Functions of Bone

Overview of Bone Functions

Bones are dynamic organs that perform several essential functions in the human body. These functions are critical for movement, protection, and homeostasis.

• Support: Bones provide a rigid framework that supports soft tissues and gives shape to the body.

• Protection: Bones protect internal organs from injury (e.g., the skull protects the brain, the rib cage protects the heart and lungs).

• Assistance in Movement: Bones act as levers that muscles pull on to produce movement.

• Mineral Homeostasis: Bones store minerals, especially calcium (Ca2+) and phosphorus, and release them into the blood as needed to maintain mineral balance.

• Hematopoiesis: Bones contain red bone marrow, which is the site of blood cell formation (production of red blood cells, white blood cells, and platelets).

• Triglyceride Storage: Yellow bone marrow stores triglycerides, serving as an energy reserve.

Bone Classification

Types of Bones

Bones are classified based on their shapes and functions. Each type plays a unique role in the skeletal system.

• Long Bones: Longer than they are wide; primarily found in the limbs (e.g., femur, humerus).

• Short Bones: Approximately equal in length and width; provide stability and support with little movement (e.g., carpals, tarsals).

• Flat Bones: Thin and broad; provide protection and surfaces for muscle attachment (e.g., sternum, ribs, skull bones).

• Irregular Bones: Complex shapes that do not fit other categories (e.g., vertebrae, some facial bones).

• Sesamoid Bones: Small, round bones embedded within tendons (e.g., patella).

• Sutural (Wormian) Bones: Small bones located within the sutures of cranial bones.

Structure of Bone

Gross Anatomy of Long Bones

Long bones have a characteristic structure that supports their function in movement and weight-bearing.

• Epiphysis: The expanded ends of the bone, which articulate with other bones and contain spongy bone and red marrow.

• Metaphysis: The region between the diaphysis and epiphysis; contains the epiphyseal plate (growth plate) in growing bones.

• Diaphysis: The shaft or central part of the bone, composed mainly of compact bone.

• Periosteum: A dense connective tissue membrane covering the outer surface of the bone, involved in bone growth and repair.

• Endosteum: A thin membrane lining the medullary cavity.

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

• Articular Cartilage: Hyaline cartilage covering the surfaces of the epiphyses where bones articulate, reducing friction and absorbing shock.

• Other Shapes: Flat, short, and irregular bones have a layer of spongy bone (diploë) sandwiched between layers of compact bone.

Blood and Nerve Supply of Bone

Vascularization and Innervation

Bones are highly vascularized and innervated, which is essential for their growth, repair, and function.

• Foramen: Openings in bone that allow the entry of blood vessels and nerves.

• Arteries and Veins: Bones receive blood from several sources:

  • Epiphyseal arteries and veins (supply the epiphyses)

  • Metaphyseal arteries and veins (supply the metaphyses)

  • Periosteal arteries and veins (supply the periosteum and outer compact bone)

  • Nutrient artery (enters through the nutrient foramen to supply the diaphysis and medullary cavity)

• Nerves: Accompany blood vessels and are responsible for sensing damage to bone tissue and transmitting pain signals.

Example: A fracture in a long bone can cause severe pain due to the rich nerve supply, and bleeding due to the disruption of blood vessels.