Functions of the Bones

Overview of Bone Functions

Bones are essential organs of the skeletal system, providing multiple critical functions for the human body. Their structure and composition allow them to support, protect, and facilitate movement, as well as serve as reservoirs for minerals and sites for blood cell formation.

• Support: Bones form the framework that supports the body and maintains its shape.

• Protection: Bones protect vital soft organs. For example:

  • The skull and vertebrae protect the brain and spinal cord.

  • The rib cage protects organs in the thoracic cavity, such as the heart and lungs.

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

• Storage: Bones store minerals (especially calcium and phosphorus) and fats (in the internal marrow cavity).

• Blood Cell Formation (Hematopoiesis): The process of forming blood cells occurs in the bone marrow.

Classification of Bones

Types of Osseous Tissue

The adult human skeleton consists of 206 bones, which are composed of two main types of osseous (bone) tissue: compact bone and spongy bone.

• Compact Bone:

  • Dense, smooth, and homogeneous in texture.

  • Provides strength and structure.

• Spongy Bone:

  • Composed of small, needlelike pieces of bone called trabeculae.

  • Contains many open spaces, which are often filled with marrow.

Structure of Flat Bones

Flat bones, such as those in the skull, consist of a layer of spongy bone sandwiched between two thin layers of compact bone. This arrangement provides both protection and a lightweight structure.

• Example: The cranial bones protect the brain while remaining relatively light.

Structure of Bone

Long Bone Anatomy

Long bones, such as the humerus, have a specialized structure that supports their function in movement and strength.

• Diaphysis (Shaft):

  • Makes up most of the bone’s length.

  • Composed of compact bone for strength.

• Periosteum:

  • Outer covering of the diaphysis.

  • Consists of a fibrous connective tissue membrane.

  • Perforating (Sharpey’s) fibers secure the periosteum to the underlying bone.

Internal Structure of Long Bones

The internal anatomy of long bones includes several key features that contribute to their function and maintenance.

• Endosteum: Lines the inner surface of the shaft; made of connective tissue.

• Medullary Cavity:

  • Central cavity inside the shaft.

  • Contains yellow marrow (fat storage) in adults.

  • Contains red marrow (site of hematopoiesis) in children up to age 6 or 7.

• Nutrient Arteries: Supply blood to bone tissue.

Epiphysis and Articular Cartilage

The ends of long bones are called epiphyses and are crucial for joint formation and movement.

• Epiphysis:

  • Composed mostly of spongy bone, enclosed by a thin layer of compact bone.

• Articular Cartilage:

  • Covers the external surface of the epiphyses.

  • Made of hyaline cartilage.

  • Decreases friction at joint surfaces, facilitating smooth movement.

Additional info:

• The epiphyseal line is a remnant of the epiphyseal plate, which is responsible for lengthwise growth in young bones.

• The periosteum and endosteum are essential for bone growth, repair, and nutrition.