Study Guide: The Skeletal System (Anatomy & Physiology)

Unit 11 – The Skeletal System

Overview of the Skeletal System

The skeletal system provides the structural framework for the human body, supports movement, protects internal organs, stores minerals, and produces blood cells. Understanding its structure and function is fundamental in anatomy and physiology.

• Functions: Support, protection, movement, mineral storage (especially calcium and phosphorus), blood cell production (hematopoiesis), and energy storage (yellow marrow).

Gross Anatomy of Bone

Bones have distinct anatomical features that contribute to their function and classification.

• Compact bone: Dense outer layer providing strength.

• Spongy bone: Porous inner layer containing red marrow.

• Articular cartilage: Covers joint surfaces, reducing friction.

• Periosteum: Outer fibrous membrane covering bone.

• Endosteum: Membrane lining the medullary cavity.

• Medullary cavity: Central cavity containing marrow.

• Yellow marrow: Stores fat.

• Red marrow: Site of blood cell formation.

• Epiphysis: Ends of long bones.

• Diaphysis: Shaft of long bones.

• Epiphyseal plate: Growth plate in children.

• Nutrient foramen: Opening for blood vessels.

• Perforating fibers (Sharpey's fibers): Secure periosteum to bone.

Bone Matrix Composition

The bone matrix consists of organic and inorganic components, each contributing to bone's properties.

• Organic matrix: Mainly collagen fibers, providing flexibility and tensile strength.

• Inorganic matrix: Primarily hydroxyapatite (calcium phosphate crystals), providing hardness and resistance to compression.

Cells of Bone Tissue

Bone tissue contains several specialized cell types, each with unique functions.

• Osteon (Haversian system): Structural unit of compact bone.

• Haversian (central) canal: Contains blood vessels and nerves.

• Osteocytes: Mature bone cells maintaining bone tissue.

• Osteoblasts: Bone-forming cells.

• Osteoclasts: Bone-resorbing cells.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny canals connecting lacunae.

• Lamellae: Concentric rings of bone matrix.

• Trabeculae: Lattice-like network in spongy bone.

• Bone lining cells: Flat cells on bone surfaces.

• Perforating (Volkmann's) canal: Channels for blood vessels perpendicular to Haversian canals.

• Interstitial, circumferential, concentric lamellae: Types of lamellae based on location.

• Collagen fibers: Provide tensile strength.

Bone Markings

Bones display various markings that serve as attachment points or passageways for nerves and blood vessels.

• Processes: Projections for muscle/ligament attachment (e.g., spine, condyle, tubercle, tuberosity, trochanter, crest, line).

• Depressions/openings: Allow passage of vessels/nerves (e.g., fossa, facet, fissure, foramen, meatus, canal, sinus, sulcus, ramus, notch).

Classification of Bones by Shape

Bones are classified based on their shape and structure.

• Long bones: Longer than wide (e.g., femur, humerus).

• Short bones: Cube-shaped (e.g., carpals, tarsals).

• Flat bones: Thin, flattened (e.g., sternum, skull bones).

• Irregular bones: Complex shapes (e.g., vertebrae, hip bones).

• Sesamoid bones: Embedded in tendons (e.g., patella).

Bone Formation (Ossification)

Bone develops through two main processes: endochondral and intramembranous ossification.

• Endochondral ossification: Bone forms by replacing hyaline cartilage (most bones).

• Intramembranous ossification: Bone develops from fibrous membranes (e.g., flat bones of skull).

Bone Growth

Bones grow in length and thickness through specific mechanisms.

• Epiphyseal plate (growth plate): Site of longitudinal growth in children and adolescents.

• Appositional growth: Increase in bone thickness.

• Hormonal regulation: Growth hormone, estrogen, and testosterone regulate bone growth. These hormones are produced by the pituitary gland (growth hormone) and gonads (estrogen, testosterone).

Bone Remodeling

Bone is continuously renewed through remodeling, balancing resorption and formation.

• Remodeling: Ongoing replacement of old bone by new bone tissue.

• Regulation: Controlled by hormones such as parathyroid hormone (PTH) and calcitonin.

• Stress and exercise: Mechanical stress stimulates bone formation.

• Glands: Parathyroid glands (PTH), thyroid gland (calcitonin).

Compact vs. Spongy Bone

Bone tissue is organized into two main types, each with distinct structure and function.

• Compact bone: Dense, forms outer layer, provides strength.

• Spongy bone: Porous, contains trabeculae, houses red marrow.

Nutritional Factors for Bone Health

Proper nutrition is essential for maintaining healthy bones.

• Key nutrients: Calcium, phosphorus, vitamin D, vitamin C, protein.

• Role: Support bone mineralization and collagen synthesis.

Classification of Joints

Joints are classified by structure and function, allowing varying degrees of movement.

• Structural classification: Fibrous, cartilaginous, synovial, bony.

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

Synovial Joints

Synovial joints are the most movable type of joint, characterized by a synovial cavity.

• Components: Joint capsule, synovial membrane and fluid, articular cartilage, fat pad, meniscus, ligament, tendon, bursa.

Axial and Appendicular Skeleton

The human skeleton is divided into two main parts.

• Axial skeleton: Skull, vertebral column, ribs, sternum.

• Appendicular skeleton: Limbs and girdles (shoulder and pelvic).

• Number of bones: 206 in the adult human skeleton.

Types of Diarthrotic (Synovial) Joints

There are six main types of synovial joints, each allowing specific movements.

Type	Example
Gliding (plane)	Intercarpal joints
Hinge	Elbow, knee
Ball and socket	Shoulder, hip
Saddle	Thumb (carpometacarpal joint)
Ellipsoid (condyloid)	Wrist
Pivot	Atlas/axis (neck)

Articulations and Sinuses

Bones articulate (form joints) with other bones, and some bones contain sinuses.

• Articulations: Points where bones meet.

• Sinuses: Air-filled cavities in bones (e.g., ethmoid, frontal, sphenoid, maxillary).

Movements at Synovial Joints

Synovial joints allow a variety of movements.

Movement	Description
Flexion	Decreases angle between bones
Extension	Increases angle between bones
Hyperextension	Extension beyond anatomical position
Dorsiflexion	Upward movement of foot
Plantar flexion	Downward movement of foot
Abduction	Movement away from midline
Adduction	Movement toward midline
Opposition	Thumb movement to touch fingers
Rotation	Bone turns around its own axis
Retraction	Moving a part backward
Circumduction	Circular movement
Supination	Turning palm upward
Pronation	Turning palm downward
Inversion	Turning sole of foot inward
Eversion	Turning sole of foot outward

Bone Fracture Repair

Bone repair is a multi-step process restoring bone integrity after injury.

• Steps: Hematoma formation, fibrocartilaginous callus formation, bony callus formation, bone remodeling.

Additional info: This study guide is based on a list of learning objectives and key terms for a college-level Anatomy & Physiology course, focusing on the skeletal system. It is suitable for exam preparation and review.