Lecture 2.3 and 2.4

Lectures Overview

• Course Title: Composition and Organization of Bone

• Instructor: Tim Maley, PhD

• Contact Information: Email: maleytim@arizona.edu | Office: Gittings 113

Objectives of Lectures 2.3 & 2.4

1. Components of Bone as a Connective Tissue

   • Understand different cell types and extracellular components.

2. Extracellular Matrix of Bone

   • List components and explain their contributions to bone strength.

3. Cell Types in Bone

   • Describe functions of the four cell types found in bone.

4. Bone Remodeling

   • Discuss major steps and purpose of bone remodeling.

5. Differences Between Compact and Spongy Bone

   • Examine location, function, and composition.

6. Microscopic Structure of Compact Bone

   • Understand the osteon structure and its organization.

Composition of Bone

• Osteology: Study of bone tissue.

• Major Components:

  • Connective Tissue: Composed of cells, fibers (collagen), and ground substance.

Cells in Bone

• Osteogenic Cells: Stem cells that develop into osteoblasts.

• Osteoblasts: Build bone by forming the bone matrix (synthesize collagen).

• Osteocytes: Maintain bone tissue, respond to damage and stress.

• Osteoclasts: Breakdown bone matrix (bone resorption).

Osteogenic Cells

• Function:

  • Bone stem cells differentiated from mesenchyme.

  • Found in periosteum and endosteum.

• Process:

  • Undergo mitosis leading to differentiation into osteoblasts.

Osteoblasts

• Role:

  • Responsible for bone formation by synthesizing collagen and initiating calcification.

• Key Point:

  • Immature bone cells that deposit calcium into the matrix via exocytosis.

Osteocytes

• Description:

  • Mature bone cells involved in bone tissue maintenance.

• Functions:

  • Sense microdamage and mechanical forces, trigger repair processes.

Osteoclasts

• Function:

  • Responsible for bone resorption and degradation of the bone matrix.

• Process:

  • Release proteolytic enzymes and acids, derived from myeloid stem cells.

Bone Remodeling

• Process:

  • Involves resorption of old bone by osteoclasts and formation of new bone by osteoblasts.

• Goal of Remodeling:

  • Achieve strength while maintaining lightness and remove damaged bone to maintain overall strength.

Steps in Bone Remodeling

1. Activation: Preosteoclasts stimulated to differentiate.

2. Resorption: Osteoclasts digest mineral matrix.

3. Reversal: End of resorption, recruitment of osteoblasts.

4. Formation: Osteoblasts synthesize new bone matrix.

5. Quiescence: Osteoblasts become resting bone-lining cells.

Composition of Bone Extracellular Matrix

• Organic Components:

  1. Ground Substance:

     • Contains glycosaminoglycans (GAG) and glycoproteins.

  2. Collagen Fibers:

     • Type I collagen, resistant to pulling forces, provides flexibility.

• Inorganic Components:

  1. Water: Essential for matrix composition.

  2. Hydroxyapatite: Major mineral component providing structure and rigidity.

Comparison of Spongy and Compact Bone

• Spongy Bone:

  • Structure: Irregular lattice of thin plates (trabeculae).

  • Function: Lightens skeleton, provides strength from multiple directions, contains red marrow.

• Compact Bone:

  • Structure: Solid network organized into osteons.

  • Function: Provides longitudinal strength and structural support to long bones.

Structural Organization in Bones

• Osteon: Functional unit of compact bone, consisting of concentric lamellae around a central canal.

• Trabeculae: Framework of spongy bone supporting the bone structure within marrow cavities.

Skeletal Disorders Related to Bone Composition

• Rickets:

  • Caused by calcium deficiency (lack of vitamin D). Leads to flexible bones.

• Scurvy:

  • Result of collagen synthesis problems due to vitamin C deficiency. Results in brittle bones.

Suggested Learning Activities

• Create diagrams illustrating bone structure and functions of different cell types.

• Draw flow charts to depict processes of bone remodeling and collagen organization in compact vs. spongy bone.