Skeletal Materials

The main types of materials found in the skeletons of animals are chitin, cartilage and bone.

Chitin

  This is a tough, light and flexible material that is a major component of the skeletons of arthropods. It is a carbohydrate that is very similar to cellulose, the cell wall material of plants. Like cellulose, it is also freely permeable to water. Often , chitin is strengthened by deposits of hardened proteins and minerals.

Cartilage

 This tissue is found in the skeletons of complex vertebrates. It consists of living cells (chondroblasts) , and carbohydrate and protein fibres. It is a tough and flexible tissue that had great tensile strength. It acts as a shock absorber, cushioning the effect of bones moving against bones when we move. Cartilage forms the entire skeletal system of sharks and rays. In mammals there are  three types of cartilage : hyaline cartilage, fibro cartilage and elastic cartilage

Hyaline cartilage

• makes up the rings which support the trachea and bronchi and keep them open;

• covers the surface of moveable joints; and 

• supports  the protruding part of the nose.

Fibro cartilage is tougher than hyaline cartilage, and is found In the discs between the small bones (vertebrae) of the vertebral column. Elastic cartilage is present in the external ear and the epiglottis. It also supports the  Eustachian tube and the external ear canal. Cartilage does not ha e its own blood supply that depends on the oxygen and nutrient that diffuse across from nearby tissues.

Bone

This tissue is the major component of the vertebral Skeleton. It consists of living bone cells (osteocytes) , protein fibres (collagen) and minerals, mainly calcium phosphate and calcium carbonate. The minerals (non living) make up two thirds of the mass of a bone. As a result, bone is a stronger and more rigid tissue than cartilage. Bones have their own blood supply to nourish them.

    In a young vertebrate embryo, the skeleton is made up of cartilage. As the embryo grows, bone cells replace cartilage cells. This causes the cartilage tissue to harden into bone through the additions of minerals. This process is known as ossification. the embryo gets the necessary calcium compounds from the mothers blood. This, it is very important that an expectant mother eats a balanced diet containing sufficient calcium compounds. as bones continue growing after birth, a young child need to take in calcium compounds. Milk is an excellent source of calcium compounds, and should form an important part of a child diet. Vitamin D is also needed for proper bone development.

     The shape and size of a bone depend on its position and function in the vertebrate's body. The bone of the limbs are big and long,  while the three ossicles in the middle ear are small and shaped like a hammer, an anvil and a stirrup.

   The high bone of a human is a lone bone with the hollow shaft, expanded into a head at each end. The shaft is made of hard or compact bone, while the heads consists of spongy bone, while the heads consist of spongy bone covered by a thin layer of compact bone. The spongy bone has a honeycomb like appearance in section due to the presence of numerous bony struts (small bars). The hollow shaft is filled with fatty yellow marrow, while the spaces in the spongy bone contain red marrow. Many small openings in the bone allow blood vessels and nerves to enter the bony issue.

   The structures of the bone makes it both strong and light. It is often called  ' living concrete', but it is several times stronger and much higher than concrete. The protein fibres in the bone tissue, hardened by calcium salts, act as  flexible reinforcing rods, and the calcium salts act as 'cement'. The hollow structure of the long bones makes them light but does not decrease their strength in any way, I.e. a hollow long bone is nearly as strong as a solid one. The arrangement of the bony struts in the  spongy bone enables the bone to withstand great compression. The none is this ideally constructed to act as skeletal material.