Anatomy: skeletal system

Anatomy: skeletal system

Bones are classified according to their shape, and are categorised as either long, short, flat or irregular.

  • Long– longer than they are wide eg femur
  • Short– the same length as width eg patella or carpal bones
  • Flat– flattened width bones eg ribs or skull
  • Irregular– bones that don’t fit into any other category and connect other bones together eg pelvis
  • Sesamoid are a type of irregular bone that fit around or between tendons eg pisiform bone in the wrist carpals
otter skeleton.jpg
Not a human skeleton.

The functions of bones in the human body are to support, protect organs, provide levers for movement, to produce blood cells and to provide posture.


A typical long bone has epiphysis at either end which is the rounding where it meets another bone. The main shaft is called the disphysis. At one end near the epiphysis is the epiphyseal plate where new bone is grown. The shaft of the bone consists of dense, strong compact bone on the outside and spongy bone which has lots of holes for the marrow on the inside. The marrow is contained in the medullary cavity in the middle of the bone. Throughout the bone there are gaps for blood vessels to flow through.

At the epiphyseal plates, which are located at one end of the bone, new bone growth occurs. Here non-specialsed osteoprogenitor cells become osteoblast cells. These cells surround themselves with a matrix of calcium minerals to become final bone cells or osteoclytes. The minerals calcium and phosphorous mainly make up bone.

Because calcium is needed for new bone growth it is important for children and adults to get enough in their diet, since bone renewal occurs throughout someone’s life. Weight bearing exercise like running or weight lifting also increases the amount of compact bone in someone’s body and increases the strength of their bones compared to someone who doesn’t exercise.


Where two bones meet they form a joint. The joints on the human body can be either:

  • Ball and socket eg hip
  • Hinge eg elbow or knee
  • Pivot eg forearm or neck
  • Condyloid (gliding) eg metacarpal-phalanges aka your knuckles
  • Saddle eg thumb



Colbert B, Ankney J, Lee KT (2012) Anatomy and Physiology for Health Professionals Florida: Jones and Bartlett Learning