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Bone Structure And Function

Discover the fascinating link between bone structure and function, unraveling the secrets behind how our bodies are built to support and thrive.

USMLE Guide: Bone Structure and Function


The purpose of this guide is to provide an overview of bone structure and function, which is a key topic for the United States Medical Licensing Examination (USMLE). The article "Bone Structure and Function" explores the intricate details of bones, their composition, and the vital roles they play in the human body.

Key Concepts

  1. Composition of Bones

    • Bones are composed of two main components: organic and inorganic.
    • Organic components include collagen fibers, which provide flexibility and tensile strength.
    • Inorganic components consist of hydroxyapatite crystals, primarily composed of calcium and phosphate, providing rigidity and strength.
  2. Bone Cells

    • Osteoblasts: Responsible for bone formation, they secrete collagen and other organic components.
    • Osteoclasts: Involved in bone resorption, they break down and remodel existing bone tissue.
    • Osteocytes: Mature bone cells that maintain bone health and regulate mineral homeostasis.
  3. Bone Types

    • Long Bones: Longer than they are wide, such as the femur and humerus.
    • Short Bones: Approximately equal in length and width, e.g., carpals and tarsals.
    • Flat Bones: Thin, flat, and often curved, such as the skull bones.
    • Irregular Bones: Unique shapes, like the vertebrae and facial bones.
  4. Bone Microstructure

    • Compact Bone: Dense and solid outer layer of bone, providing strength and protection.
    • Spongy (Cancellous) Bone: Honeycomb-like structure found within compact bone, responsible for metabolic activities and bone marrow production.
  5. Bone Growth and Remodeling

    • Longitudinal Growth: Occurs at the epiphyseal plates, where cartilage is replaced by bone.
    • Appositional Growth: Bone thickening and widening through the addition of new layers on the outer surface.
    • Bone Remodeling: Constant process involving the removal of old bone by osteoclasts and replacement by osteoblasts.
  6. Bone Functions

    • Support: Provides structural framework for the body, protecting organs and enabling movement.
    • Protection: Shields vital organs from potential damage.
    • Hematopoiesis: Occurs in the bone marrow, where blood cells are produced.
    • Mineral Storage: Stores minerals like calcium and phosphate, essential for various physiological processes.
    • Acid-Base Homeostasis: Buffers blood pH by releasing or absorbing alkaline salts from bones.

Clinical Significance

Understanding bone structure and function is crucial in diagnosing and managing various conditions and diseases, including:

  • Osteoporosis: Characterized by decreased bone density and increased fracture risk.
  • Osteomalacia: Softening of bones due to vitamin D deficiency or impaired metabolism.
  • Fractures: Understanding bone structure aids in assessing fracture severity and determining appropriate treatment.
  • Bone Cancer: Knowledge of bone composition assists in diagnosing and treating bone tumors.


This USMLE guide has provided an overview of bone structure and function, covering key concepts such as bone composition, types, microstructure, growth, and functions. It is essential to grasp these concepts to excel in the USMLE and to apply this knowledge in clinical practice for diagnosing and managing bone-related conditions.

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