Study Guide: The Skeletal System – Part 1

The Skeletal System

General Functions and Structures

The skeletal system provides the framework for the human body, supporting and protecting organs, enabling movement, and serving as a reservoir for minerals.

• Support: Bones form the body’s structural framework.

• Protection: Vital organs (e.g., brain, heart, lungs) are shielded by bones.

• Movement: Bones act as levers for muscles to produce movement.

• Mineral Storage: Bones store calcium and phosphorus.

• Blood Cell Production: Hematopoiesis occurs in red bone marrow.

Number of Bones: The average adult human skeleton contains 206 bones. Infants have more bones (about 270), which fuse during development.

Physiological Aspects of the Skeletal System

• Support and Protection: The skeleton supports body weight and protects internal organs.

• Movement: Bones interact with muscles to facilitate movement.

• Homeostasis: Bones help regulate mineral balance and blood cell production.

Bone Anatomy

Long Bone Anatomy

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

• Epiphyses: The ends of long bones, containing spongy bone and red marrow.

• Metaphysis: The region between diaphysis and epiphysis, including the growth plate.

• Medullary Cavity: Central cavity containing yellow marrow (fat storage).

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

Compact Bone (Diagram and Physiology)

• Structure: Dense, solid bone tissue forming the outer layer of bones.

• Osteons (Haversian systems): Cylindrical structures containing a central canal surrounded by concentric lamellae.

• Function: Provides strength and resistance to bending.

Spongy Bone (Diagram and Physiology)

• Structure: Porous, lattice-like bone tissue found at the ends of long bones and inside flat bones.

• Trabeculae: Thin columns of bone that form the framework of spongy bone.

• Function: Reduces bone weight and contains red marrow for hematopoiesis.

Bone Microanatomy Structures

• Lacunae: Small spaces housing osteocytes (bone cells).

• Lamellae: Layers of bone matrix within osteons.

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

Osteon Anatomy and Physiology

• Osteon: The functional unit of compact bone, consisting of a central canal, lamellae, lacunae, and canaliculi.

• Central (Haversian) Canal: Contains blood vessels and nerves.

Trabeculae (Relation to Spongy Bone)

• Definition: Interconnecting rods or plates of bone in spongy bone.

• Function: Provide structural support and house bone marrow.

Bone Growth and Development

Epiphysis and Diaphysis

• Epiphysis: End part of a long bone, involved in joint articulation and growth.

• Diaphysis: Shaft of the bone, providing length and support.

• Epiphyseal Plate (Growth Plate): Cartilaginous region where bone growth occurs in children and adolescents.

Osteoclasts and Osteoblasts

• Osteoblasts: Cells that build new bone matrix.

• Osteoclasts: Cells that break down bone matrix, aiding in bone remodeling.

• Bone Homeostasis: Balance between osteoblast and osteoclast activity maintains bone density.

Bone Remodeling and Repair

• Bone Remodeling: Continuous process of bone resorption and formation.

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

Purpose of Red Bone Marrow

• Function: Site of hematopoiesis (production of red and white blood cells and platelets).

• Location: Found in spongy bone of flat bones and epiphyses of long bones.

Bone Growth and Repair Processes

• Endochondral Ossification: Bone develops from hyaline cartilage (most bones).

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

Epiphyseal Plate/Cartilage

• Function: Allows for longitudinal bone growth during childhood and adolescence.

• Closure: Plate ossifies and becomes the epiphyseal line in adults.

Bone Health and Nutrition

Vitamins and Minerals

• Vitamin D: Essential for calcium absorption.

• Vitamin C: Required for collagen synthesis.

• Calcium: Most abundant mineral in bone; provides strength and rigidity.

• Phosphorus: Important for bone mineralization.

Minerals Needed by the Skeletal System

Mineral	Function
Calcium	Bone strength, muscle contraction, nerve function
Phosphorus	Bone mineralization, energy metabolism
Magnesium	Bone structure, enzyme activity
Fluoride	Bone and dental health

Fetal Bone Development

• Endochondral Ossification: Most bones form from cartilage templates.

• Intramembranous Ossification: Flat bones form from connective tissue membranes.

Exercise and Bone Health

• Effect: Weight-bearing exercise stimulates bone formation and increases bone density.

• Prevention: Reduces risk of osteoporosis and bone loss.

Bone Disorders and Hormonal Regulation

Rickets

• Definition: A disease in children caused by vitamin D deficiency, leading to soft, weak bones.

• Symptoms: Bone pain, deformities, delayed growth.

Regulation of Calcium Levels

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

• Calcitonin: Lowers blood calcium by inhibiting bone resorption.

• Vitamin D: Enhances calcium absorption from the gut.

Effect of Sex Hormones on Bone Growth

• Estrogen and Testosterone: Stimulate bone growth during puberty and maintain bone density.

• Bone Loss: Decreased hormone levels (e.g., menopause) can lead to increased bone resorption and osteoporosis.

Bone Loss Due to Hormonal Changes

• Osteoporosis: Condition characterized by decreased bone mass and increased fracture risk, often due to hormonal changes.

• Prevention: Adequate calcium, vitamin D, and regular exercise are important for bone health.

Identifying Parts of the Long Bone

• Key Parts: Diaphysis, epiphysis, metaphysis, medullary cavity, periosteum, endosteum, articular cartilage.

• Application: Understanding bone anatomy is essential for identifying fractures and diseases.

Additional info: This study guide covers foundational concepts in skeletal anatomy and physiology, suitable for exam preparation in a college-level Anatomy & Physiology course.