What is a bone?

Bone is a dense type of connective tissue impregnated with inorganic salts mainly the salts of calcium such as calcium phosphate, calcium carbonate etc. The organic portion of the bone constitutes one third (1/3) and the inorganic salt component constitutes two third (2/3). The inorganic salts are mainly responsible for rigidity and hardness, which make bone resist compression caused by the forces of weight and impact. The organic connective tissue portion of the bone makes it resilient and thus the bone can afford resistance to tensile forces. In strength bone is comparable to iron and steel.

Bone forms an important component of the skeleton of human body. Because of its rigidity and hardness, it provides the strength and form necessary to keep human body in its shape. It also protects the delicate organs vital for life, for example the skull protects the brain and the ribcage protects heart and lungs.

Bone (femur)

Bone (Femur)

Types of bones:

The detail of different types of bones is a huge topic and that is why it could not be explained here. Please visit “Types of bones” for studying complete classification.

Basic Structure of an adult long bone:

A typical long bone of adult human beings consists of the following important parts.
It is the long middle part of an adult human long bone. It is composed of periosteum, cortex and a medullary cavity from outside to inside.
Periosteum is thick fibrous membrane covering the surface of the bone. The periosteum is composed of two layers; an outer fibrous layer and an inner osteogenic (bone producing) cellular layer. This attachment of bone and the periosteum is specifically strong over the attachments of tendons and ligaments.
The cortex is actually the compact part of the long bone. The strength of the bone which makes it capable to withstand all the stresses is mainly due to this cortex. In the cortex the ratio of bone substance to bone spaces is a large quantity.
The medullary cavity is the central portion of a long bone that is filled with red or yellow bone marrow. At the time of birth the bone marrow is red every where and hemopoeisis is very active in this marrow but as a person gets older, the red marrow is replaced by yellow marrow that is fatty in nature and has no power of hemopoeisis (Blood cell production). At this level of age the red marrow persists only at the cancellous (spongy) ends of a long bone.
The ends of long bone are actually not compact as the shaft. They are made up of spongy (cancellous) bone. In cancellous bone the bone substance to bone spaces ratio is a smaller quantity. This means that there is little bony tissue and more empty spaces in this portion of the bone.

Basic structure of an adult long bone

Basic structure of an adult long bone

Blood Supply of Bones:

Bones receive blood supply from a number of different sources, all of which have their own importance. The sources include Nutrient artery, Epiphyseal arteries, Periosteal arteries and Metaphyseal arteries. Visit Blood Supply of Bones for complete detail.

Nerve Supply of bones:

Most of the nerves coming to bones are sympathetic and vasomotor in function. Furthermore, bones form important sensory organs of the body to provide useful information to the Central Nervous System. Visit Nerve Supply of Bones for complete details.