SKELETAL SYSTEM

Skeletal System

The skeletal system is the body system made up of bones, cartilage, ligaments, and joints.

An adult human has 206 bones.

This system provides structure, protection, movement, and performs important metabolic functions.

Support

The skeleton forms the structural framework of the body. It supports body weight and maintains posture, allowing the body to stand upright.

Protection

Bones protect vital organs:

• The skull protects the brain

• The vertebral column protects the spinal cord

• The rib cage protects the heart and lungs

Mineral Storage

Bones store minerals, mainly calcium and phosphorus.

These minerals can be released into the bloodstream when needed to maintain normal body functions.

Blood Cell Production (Hematopoiesis)

Blood cells are produced in red bone marrow. This includes:

• Red blood cells

• White blood cells

• Platelets

LONG BONES

Longer than they are wide; involved in movement

Examples: femur, humerus

SHORT BONES

cube-shaped; provide stability

Examples: carpals (wrist), tarsals (ankle)

FLAT BONES

thin and flat; protect organs

Examples: skull, ribs, sternum

IRREGULAR BONES

complex shapes

Examples: vertebrae, facial bones

COMPACT BONE

Dense, hard outer layer that provides strength and protection.

SPONGY BONE

Porous inner layer found mainly at the ends of long bones; contains red bone marrow.

RED BONE MARROW

produces blood cells

YELLOW BONE MARROW

stores fat and can convert to red marrow if needed

AXIAL SKELETON

Forms the central axis of the body and includes:

• Skull

• Vertebral column

• Rib cage

Primary function: support and protection

APPENDICULAR SKELETON

Includes:

• Upper limbs

• Lower limbs

• Shoulder girdle

• Pelvic girdle

Primary function: movement

JOINTS

A joint is the point where two bones meet.