into lamellar bone.
#Lamellar bone is mature bone. It is built of thin layers called lamellae. In each lamellae, collagen fibres are arranged parallel to one another.

Regardless of the arrangement of bone tissue (woven or lamellar), bones are classified according to the amount of space in relation to the amount of bone matrix within the bone. There are two classes of bones ;
#Cancellous bone has less bone matrix and more space. It is lighter than compact bone and, because of its sponge-like appearance, is sometimes referred to as spongy bone.
#Compact bone has more bone matrix and less space. It is denser and stronger than cancellous bone.

Bone Shapes-Bones are classified into four groups according to their shape, namely long bones, short bones, flat bones, and irregular bones.

Long bones-Long bones are longer than they are wide. The best examples of long bones are the bones of the upper and lower limbs. A long bone will have three major sections :

#Diaphysis, or the shaft, that is composed primarily of compact bone,

#Epiphysis which is the end of the bone, and is composed primarily of cancellous bone, and is covered in articular cartilage if it forms a joint,

#Epiphyseal plate is the section of the bone where growth in length occurs, and is also called the growth plate. It is located between the diaphysis and the epiphysis and is composed of hyaline cartilage. When a bone has stopped growing, the epiphyseal plate becomes ossified and forms the epiphyseal line.

Short bones -Are usually as wide as they are long. The bones of the wrist (carpals) are a good example of short bones. They have no diaphyses but may have small epiphyses. They are similar in composition to the epiphyses of long bones.

Flat bones -Are thin and narrow and are often curved. Examples of flat bones are some of the skull bones and the ribs. Flat bones usually have no diaphyses or epiphyses. They are built as a sandwich of cancellous bone sandwiched between two layers of compact bone.

Irregular bones -Have a variety of shapes that cannot be classified into any of the groups above. Examples include the vertebrae and the facial bones. They have no diaphyses but may have small epiphyses. They are similar in composition to the epiphyses of long bones.
The flat and irregular bones of the skull often contain air filled spaces called sinuses.