1. General Functions of Bone & the Skeletal System

Overview of Skeletal System Functions

• Support: The skeleton provides a structural framework for the body, supporting soft tissues and providing attachment points for muscles.

• Protection: Bones protect vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Movement: Bones act as levers that muscles pull on to produce movement.

• Mineral Storage: Bones store minerals, especially calcium and phosphorus, which can be released into the bloodstream as needed.

• Blood Cell Production: Hematopoiesis occurs in the red bone marrow, producing red and white blood cells and platelets.

• Triglyceride Storage: Yellow bone marrow stores fat as an energy reserve.

2. Structural Components – Microscopic Anatomy

Cellular and Extracellular Components of Bone Tissue

• Osteoblasts: Bone-forming cells that secrete bone matrix.

• Osteocytes: Mature bone cells that maintain bone tissue.

• Osteoclasts: Large cells that resorb or break down bone matrix.

• Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.

• Extracellular Matrix (ECM): Composed of organic components (collagen fibers) and inorganic components (hydroxyapatite crystals).

Functions of Components: Osteoblasts build bone, osteoclasts break it down, and osteocytes maintain the matrix.

Structural Organization of Compact Bone

• Osteon (Haversian System): The basic structural unit of compact bone, consisting of concentric lamellae around a central canal.

• Central Canal: Contains blood vessels and nerves.

• Perforating (Volkmann's) Canals: Connect central canals of adjacent osteons.

• Lacunae: Small spaces containing osteocytes.

• Canaliculi: Tiny channels connecting lacunae, allowing for nutrient and waste exchange.

Types of Cartilage in the Skeletal System

• Hyaline Cartilage: Most abundant; provides support and flexibility (e.g., articular cartilage, costal cartilage).

• Elastic Cartilage: Contains elastic fibers; found in the ear and epiglottis.

• Fibrocartilage: Highly compressible; found in intervertebral discs and menisci.

Function of Cartilage: Reduces friction, absorbs shock, and provides flexible support.

3. Structural Components – Gross Anatomy

Gross Anatomy of a Long Bone

• Diaphysis: The shaft of a long bone, composed mainly of compact bone.

• Epiphyses: The ends of a long bone, consisting mostly of spongy bone covered by compact bone.

• Metaphysis: The region between diaphysis and epiphysis; contains the epiphyseal plate (growth plate) in growing bones.

• Medullary Cavity: Central cavity containing yellow bone marrow in adults.

• Periosteum: Dense connective tissue covering the outer surface of bone.

• Endosteum: Thin membrane lining the medullary cavity.

Other Features: Articular cartilage covers joint surfaces; nutrient arteries supply blood.

4. Physiology of Embryonic Bone Formation (Ossification, Osteogenesis)

Bone Formation Processes

• Intramembranous Ossification: Bone develops directly from mesenchymal tissue (e.g., flat bones of the skull).

• Endochondral Ossification: Bone forms by replacing hyaline cartilage (e.g., long bones).

Osteogenic Cells: Stem cells that give rise to osteoblasts.

Comparison: Primary vs. Secondary Bone

• Primary (Woven) Bone: First bone formed; irregular arrangement of collagen fibers; later replaced by secondary bone.

• Secondary (Lamellar) Bone: Mature bone with organized lamellae; stronger and more resilient.

5. Physiology of Bone Growth, Repair, and Remodeling

Bone Growth

• Longitudinal Growth: Occurs at the epiphyseal plate; responsible for increase in length.

• Appositional Growth: Increase in bone thickness.

Bone Remodeling and Repair

• Remodeling: Continuous process of bone resorption and formation; maintains bone strength and mineral homeostasis.

• Repair: Involves hematoma formation, fibrocartilaginous callus formation, bony callus formation, and bone remodeling.

Hormonal Regulation of Skeletal Growth

• Growth Hormone: Stimulates bone growth at the epiphyseal plate.

• Thyroid Hormone: Modulates activity of growth hormone.

• Sex Hormones: Promote growth spurts and closure of epiphyseal plates.

• Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclasts.

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

• Vitamin D: Promotes calcium absorption in the gut.

6. Organization of the Skeletal System

Axial and Appendicular Skeleton

• Axial Skeleton: Consists of the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Includes the pectoral girdle, pelvic girdle, and limbs.

7. Gross Anatomy of Bones of the Axial Skeleton

Major Bones and Their Features

• Skull: Frontal, parietal, temporal, occipital, sphenoid, ethmoid, maxilla, zygomatic, mandible.

• Vertebral Column: Cervical (7), thoracic (12), lumbar (5), sacrum, coccyx.

• Thoracic Cage: Sternum, ribs.

Vertebral Column Regions: Cervical, thoracic, lumbar, sacral, coccygeal.

8. Anatomical Classification of Joints

Structural and Functional Classification

• Fibrous Joints: Bones joined by dense connective tissue; little or no movement (e.g., sutures of the skull).

• Cartilaginous Joints: Bones joined by cartilage; limited movement (e.g., intervertebral discs).

• Synovial Joints: Bones separated by a fluid-filled cavity; freely movable (e.g., knee, shoulder).

Functional Classification: Synarthroses (immovable), amphiarthroses (slightly movable), diarthroses (freely movable).

9. Synovial Joints

Structural Components of Synovial Joints

• Articular Cartilage: Covers bone surfaces at the joint.

• Joint (Synovial) Cavity: Space filled with synovial fluid.

• Articular Capsule: Encloses the joint cavity; composed of fibrous and synovial layers.

• Synovial Fluid: Lubricates and nourishes the joint.

• Accessory Structures: Bursae (fluid-filled sacs), tendon sheaths, ligaments.

Types of Synovial Joints and Movements

• Plane (Gliding) Joints: Allow sliding movements (e.g., intercarpal joints).

• Hinge Joints: Permit flexion and extension (e.g., elbow, knee).

• Pivot Joints: Allow rotation (e.g., atlantoaxial joint).

• Condyloid Joints: Permit movement in two planes (e.g., wrist).

• Saddle Joints: Allow movement in two planes (e.g., thumb).

• Ball-and-Socket Joints: Allow movement in multiple axes (e.g., shoulder, hip).

Movements: Flexion, extension, abduction, adduction, rotation, circumduction.

Table: Comparison of Primary and Secondary Bone

Key Equations

• Calcium Homeostasis:

Additional info:

• Some details, such as the specific names of bones and the steps of bone repair, were expanded for completeness.

• Table content and equations were inferred and added for academic clarity.