Bone Histology Overview

Bone Histology

• Bone is a highly vascular specialized connective tissue
• Matrix is calcified, making it hard and supporting body weight
• Composed of three main components: bone cells, fibers, and hard matrix
• Anatomical classifications: long (e.g., humerus, femur), short (e.g., carpal, tarsal), flat (e.g., skull, ribs), and irregular (e.g., vertebrae)
• Functions: support, protection, movement, mineral storage, and blood cell formation

Learning Objectives

• Classify bones anatomically and histologically
• Locate compact and spongy bones in the human body
• Understand bone microstructure

Histological Classification

• Compact bone: dense, solid lamellae without cavities
  • Located in the shaft surrounding the medullary canal and covering flat, short, and irregular bones
• Cancellous (spongy) bone: irregular branching, anastomosing bony trabeculae
  • Located in the center of flat bones, short bones, irregular bones, and the epiphysis of long bones

Bone Structure

• Bone cells:

  • Osteogenic cells (osteoprogenitor cells):
  • Osteoblasts (bone-forming cells), producing osteoid tissue (organic part)
  • Osteocytes (bone-maintaining cells): mature bone cells maintaining bone hardness, residing in lacunae
  • Osteoclasts: large, multinucleated cells
    • Resorb bone by releasing H+ ions and lysosomal enzymes
    • Located in Howship's lacunae, shallow depressions near resorbing surfaces

• Fibers (mainly collagen type I): organic part (35%) of the matrix

• Ground substance: mostly GAGs and glycoproteins (without water). It's where hydroxyapatite is deposited

• Hydroxyapatite crystals: inorganic part (65%)

  • Calcium salts (Ca phosphate and hydroxide) deposited on collagen fibers
  • Calcify the matrix

Histology of Compact Bone

• Layers from outward to inward:
  • Periosteum
  • External circumferential lamellae
  • Haversian system (osteon)
  • Interstitial lamellae
  • Internal circumferential lamellae
  • Endosteum

Histology of Spongy Bone

• Irregular branching, anastomosing bony trabeculae
• Trabeculae contain bone lamellae, osteocytes, but no osteons
• Enclose bone marrow cavities

Explore the intricate details of bone histology, from its composition to classifications. This quiz will help you understand the anatomy of different bone types and their unique functions within the body. Get ready to classify and locate various types of bones and comprehend their microstructure.