3B

Learning Objective

• Explain the general functions of bone.

Functions of Bones

• Bones perform several basic functions:

  • Support and Protection

  • Provide structural support and serve as a framework for the body.

  • Protect delicate tissues and organs from injury and trauma:

    • Rib cage shields the heart and lungs.
    • Cranial bones enclose and protect the brain.
    • Vertebrae enclose the spinal cord.
    • Pelvis cradles urinary and reproductive organs and the terminal end of the gastrointestinal tract.

  • Levers for Movement

  • Bones act as levers that facilitate movement by muscles, magnifying the force applied by muscles.

  • Hematopoiesis

  • Definition: Hematopoiesis (hē'ma-tō-poy-ē'sis; from haima = blood, poiesi = making) is the biological process of blood cell production.

  • Occurs in red bone marrow of spongy bone connective tissue, which contains stem cells that form blood cells and platelets.

  • The process is described in greater detail in a later section 18.3a.

  • Storage of Mineral and Energy Reserves

  • Most reserves of minerals calcium and phosphate are stored within bone connective tissue.

    • Released into the bloodstream when needed.

  • Importance of Calcium: Essential for muscle contraction, neurotransmitter release, and blood clotting.

  • Importance of Phosphate: A structural component of ATP, nucleotides, and phospholipids, important for plasma membrane structure.

  • Chemical energy is stored in the form of adipocytes (fat cells) within the shafts of some adult bones as yellow bone marrow (refer to section 7.2d).

Bone Structure and Composition

• Bones are classified as organs composed of two or more tissues:
  • Connective Tissue in bones includes:
  • Bone Connective Tissue: Comprises compact bone and spongy bone.
  • Dense Irregular Connective Tissue: Lines the inner cavity and covers the outer surface of bones.
  • Reticular Connective Tissue: Present in red bone marrow when it exists.
  • Nervous Tissue: Detects and monitors sensory stimuli about the status of the bone, which helps in perceiving pain if a bone breaks.
  • Vascularization: Bones are well vascularized with extensive blood supply for nutrients and oxygen, highlighting their dynamic nature as living organs.

Types of Bones Based on Shape

• Bones are recognized according to their shapes:

  • Long Bones

  • Greater in length than in width, characterized by an elongated cylindrical shaft (diaphysis).

  • Most common bone shape; examples include:

    • Femur (thigh bone)
    • Humerus (upper arm bone)
    • Vary in size (e.g., small long bones of fingers and much larger thigh and leg bones).

  • Short Bones

  • Length nearly equal to width.

  • Examples include the carpals (wrist bones) and tarsals (foot bones).

  • Sesamoid Bones: Small, sesame seed-shaped bones along tendons of some muscles; the largest is the patella (kneecap).

  • Flat Bones

  • Flat, thin surfaces that may be slightly curved, providing extensive surfaces for muscle attachment and protection of underlying soft tissues.

  • Examples include:

    • Roof of the skull
    • Scapulae (shoulder blades)
    • Sternum (breastbone)
    • Ribs.

  • Irregular Bones

  • Have intricate and complex shapes, not fitting into any prior categories.

  • Examples include:

    • Vertebrae
    • Hip bones (ossa coxae)
    • Several skull bones (e.g., ethmoid, sphenoid).

Conclusion

• The bones not only contribute to structural integrity and movement but also play vital roles in physiological processes such as blood formation and mineral storage, emphasizing their importance as active organs in the body.