Structure of skeletal tissues
All tissues which make up the skeletal system consist of cartilage and bone.
This tissue is soft and slightly elastic. It consists of cells known as chondrocytes, which forms a matrix of chondrin (a gelatinous protein) and exists within small spaces called lacunae. Cartilage is avascular – it does not possess a blood supply and receives nutrition by diffusion from the capillary network outside the cartilaginous tissue.
In the developing foetus, all bones start out as cartilage, and is gradually replaced by bone (see page below).
There are three basic types of cartilage found in the body:
- Hyaline (articular) cartilage: this is a fairly resilient tissue, and is found on the end surfaces of all bones that meet to form joints (articulations). It is bluish-white in colour and is composed of a matrix of collagen fibres. Its function is to protect the bone tissue from wear and tear and to reduce friction between articulating bones. Moving a joint helps to increase nutrients supplied to this tissue and can aid growth. Exercise, therefore, often helps to thicken cartilage and further protects the joints. It also forms the costal cartilages, which attach the ribs to the sternum, as well as being found in the larynx, trachea and bronchi.
- White fibrocartilage: this is a much denser tissue than hyaline cartilage and consists of a dense mass of white fibres in a solid matrix, with the cells spread thinly among the fibres. It is very tough and acts like a shock absorber. It is, therefore, often found in areas of the body where high amounts of stress are imposed. Examples include the semi-lunar cartilages of the knee joint, the intervertebral discs, and it surrounds the rim of the bony sockets of the hip and shoulder joints.
- Yellow elastic cartilage: this consists of yellow elastic fibres which run through a solid matrix, with cells lying between the matrix. This is a much more pliant and flexible tissue and gives support and flexibility. Examples include the ear lobe and the epiglottis.