Skeletal System Overview

Overview

This lecture covers the human skeletal system, including its functions, structure, bone types, internal anatomy, bone cells, bone remodeling, fracture types, and the healing process.

Skeletal System Functions

• Supports the body and protects internal organs.
• Acts as a reservoir for essential minerals (e.g., calcium).
• Produces red and white blood cells in bone marrow.
• Enables movement in coordination with muscles.
• Skeletal and muscular systems work together (musculoskeletal system).

Structure of the Skeletal System

• Adults have 206 bones; babies have more that fuse with age.
• Divided into axial skeleton (skull, ear bones, hyoid, vertebral column, rib cage) and appendicular skeleton (arms, shoulder girdle, legs, pelvic girdle).
• Axial skeleton supports head/neck and aids breathing; appendicular skeleton enables limb movement.

Classification of Bones

• Long bones: cylindrical, longer than wide (e.g., femur, tibia, humerus, phalanges).
• Short bones: cube-like, equal length and width (e.g., carpals, tarsals).
• Sesamoid bones: small, round, within tendons (e.g., patella).
• Flat bones: thin, usually curved (e.g., cranial bones, scapula).
• Irregular bones: complex shapes (e.g., vertebrae).

Internal Bone Structure

• Compact bone: hard outer layer for protection.
• Spongy (cancellous) bone: internal lattice containing marrow.
• Red marrow: produces blood cells (hematopoiesis).
• Yellow marrow: stores fat for energy.

Bone Cells and Bone Remodeling

• Osteoblasts: build new bone.
• Osteocytes: maintain bone tissue.
• Osteoclasts: break down bone tissue for remodeling and calcium release.
• Bone remodeling: cycle of resting, resorption (breakdown), reversal, formation, and mineralization.
• Bone remodeling maintains strength and regulates calcium.

Cartilage and Bone Development

• Chondroblasts: produce cartilage; mature into chondrocytes.
• Cartilage supports joints and serves as a template for bone development in fetuses.

Bone Fractures and Healing

• Hematoma forms at fracture site due to blood vessel rupture.
• Chondrocytes and osteoblasts form internal (cartilage) and external (cartilage and bone) calluses to stabilize fracture.
• Osteoclasts remove damaged bone; osteoblasts rebuild bone during healing.

Types of Fractures

• Closed (simple): bone breaks but does not pierce skin.
• Open (compound): bone breaks through skin, increasing infection risk.
• Comminuted: bone shatters into three or more pieces.
• Impacted (buckle): bone ends are driven into each other (common in children).
• Greenstick: bone bends and partially cracks (common in children).

Key Terms & Definitions

• Axial skeleton — central skeleton (skull, vertebrae, ribs).
• Appendicular skeleton — limbs and girdles (arms, legs, shoulder, pelvis).
• Osteoblast — bone-forming cell.
• Osteocyte — mature bone cell that maintains tissue.
• Osteoclast — bone-resorbing cell.
• Hematopoiesis — blood cell production in marrow.
• Chondroblast — cartilage-forming cell.
• Callus — tissue that stabilizes a fracture during healing.

Action Items / Next Steps

• Review fracture types for exam.
• Study bone remodeling cycle phases.
• Complete any assigned readings on skeletal system anatomy and physiology.