Structure of Bones
Introduction
Bones form the framework of the human body and serve as a crucial component of the skeletal system. They provide support, protect vital organs, enable movement by acting as levers for muscles, and house bone marrow, which produces blood cells. Bones are made of a hard matrix primarily composed of calcium phosphate and collagen fibers.
Classification of Bones
Bones are classified based on their shape and function:
1. Long Bones:
o Found in the limbs, long bones like the femur and humerus are cylindrical in shape and function as levers for movement. They have a diaphysis (shaft) and two epiphyses (ends).
2. Short Bones:
o Short bones, such as those found in the wrists (carpals) and ankles (tarsals), are cube-shaped and provide stability with some movement.
3. Flat Bones:
o Flat bones, like the sternum, ribs, and scapula, provide protection for vital organs and surfaces for muscle attachment.
4. Irregular Bones:
o Bones with complex shapes, such as the vertebrae and some facial bones, are classified as irregular bones.
5. Sesamoid Bones:
o Sesamoid bones, like the patella, are embedded within tendons and help reduce friction during movement.
Structure of Bone Tissue
1. Compact Bone:
o Compact bone is the dense, outer layer of bone that provides strength and rigidity. It consists of closely packed structural units called osteons or Haversian systems. Each osteon contains a central canal surrounded by concentric rings of bone matrix called lamellae. Blood vessels and nerves run through the central canal, supplying the bone cells.
2. Spongy Bone:
o Spongy bone (also called cancellous bone) is lighter and less dense than compact bone. It consists of a network of trabeculae, which are thin bony plates that provide structural support. Spongy bone is found at the ends of long bones and in flat bones. It contains red bone marrow, which is responsible for producing blood cells.