Overview of the Skeleton: Structure of Bones

Gross Anatomy of the Typical Long Bone

The long bones are essential components of the human skeleton, providing support, movement, and protection. Their structure is specialized to accommodate growth, blood cell formation, and mineral storage. Understanding the anatomy of a typical long bone is fundamental in anatomy and physiology.

• Long Bone: A bone that is longer than it is wide, typically found in the limbs (e.g., femur, humerus).

• Diaphysis: The shaft or central part of a long bone.

• Epiphysis: The ends of a long bone, usually broader than the diaphysis.

• Epiphyseal Line: Remnant of the epiphyseal plate, marking the site of bone growth during childhood and adolescence.

• Periosteum: Dense connective tissue membrane covering the outer surface of bones, except at joints.

• Endosteum: Thin membrane lining the medullary cavity inside the bone.

• Medullary Cavity: Central cavity within the diaphysis, containing bone marrow.

• Articular Cartilage: Smooth, white tissue covering the ends of bones where they form joints, reducing friction.

• Red Marrow: Hematopoietic tissue found in certain bones, responsible for blood cell formation.

• Yellow Bone Marrow: Fatty tissue found in the medullary cavity of adult bones.

Key Functions and Structures

• Support: Long bones provide structural support for the body.

• Movement: Serve as levers for muscles to act upon.

• Protection: Protect vital organs (e.g., skull protects brain).

• Blood Cell Formation: Occurs in red marrow within certain bones.

• Mineral Storage: Bones store calcium and phosphorus.

Major Parts of a Long Bone

• Diaphysis: The elongated shaft, composed mainly of compact bone.

• Epiphyses: The expanded ends, consisting of spongy bone covered by compact bone.

• Articular Cartilage: Covers joint surfaces, providing smooth movement.

• Periosteum: Outer fibrous layer, contains blood vessels and nerves; essential for bone growth and repair.

• Medullary Cavity: Central cavity containing yellow marrow in adults.

• Endosteum: Lines the medullary cavity and spaces within spongy bone.

• Epiphyseal Line: Marks the location of the growth plate, which allows for lengthwise bone growth during development.

Table: Key Structures and Their Functions

Microscopic Anatomy of Bone: Osteon Structure

The osteon (or Haversian system) is the fundamental functional unit of compact bone. It consists of concentric layers of calcified matrix and associated cells, providing strength and facilitating nutrient exchange.

• Lamella: Layer of bony matrix around a central canal.

• Lacuna: Small cavity containing an osteocyte.

• Central Canal (Haversian Canal): Longitudinal canal carrying blood vessels, lymphatics, and nerves.

• Canaliculi: Tiny canals connecting osteocytes within an osteon, allowing for nutrient and waste exchange.

Table: Osteon Components and Functions

Additional info:

• Osteoprogenitor Cells: Stem cells found in the endosteum and periosteum, responsible for bone growth and repair.

• Spongy Bone: Found mainly in the epiphyses, contains trabeculae and red marrow.

• Compact Bone: Dense outer layer providing strength and protection.

• Growth Plate (Epiphyseal Plate): Region of hyaline cartilage where bone growth occurs in children and adolescents.

Relevant Equations

• Bone Density:

• Osteon Arrangement: