Skeletal System: Structure, Function, and Organization Study Notes

Skeletal System

Bone Structure & Function

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

• Support: Bones provide structural support for the entire body, maintaining its shape.

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

• Movement: Bones act as levers for muscles, enabling movement.

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

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

Bone Tissue Types

Bones are composed of two main types of tissue, each with distinct characteristics and functions.

• Compact Bone: Dense and strong, forms the outer layer of bones and provides strength for weight-bearing.

• Spongy (Cancellous) Bone: Porous and lightweight, found at the ends of long bones and inside flat bones; contains red bone marrow.

Organization of the Skeletal System

The skeletal system is divided into two major divisions, each with specific components and functions.

Division	What it includes	Primary Function
Axial Skeleton	Skull, vertebral column, rib cage	Protection of vital organs, support
Appendicular Skeleton	Limbs, girdles (shoulder and pelvic)	Movement, manipulation of environment

Total Bones

The adult human skeleton contains approximately 206 bones.

Axial Skeleton Labeling

The axial skeleton includes the following structures:

• Skull

• Cranial bones

• Facial bones

• Hyoid bone

• Vertebral column

• Thoracic cage (ribs and sternum)

• Sacrum

• Coccyx

Main function: Protection and support.

Appendicular Skeleton Labeling

The appendicular skeleton consists of the bones of the limbs and girdles:

• Upper Limb & Girdle: Clavicle, scapula, humerus, radius, ulna, carpals, metacarpals, phalanges

• Lower Limb & Girdle: Coxal (hip) bone, femur, patella, tibia, fibula, tarsals, metatarsals, phalanges

Bone Classification Based on Shape

Bones are classified by their shapes, which relate to their functions.

Bone Shape	Description	Example
Long	Longer than wide, shaft with two ends	Femur, humerus
Short	Cube-shaped, mostly spongy bone	Carpals, tarsals
Flat	Thin, flattened, usually curved	Sternum, skull bones
Irregular	Complex shapes	Vertebrae, hip bones
Sesamoid	Embedded in tendons	Patella

Anatomy of a Long Bone

Long bones have distinct anatomical regions:

• Diaphysis: Shaft of the bone

• Epiphysis: Ends of the bone

• Articular cartilage: Covers joint surfaces

• Periosteum: Outer membrane

• Medullary cavity: Central cavity containing marrow

• Endosteum: Membrane lining the medullary cavity

Epiphyseal plate: Region of bone growth in children; becomes the epiphyseal line in adults.

Joints

Joints, or articulations, are sites where two or more bones meet, allowing for movement and flexibility.

Types of Joints by Structure

Joint Type	Description	Example
Fibrous	Connected by dense connective tissue	Sutures in skull
Cartilaginous	Connected by cartilage	Intervertebral discs
Synovial	Freely movable, joint cavity with synovial fluid	Knee, shoulder

Types of Synovial Joints

• Hinge: Elbow

• Ball-and-socket: Shoulder, hip

• Pivot: Atlas and axis (neck)

• Gliding: Carpals

• Condyloid: Wrist

• Saddle: Thumb

Bone Remodeling Process

Bone remodeling is a continuous process involving bone resorption and formation, essential for bone health and repair.

Key Cells

• Osteoclasts: Break down bone tissue

• Osteoblasts: Build new bone tissue

• Osteocytes: Maintain bone tissue

Importance of Bone Remodeling

• Repairs micro-damage

• Adapts bone strength to stress

• Prevents bone brittleness

Spine (Vertebral Column) Labeling

The vertebral column is divided into regions:

• Cervical vertebrae: 7

• Thoracic vertebrae: 12

• Lumbar vertebrae: 5

• Sacral vertebrae: 5 (fused)

• Coccygeal vertebrae: 4 (fused)

Fracture Healing Process

Bone healing after a fracture occurs in several stages:

1. Hematoma formation: Blood clot forms at the fracture site

2. Fibrocartilaginous callus formation: Soft callus bridges the gap

3. Bony callus formation: Hard callus replaces the soft callus

4. Bone remodeling: Bone is reshaped to its original form

Clinical Application: Proper immobilization is crucial for effective fracture healing.

Study Tip

Use color coding for diagrams and create flashcards for bone names and joint types to enhance memorization.

Additional info: Some content was expanded for clarity and completeness, including definitions, examples, and explanations of processes.