Overview
This lecture covers the structure, function, and types of bones in the human skeletal system, as well as key cells, bone growth, injury, and related disorders.
Skeletal System Overview
- The skeletal system includes bones and connective tissues: ligaments (bone to bone), tendons (muscle to bone), and cartilage.
- Bones are living tissues made of collagen (protein) and minerals.
- Functions include body support, organ protection, mineral storage, blood cell production, and enabling movement with muscles.
- Humans have an endoskeleton (internal skeleton) with about 206 bones in adulthood.
Bone Structure & Classification
- The skeleton is divided into axial (skull, vertebral column, ribcage) and appendicular (limbs, girdles) skeletons.
- Bone shapes:
- Long bones (femur, humerus), longer than wide, for movement.
- Short bones (carpals, tarsals), cube-shaped, for stability.
- Sesamoid bones (patella), round, handle pressure.
- Flat bones (skull, scapulae), thin and curved.
- Irregular bones (vertebrae), have unique shapes.
- Bone tissue types:
- Compact bone: hard outer layer.
- Spongy bone: inner layer with bone marrow.
Bone Marrow & Blood Formation
- Yellow marrow: stores fat for energy.
- Red marrow: produces red and white blood cells and platelets.
- Bones are vascular (rich in blood supply).
Bone Cells & Remodeling
- Osteoblasts produce bone tissue; mature into osteocytes which maintain structure.
- Osteoclasts break down bone using lysosomes for remodeling and mineral release.
- About 5-10% of the skeleton is remodeled each year.
- Calcium storage and release are hormonally regulated and are crucial for muscle contraction.
Cartilage and Bone Growth
- Chondroblasts create cartilage; chondrocytes maintain it.
- Cartilage forms the template for bone during fetal development.
- Bone growth occurs in length (via growth plates) and diameter.
Bone Injury & Disorders
- Bone fractures cause bleeding (fracture hematoma) and cell death near the break.
- Healing involves callus formation (internal: cartilage, external: cartilage and bone), osteoclasts remove damaged bone, and osteoblasts build new bone.
- Healing typically takes 6-8 weeks but varies.
- Fat embolism syndrome can occur if yellow marrow fat enters the bloodstream after a fracture.
- Osteogenesis imperfecta is a genetic disorder affecting collagen, making bones brittle.
Key Terms & Definitions
- Ligament — connective tissue linking bone to bone.
- Tendon — connective tissue connecting muscle to bone.
- Cartilage — flexible tissue at joints, precursor to bone.
- Osteoblast — cell that builds new bone tissue.
- Osteocyte — mature bone cell maintaining bone structure.
- Osteoclast — cell that breaks down bone tissue.
- Bone marrow — tissue inside bones producing blood cells.
- Chondroblast — cell that produces cartilage.
- Chondrocyte — mature cartilage cell.
- Fracture hematoma — blood collection at a bone break.
- Callus — tissue bridging and stabilizing a broken bone during healing.
Action Items / Next Steps
- Suggested reading: further explore bone growth zones and the role of the growth plate.