SKELETAL

Skeletal System

The body’s framework made of bones, cartilage, tendons, and ligaments. Bones grow, feel pain, adapt to stress, and repair after injury.

Cartilage

Rubbery tissue at the ends of bones for smooth movement; also found in the nose, ears, chest, and windpipe.

Tendons

Strong cords that attach muscles to bones.

Ligaments

Stretchy bands that connect bones to other bones and prevent excessive movement.

Functions of the Skeletal System

Support, protection, movement, mineral storage, and blood cell production.

Body Support (Function)

Bones hold body weight; cartilage provides flexible support; ligaments hold bones together.

Organ Protection (Function)

Bones shield organs — skull protects brain, vertebrae protect spinal cord, rib cage protects heart and lungs.

Body Movement (Function)

Muscles pull on bones via tendons; joints allow movement; ligaments prevent excessive bending.

Mineral Storage (Function)

Bones store calcium and phosphorus; release them into blood if levels drop; store fat for energy.

Blood Cell Production (Function)

Red bone marrow inside bones makes blood cells and platelets.

Bone Histology

Study of bone structure; cells produce a matrix containing collagen and proteoglycans.

Collagen

Fibrous protein giving flexibility and strength; resists pulling and compression; important in tendons, ligaments, and cartilage.

Proteoglycans

Water-trapping proteins that make cartilage smooth and resilient.

35% organic

(collagen, proteoglycans) for flexibility

65% inorganic

(hydroxyapatite) for hardness

Hydroxyapatite

Calcium phosphate crystal (Ca₁₀(PO₄)₆(OH)₂) that makes bones hard and strong.

Brittle Bone Disease

another word for Osteogenesis Imperfecta

Osteoclasts

Bone-destroying cells that break down bone (bone resorption) to release calcium and phosphate into blood; large and multinucleated; from red marrow cells.