Skeleton System - Bone Structure, Fracture, Conditions Affecting bone
Know your Body

The Body Anchor: Skeleton

Dr.Surya Rao Poodipeddi profile Authored by Dr.Surya Rao Poodipeddi on 18 Jan 2014 - 12:03.

The human skeleton is unique and a complex structure with a combination of several types of bones each one unique in itself either by shape, size or function. All the bones when assembled in the true form give the shape to the human body. Left to itself without the superimposed flesh, muscles and skin, the human skeleton is a horrifying sight.

Human Skeleton System

The skeleton structure: The human skeleton is a bony framework that anchors the muscles, supports the body and gives it the shape. The skeleton protects some important organs like the brain, heart and lungs. The skeleton is composed of 206 bones and is broadly divided into two parts: The Axial Skeleton and Appendicular Skeleton.


The Axial skeleton includes the skull, spine and the rib cage and consists of 80 bones. The Appendicular skeleton includes the bones of the limbs, the collar bones, the shoulder blades and the bones of the pelvis comprising of 126 bones.


The bones which form the human skeleton are of different shapes and sizes. Some of them are very small and situated inside the skull.

There are four types of bones which together form the human skeleton. They are: Long, short, flat and irregular bones. Among the long bones the femur is the longest bone measuring roughly 18 inches. Carpal bones and tarsal bones are examples of short bones. The bones of the skull and the breast bone are  examples of flat bones. The scapula and the vertebrae are examples of irregular bones. Stapes situated inside the skull is the smallest bone in the human skeleton.

The bone structure: Although bones are considerered to be very strong, it is not so strong that it cannot break. Each bone has a denser outer layer called compact bone and an inner spongy or cancellous portion. The spongy portion is a collection of honey-comb of bony supports filled with blood vessels, fat and bone marrow.

Long bones and the sternum (breast bone) are the principal source of the vital bone marrow, that manufactures red blood corpuscles.

Let us take the femur as an example to describe the structure of a long bone. It has a marrow filled cavity in its full  length surrounded by a spongy bone. The next layer is the denser compact portion. Finally the layer which covers the outer most portion of a bone is called the periosteum which contains nerves and a network of blood vessels.

The bones contain millions of cells called osteocytes which can be seen only under magnification. The osteocytes are seen in the compact bone trapped in spaces called lacunae. Osteocytes are responsible for laying down calcium that maintains the strength of a bone.

Bone Fracture: Whenever there is a break (fracture) in a bone, an intricate mechanism within, works to repair itself. A broken bone or a damaged blood vessel starts to repair and heal on its own immediately. Most of the bones when broken, take six weeks to completely heal and return to normalcy. While some bones take more time for complete recovery.

Fractures in the bones of children usually heal quickly. During a fracture which also includes damage to the blood vessel, it immediately forms a clot to seal the severed blood vessels, big or small. New soft spongy bone starts developing around the broken ends called the callus formation which helps in joining the broken ends.  This is followed by gradual replacement of the callus with a dense compact bone. Eventually the fractured bone regains its shape and its normal function over a period of time, with adequate care taken to immobilize the joints above and below the fracture site with the help of a plaster. Internal or external fixation of the fractured bone or bone grafting is done depending on the type and extent of the damage.

Conditions affecting the bone: Besides giving shape to the human body bones also serve as a reservoir for several minerals like calcium and phosphorus. The commonest conditions affecting a bone are the fractures and dislocations of the joints between bones mainly due to falls and accidents. Other conditions affecting bones include congenital malformations like additional bones, absence of bones and nonunion of flat bones etc. Cancer of a bone is not uncommon and sarcoma is an example.Osteoporesis is a condition affecting mostly women and is common in post-menopausal women due to inadequate intake of calcium.

*Disclaimer: This is not medical advice. The content is for educational purposes only. Please contact your doctor for any health care issues.