The skeletal system includes bone and cartilage. In an adult human, there are approximately 206 bones and these have the functions of supporting the body and muscles, protecting and enclosing visceral organs, helping us to move, making blood, and providing a place to store minerals and salts. The skeletal system is clearly absolutely essential for us to survive, so what are its components and how do they work?
First of all, we need to be able to classify each bone under a general heading. There are long bones (for example arm and leg bones), short bones (eg. carpals and tarsals), flat bones (cranial bones, sternum, ribs), irregular bones (eg. vertebrae) and other bones (eg. preumatic, sesamoid and accessory). Each bone contains osteoblasts which produce bone cells, and osteoclasts which dissolve bone cells.
In a long bone for instance, the periosteum is the outer layer surrounding the bone (except at the joint surfaces because they are covered with cartilage). Then as you go inside the bone, you reach compact bone, then spongy bone. Within this, is the diaphysis – a shaft of bone and inside this structure is the medullary cavity. In this cavity, bone marrow is formed and nutrients are delivered through the nutrient foramen – a small opening where blood vessels are able to enter and exit the bone. Near the middle of the diaphysis is the primary centre of ossification and this where the bone will grow from.
Bones would not be much good at helping us move without the presence of cartilage. There are three types of cartilage – hyaline, fibrocartilage and elastic cartilage. Hyaline cartilage is present as a covering over articular surfaces. It has a glassy appearance and allows bone to glide against bone. Fibrocartilage, on the other hand, forms discs. It is dense and acts as a shock absorber. Elastic cartilage is made of elastic fibres and has flexibility. It makes up the ear, auditory tube and parts of the larynx. It is difficult to regenerate cartilage, and if damaged it is sometimes removed.
Although strong, bones can be broken as is seen commonly in children. In adults, the bones are usually stronger than the ligaments, however for children this situation is reversed which is why it is quite a normal sight to see a child with a cast in a primary school. A simple fracture is where the bone breaks but is not exposed to air, however if the bone pierces the skin and sticks out, it is called a compound fracture and has the potential to become infected. The healing process of fractures occurs more rapidly in children. Also, non-weight-bearing bones heal faster than weight-bearing ones.
The skeletal system is complex yet brilliant in the way all bones fit together to make a skeleton capable of doing many different things. The body has solutions to all problems – cartilage stops bone grinding on bone, the nutrient foramen allows a point of entry to an otherwise enclosed cavity, the centres of ossification allow growth and so on. Even though the skeletal system can be damaged, it can also be repaired so movement can continue.