Lecture on the Skeletal System

Overview

• Focus on bone and tissue of bone, covering histology.
• Skeletal system consists of 206 bones (on average).
• Two main parts:
  • Axial Skeleton: Skull, mandible, vertebral column, thoracic cage, hyoid bone.
  • Appendicular Skeleton: Pectoral girdle, upper/lower appendages, pelvic girdle.

Types of Bones

• Long Bones: Longer than wide.
• Short Bones: Compact, relatively equal on all sides.
• Flat Bones: Thin and broad, e.g., sternum, scapula.
• Irregular Bones: No particular shape, e.g., vertebrae.
• Sesamoid Bones: Sesame seed shape, e.g., patella.
• Compact and Spongy Bone: All bones contain both types.

Bone Structure

Compact Bone

• Dense and solid.
• Made up of units called osteons.
  • Features rings of salt called Lamellae.
  • Contains Lacunae (pits) with osteocytes (bone-maintaining cells).
  • Capillaries in the Haversian Canal supply nutrients.

Spongy Bone

• Porous and light.
• Made up of trabeculae (lattice work).
  • Similar components as compact bone: Lamellae, Lacunae, osteocytes, and canaliculi.
  • Stronger in all directions due to varied trabeculae orientation.

Bone as Connective Tissue

• Composed of Matrix and Cells.

Cells of Bone

1. Osteogenic Cells: Precursor cells (mesenchymal origin).
2. Osteoblasts: Secrete the bone matrix.
3. Osteocytes: Maintain bone tissue, found in Lacunae.
4. Osteoclasts: Break down bone, derived from bone marrow.

Bone Matrix

• Organic Part: Collagen, fibers, and some sugars (provides strength).
• Inorganic Part: Calcium salts (hydroxyapatite) - provides hardness.

Forces on Bone

• Tensile Force: Bone can be stretched slightly.

• Compressional Force: Bone can be compressed.

• Torsional Force: Allows for slight twisting.

• Collagen fibers in different directions enhance support and strength.

Summary

• Bone composition: Collagen fibers with crystallized calcium salts.
• Lamellae layering in varied directions strengthens bone.
• Compact and spongy bones together provide structural integrity.