Section 6-1: Major Functions of the Skeletal System

Overview of Skeletal System Functions

The skeletal system is essential for multiple physiological processes and structural support in the human body. It consists of bones, cartilage, and associated connective tissues.

• Support: Provides a framework for the body and supports soft tissues.

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

• Movement: Acts as levers for muscles to produce movement.

• Mineral Storage: Stores minerals such as calcium and phosphorus, which can be released into the bloodstream as needed.

• Blood Cell Production: Houses bone marrow, which produces red and white blood cells (hematopoiesis).

• Energy Storage: Stores lipids in yellow bone marrow.

Section 6-2: Bone Classification and Markings

Bone Shapes and Examples

Bones are classified by shape and structure, each serving specific functions.

• Long Bones: Longer than they are wide (e.g., femur, humerus).

• Short Bones: Nearly equal length and width (e.g., carpals, tarsals).

• Flat Bones: Thin and broad (e.g., sternum, skull).

• Irregular Bones: Complex shapes (e.g., vertebrae, pelvis).

• Sesamoid Bones: Small, round, and embedded in tendons (e.g., patella).

• Sutural Bones: Small bones located within sutures of cranial bones.

Bone Markings

Bones have various surface features called markings, which serve as attachment points for muscles, ligaments, and tendons, or as passageways for nerves and blood vessels.

• Process: Any projection or bump.

• Ramus: Extension of a bone making an angle with the rest of the structure.

• Foramen: Rounded passageway for blood vessels or nerves.

• Fossa: Shallow depression.

• Head: Expanded articular end of an epiphysis, separated from the shaft by a neck.

• Neck: Narrow connection between the epiphysis and diaphysis.

• Facet: Small, flat articular surface.

• Condyle: Smooth, rounded articular process.

• Trochanter: Large, rough projection (found only on femur).

• Tuberosity: Smaller, rough projection.

• Tubercle: Small, rounded projection.

• Crest: Prominent ridge.

• Line: Low ridge.

• Spine: Pointed process.

Long Bone Features

• Epiphysis: The ends of a long bone, usually wider than the shaft.

• Diaphysis: The shaft or central part of a long bone.

• Metaphysis: The region where the diaphysis and epiphysis meet.

Structural Differences: Compact bone is dense and forms the outer layer of bones, while spongy bone (cancellous bone) is lighter and found at the ends of long bones and inside flat bones.

Section 6-3: Bone Matrix and Cells

Bone Matrix Composition

The bone matrix is composed of organic and inorganic components, providing strength and flexibility.

• Organic: Collagen fibers (provide flexibility and tensile strength).

• Inorganic: Hydroxyapatite crystals (calcium phosphate and calcium hydroxide; provide hardness).

Osteogenic Cells: Stem cells that differentiate into osteoblasts. Osteoblasts: Cells that build new bone matrix. Osteocytes: Mature bone cells that maintain bone tissue. Osteoclasts: Cells that break down bone matrix.

Bone Flexibility and Strength

• Collagen fibers give bone flexibility.

• Hydroxyapatite crystals give bone strength and rigidity.

Section 6-4: Compact and Spongy Bone Structure

Compact Bone

• Osteon (Haversian system): Structural unit of compact bone; contains concentric lamellae around a central canal.

• Central Canal: Contains blood vessels and nerves.

• Canaliculi: Small channels connecting osteocytes.

• Perforating (Volkmann's) Canals: Connect central canals to each other and to the periosteum.

Spongy Bone

• Trabeculae: Network of struts and plates; spaces filled with bone marrow.

• Red Bone Marrow: Site of hematopoiesis.

• Yellow Bone Marrow: Stores fat.

Section 6-5: Bone Formation and Growth

Ossification Processes

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

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

Epiphyseal Line: Remnant of the epiphyseal plate, indicating where bone growth occurred.

Appositional Growth: Increase in bone diameter. Interstitial Growth: Increase in bone length.

Section 6-6: Bone Remodeling

Bone Remodeling

Bone remodeling is a continuous process of bone resorption and formation, balancing bone strength and mineral homeostasis.

• Osteoclasts: Resorb bone.

• Osteoblasts: Form new bone.

Remodeling is influenced by mechanical stress, hormones, and nutritional status.

Section 6-7: Exercise, Nutrition, and Hormones

Factors Affecting Bone Growth and Maintenance

• Exercise: Stimulates bone formation and increases bone density.

• Nutrition: Adequate intake of calcium, phosphate, and vitamins (especially D, C, and A) is essential.

• Hormones: Growth hormone, thyroid hormone, sex hormones, and calcitonin regulate bone growth and remodeling.

Section 6-8: Calcium Homeostasis and Hormonal Regulation

Calcium Reservoir

Bones act as a major reservoir for calcium, which is vital for muscle contraction, nerve function, and blood clotting.

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

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

• Vitamin D: Enhances calcium absorption from the gut.

Imbalances can lead to conditions such as rickets (vitamin D deficiency) and osteoporosis.

Section 6-9: Bone Fractures and Repair

Types of Fractures

• Simple (closed) fracture: Bone breaks but does not penetrate the skin.

• Compound (open) fracture: Bone breaks and penetrates the skin.

• Comminuted fracture: Bone is shattered into multiple pieces.

• Greenstick fracture: Bone bends and cracks, common in children.

Steps of Fracture Repair

1. Hematoma formation

2. Fibrocartilaginous callus formation

3. Bony callus formation

4. Bone remodeling

Section 6-10: Bone Aging and Disorders

Osteopenia and Osteoporosis

• Osteopenia: Reduced bone mass due to aging, less severe than osteoporosis.

• Osteoporosis: Severe loss of bone density, increasing fracture risk.

Prevention: Adequate calcium and vitamin D intake, regular weight-bearing exercise, and hormone regulation.

Table: Bone Markings and Their Functions

Key Equations

• Calcium Homeostasis:

• Bone Growth Rate:

Additional info: These notes expand on the provided study guide questions, offering definitions, examples, and context for each major topic in skeletal anatomy and physiology.