Chapter 6: Skeletal System Study Notes

Chapter 6: Skeletal System Overview

Introduction

  • Importance of the Chapter: Understanding the skeletal system, including how bones are made and function.

  • Main Topics: Bone growth, formation types, fractures, bone classification, and skeletal structure.

Bone Growth

  • Growth in Height: Achieved through the growth plate.

  • Growth in Width: Provides strength and stability.

  • Growth Plate: Contains cartilage, allows for growth until adulthood.

Classification of Bones

  • Total Bones in the Skeleton: 206.

  • Bone Shapes:

    • Long Bones

    • Short Bones

    • Flat Bones

    • Irregular Bones

    • Sesamoid Bones (e.g., patella).

Skeleton Structure

  • Axial Skeleton: Comprises vertebrae (about 31), ribs (12 pairs), sternum, cranial (skull), and facial bones (22).

  • Appendicular Skeleton: Includes arms (pectoral girdle: clavicle, scapula) and legs (pelvic girdle: ilium, ischium, pubis).

Types of Cartilage

  • Hyaline Cartilage:

    • Location: Rib cage, nose, ends of long bones.

  • Elastic Cartilage:

    • Location: Epiglottis, outer ear (pinna).

  • Fibrocartilage:

    • Location: Pubic symphysis, menisci of knee, intervertebral discs.

Cartilage Growth

  • Types of Growth:

    • Appositional Growth: Increase in width (cartilage forming cells in perichondrium secrete matrix on existing cartilage).

    • Interstitial Growth: Increase in length (chondrocytes divide and secrete matrix from within).

  • End of Cartilage Growth: Terminates in the early 20s when growth plates become lines.

Functions of Bones

  • Support: Maintain structure and support soft organs.

  • Protection: Protect major organs (e.g., ribs protect lungs and heart, skull protects brain).

  • Movement: Bones act as levers for muscle action.

  • Mineral Storage: Reservoir for calcium and phosphorus (most important minerals).

  • Blood Cell Production: Hematopoiesis occurs in red marrow of bones.

  • Energy Storage: Yellow marrow for triglyceride fat storage.

  • Hormone Production: Osteocalcin regulates glucose levels and metabolism.

Bone Classification (by Shape)

  • Long Bones: Longer than wide (e.g., humerus, femur, metacarpals, phalanges).

  • Short Bones: Typically cube-shaped (e.g., tarsals, carpals).

  • Flat Bones: Thin, flat (e.g., ribs, sternum, scapula).

  • Irregular Bones: Complex shapes (e.g., vertebrae, pelvic bones, most facial bones).

  • Sesamoid Bones: Form in tendons (e.g., patella).

Bone Anatomy

  • Structure of Long Bones:

    • Diaphysis: Long shaft.

    • Epiphyses: Ends of the bone.

    • Periosteum: Outer layer that contains blood vessels and nerves.

    • Endosteum: Inner layer lining the medullary cavity.

    • Medullary Cavity: Contains yellow marrow.

    • Spongy Bone: Found at epiphyses, where red marrow is located.

Compact Bone Structure

  • Basic Unit: Osteon (Haversian system).

    • Central Canal: Contains blood vessels and nerves.

    • Perforating Canals: Connect central canals.

    • Canaliculi: Tiny channels for communication between osteocytes.

  • Lamellae: Rings of calcified matrix in osteons.

  • Sacrificial Bonds: Help dissipate energy and prevent fractures during stress.

Spongy Bone Structure

  • Trabecular Bone: Organized along lines of stress, no osteons.

  • Osteocytes and Canaliculi: Communicate nutrients and waste.

Chemical Composition of Bones

  • Organic Components: Bone cells and osteoid (collagen and ground substance).

  • Inorganic Components: Mineral salts (calcium phosphate) make bones hard and resist compression.

  • Bone Strength: 50% as strong as steel for compression, 100% for tension.

Bone Development

  • Ossification: Starts at two months of development.

  • Types of Ossification:

    • Endochondral: Long bones replace hyaline cartilage.

    • Intramembranous: Flat bones develop from fibrous membranes.

Bone Growth Mechanisms

  • Interruption of Growth: Happens at epiphyseal plate—5 zones (resting, proliferating, hypertrophic, calcification, ossification).

  • Hormonal Regulation: Growth hormone, thyroid hormones, testosterone, and estrogen all influence growth.

Bone Remodeling

  • Role of Osteoblasts and Osteoclasts: 5% to 10% of skeleton remodeled yearly.

  • Balance: Bone is deposited and broken down in response to stresses.

Types of Fractures

  • Classification: Displaced vs. non-displaced, complete vs. incomplete, open vs. closed.

  • Common Fracture Types: Comminuted, compression, spiral, epiphyseal, depressed, greenstick.

Bone Healing Process

  • Stages of Healing: Hematoma formation, fibrocartilaginous callus formation, bony callus formation, bone remodeling.

Bone Disorders

  • Osteomalacia/Rickets: Poorly mineralized bones.

  • Osteoporosis: Bone resorption exceeds formation, leading to weak bones, common in aging, especially postmenopausal women.

  • Paget's Disease: Excessive and disorganized bone remodeling.

Abnormal Spinal Curvatures

  • Scoliosis: Side-to-side curvature affecting respiratory function.

  • Kyphosis: Forward hunching, may lead to respiratory issues.

  • Lordosis: Exaggerated lower back curve, potential discomfort.

Summary

  • Bone Development Timeline: Starts as hyaline cartilage, transitions to bony structures, growth plates close by the early 20s, with early growth patterns differing by sex.

  • Nutrition and Hormones: Nutritional components like calcium and vitamin D are vital for bone health; hormones influence growth and remodeling significantly.