Skeletal System Overview

Main Components

• Axial Skeleton: Includes skull, mandible, vertebral column, thoracic cage, and hyoid bone.
• Appendicular Skeleton: Includes pectoral girdle, upper and lower appendages, and pelvic girdle.
• Total Bones in Adults: Approximately 206 bones.

Types of Bones

• Long Bones: Longer than they are wide.
• Short Bones: Compact shape, relatively equal on all sides.
• Flat Bones: Thin, broad (e.g., sternum, scapula, parietal bones).
• Irregular Bones: No particular shape (e.g., vertebrae, ethmoid, zygomatic).
• Sesamoid Bones: Sesame seed shape (e.g., patella, pisiform).

Bone Composition

• Two Types: Spongy Bone and Compact Bone.
  • Compact Bone: Dense, made of osteons, contains lamella, lacuna, osteocytes.
  • Spongy Bone: Porous, made of trabecula, similar components as compact bone but lacks reversion canal.

Bone Cells

• Osteogenic Cells: Precursor cells that develop into osteoblasts.
• Osteoblasts: Secrete bone matrix, form osteocytes when isolated.
• Osteocytes: Maintain bone tissue, isolated in lacuna.
• Osteoclasts: Break down bone, derived from bone marrow.

Bone Matrix

• Composition: Organic (collagen fibers, elastic, and reticular fibers) and Inorganic (calcium phosphorus salts, hydroxyapatite).
• Collagen: Provides flexibility and strength.
• Calcium Salts: Crystallize on collagen, provide hardness.
• Hydroxyapatite: Combination of calcium salts.

Forces Acting on Bone

• Tensile Force: Ability to be slightly stretched.
• Compressional Force: Ability to be compressed.
• Torsional Force: Allows slight twisting.

Summary

• Bone structure and composition provide strength and flexibility.
• Osteons and trabeculae contribute to the structural integrity.
• Bone cells have specific roles in formation, maintenance, and breakdown of bone.
• The combination of collagen and calcium salts creates a balance of rigidity and slight flexibility.