Skeletal System: Structure, Function, and Physiology Study Guide

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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 rigid framework that supports the body and cradles soft organs.
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: Yellow bone marrow stores lipids as an energy reserve.

Section 6-2: Bone Classification and Bone Markings

Bone Shapes and Examples

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

Long Bones: Longer than they are wide (e.g., femur, humerus).
Short Bones: Approximately equal in length and width (e.g., carpals, tarsals).
Flat Bones: Thin and broad (e.g., sternum, skull bones).
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 bone 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: Rough projection.
Tubercle: Small, rounded projection.
Crest: Prominent ridge.
Line: Low ridge.
Spine: Pointed process.

Long Bone Structure

Epiphysis: The ends of a long bone.
Diaphysis: The shaft of a long bone.
Metaphysis: The region where the diaphysis and epiphysis meet.

Structural Differences: Compact bone is dense and forms the outer layer, while spongy bone is lighter and found at the ends of long 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).
Inorganic: Calcium phosphate and calcium hydroxide form hydroxyapatite crystals (provide strength).

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 provide flexibility.
Hydroxyapatite crystals provide compressive strength.

Section 6-4: Compact and Spongy Bone Structure

Compact Bone

Osteon: Structural unit of compact bone.
Central Canal: Contains blood vessels and nerves.
Lamellae: Concentric rings of bone matrix.
Lacunae: Small spaces housing osteocytes.
Canaliculi: Tiny channels connecting lacunae.
Perforating (Volkmann's) Canals: Connect central canals across osteons.

Spongy Bone

Trabeculae: Network of bony struts.
Red Bone Marrow: Site of hematopoiesis.
Yellow Bone Marrow: Stores fat.

Section 6-5: Bone Formation and Growth

Ossification Processes

Intramembranous Ossification: Bone develops from a fibrous membrane (e.g., flat bones of the skull).
Endochondral Ossification: Bone forms by replacing hyaline cartilage (e.g., long bones).

Growth Plates and Bone Growth

Epiphyseal Plate: Region of growing cartilage in long bones.
Appositional Growth: Increase in bone diameter.
Interstitial Growth: Increase in bone length.

X-ray Use: Epiphyseal lines indicate growth completion; presence of plate suggests ongoing growth.

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 and C) is essential.
Hormones: Growth hormone, thyroid hormone, sex hormones, and calcitonin regulate bone growth and maintenance.

Section 6-8: Calcium Homeostasis and Bone Physiology

Calcium Reservoir

Bones act as a major calcium reservoir, critical 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.

Rickets: Vitamin D deficiency leads to soft, weak bones in children.

Section 6-9: Bone Fractures and Repair

Types of Fractures

Simple (Closed) Fracture: Bone breaks but does not penetrate skin.
Compound (Open) Fracture: Bone breaks and penetrates skin.
Comminuted Fracture: Bone shatters into multiple pieces.
Greenstick Fracture: Incomplete break, common in children.

Steps of Fracture Repair

Hematoma formation
Fibrocartilaginous callus formation
Bony callus formation
Bone remodeling

Section 6-10: Bone Aging and Disorders

Osteopenia and Osteoporosis

Osteopenia: Reduced bone mass due to aging.
Osteoporosis: Severe loss of bone density, increasing fracture risk.

Summary Table: Bone Markings

Bone Marking	Description	Example
Foramen	Round opening for nerves/vessels	Foramen magnum (skull)
Fossa	Shallow depression	Olecranon fossa (humerus)
Process	Projection/bump	Mastoid process (skull)
Condyle	Rounded articular area	Femoral condyle
Crest	Prominent ridge	Iliac crest (pelvis)
Head	Expanded end	Head of femur

Key Equations

Hydroxyapatite formation:
Bone remodeling rate:

Additional info: Some details, such as the full list of bone markings and the summary table, were inferred and expanded for completeness and clarity.