Bones and Skeletal Tissues

Functions of Bones

Bones are essential organs of the skeletal system, providing multiple functions necessary for human physiology and movement.

• Support: Bones form the framework that supports the body and cradles soft organs.

• Protection: Bones provide a protective case for the brain, spinal cord, and vital organs.

• Movement: Bones act as levers for muscles, enabling movement.

• Mineral Storage: Bones serve as reservoirs for minerals, especially calcium and phosphorus, which are essential for various cellular processes.

• Blood Cell Formation: Hematopoiesis, the formation of blood cells, occurs within the marrow cavities of bones.

Gross Anatomy of Bones

Bone Textures

Bones are composed of two main textures, each with distinct structural and functional properties.

• Compact Bone: The dense outer layer of bone that provides strength and protection.

• Spongy Bone: Also known as cancellous bone, it consists of a honeycomb of trabeculae filled with yellow or red bone marrow.

Structure of Long Bone

General Structure

Long bones, such as the femur and humerus, have a characteristic structure that supports their function in movement and support.

• Diaphysis: The tubular shaft that forms the axis of long bones. It is composed of compact bone that surrounds the medullary cavity.

• Medullary Cavity: The central cavity within the diaphysis, containing yellow bone marrow (fat) in adults.

• Epiphyses: The expanded ends of long bones. The exterior is compact bone, while the interior is spongy bone. The joint surface is covered with articular (hyaline) cartilage to reduce friction and absorb shock.

Illustration of Long Bone Structure

The following table summarizes the main anatomical regions of a long bone:

Key Terms

• Articular Cartilage: Hyaline cartilage covering the joint surfaces of epiphyses, providing smooth movement at joints.

• Periosteum: A double-layered membrane covering the external surface of bones, rich in blood vessels and nerves.

• Endosteum: A thin membrane lining the internal surfaces of bone, including the medullary cavity.

Example: Femur Anatomy

The femur, a typical long bone, consists of a diaphysis (shaft), two epiphyses (ends), a medullary cavity filled with yellow marrow, and is covered externally by the periosteum and internally by the endosteum.

Additional info: The structure of long bones is crucial for their function in weight-bearing and movement. The arrangement of compact and spongy bone allows for both strength and lightness, while the presence of marrow cavities supports hematopoiesis and fat storage.