What are long bones?

Bones are a form of extremely specialized connective tissue, consisting of a mix of a dense organic matrix and inorganic mineral component. They are characterized by their hardness and mechanical resistance. Bones are segments of varying shape, size and density, all of which constitute to form the skeletal system.

Depending on their shape formations, bones can be divided into long bones, flat bones, short bones and irregular bones.  Long bones develop mainly in length (such as the femur, tibia, fibula, radius, ulna, humerus); flat bones are characterized by having higher length and width than thickness (such as bones of the skull, shoulder blades, sternum); short bones are developed in a similar way in all three dimensions (such as the carpus and tarsus); and irregular bones are characterized by not having any dominant morphological element (such as in the case of the vertebrae). Under normal circumstances, bones stop growing when an individual has reached late teens or early twenties.

Longs bones are hard, dense bones that provide structure and mobility. The femur, tibia and fibula are considered long bones in the lower limbs, and the humerus bone, ulna bone and radius bone are considered long bones in the upper limbs. The surface of long bones is covered by the periosteum, a membrane connecting the processes responsible for bone growth and callus formation in fractures. The compact bone (or cortical), which is a layer of dense bone, is located below the periosteum; and underneath the compact bone, is the location of the spongy bone (or trabecular), which contains bone marrow responsible for the production of blood cells.

A long bone has a shaft, or the central part of the bone, known as diaphysis and two ends, known as epiphysis. At the joint, the epiphysis is covered with articular cartilage, in turn forming joint surfaces. Long bones are thinner in the center and their diameter grows as the subject moves from the shaft to the epiphysis: The area between one end of the shaft and the adjacent epiphysis is known as the metaphysis. In children and adolescents, between the metaphysis and epiphysis is a cartilage, known as "conjugation", which represents the area of growth in length of this type of bones. In adults, the metaphysis is instead completely ossified.

There are two congenital disorders associated with long bones. Rachitis fetalis anularis is a disorder that occurs when the ends of the long bones (epiphyses) become enlarged. Another disorder, known as Rachitis fetalis micromelica, occurs when there is a deficiency in growth of the bones.

Calcium is an extremely important feature in an individual’s diet. Calcium intake is stored in the bones as a sort of mineral deposit, which in turn helps build stronger and healthier bones.


What function do long bones serve?

Long bones perform different functions in the human body:

  • By interacting with the muscles and tendons, they allow movement of the limbs.
  • They provide strength, structure and mobility to the upper and lower extremities.
  • They work as levers, allowing them to use their maximum potential for muscle functions (such lifting heavy objects and rapid movement).
  • Like all the other bones, they are spares and storage of minerals such as calcium, phosphorus, sodium and magnesium, essential for regulating many physiological mechanisms.
  • The bone marrow in them is capable of producing blood cells (white blood cells, red blood cells, platelets).