Overview
This lecture covers the structure, function, and anatomy of the skeletal system, the processes of bone modeling and remodeling, and bone health assessment.
Bone Structure and Function
- Bone is a composite material with collagen fibers for flexibility and a mineralized matrix (mainly calcium) for strength.
- Bones are living tissues, continuously breaking down and rebuilding to adapt to stress.
Importance of the Skeletal System
- The human skeleton has 206 bones and connective tissues: ligaments (bone to bone), tendons (bone to muscle), and cartilage (joint cushioning).
- The skeleton enables movement, provides structural support, protects organs (e.g., skull for brain, ribs for lungs/heart), and houses bone marrow for blood cell production.
- Bones store minerals like calcium, phosphorus, and magnesium.
Bone Anatomy and Structure
- The skeleton has two main parts: axial (skull, vertebral column, rib cage; 80 bones) and appendicular (limbs, shoulder, pelvis; 126 bones).
- Bone shapes: long (e.g., femur), short, flat (e.g., ribs), and irregular (e.g., wrist bones).
- Bone tissue consists of about 65% mineralized matrix (mostly hydroxyapatite) and 35% organic material (mainly collagen).
- Two main bone tissue types: trabecular (spongy, porous, at bone ends and vertebrae) and cortical (compact, dense, forms bone shafts).
Bone Tissues, Cells, and Remodeling
- Bones have various cell types: osteoprogenitor (immature), osteoblasts (build bone), osteoclasts (break down bone), and osteocytes (maintain bone).
- Bone modeling (growth/change in shape) occurs during childhood; remodeling (renewal at same site) continues in adulthood.
- About 10% of adult bone tissue remodels each year.
- Bone adapts to stress (Wolff’s law): weight-bearing exercises increase bone strength.
- Remodeling stages: osteocyte activation, osteoclast resorption, formation of cement line, osteoblast rebuilding, and mineralization.
- Vitamin C is needed for collagen synthesis in bone; deficiency can cause bone pain.
Bone Mineral Density (BMD)
- BMD measures the amount of calcified bone tissue (g/cm²); higher BMD means stronger bones.
- DEXA is the most common, accurate, and low-radiation method for measuring BMD.
- BMD measurement helps predict bone fracture risk; commonly measured at hip and spine.
Key Terms & Definitions
- Ligament — connective tissue attaching bone to bone.
- Tendon — connective tissue attaching muscle to bone.
- Cartilage — flexible connective tissue cushioning joints.
- Axial skeleton — central bones (skull, vertebral column, ribs).
- Appendicular skeleton — limb and girdle bones.
- Trabecular bone — spongy, porous bone tissue.
- Cortical bone — dense, compact bone tissue.
- Osteoblast — bone-building cell.
- Osteoclast — bone-resorbing cell.
- Osteocyte — mature bone cell involved in nutrient exchange.
- Bone remodeling — ongoing replacement of old bone tissue by new tissue.
- Bone Mineral Density (BMD) — measure of bone strength.
Action Items / Next Steps
- Review diagrams of axial and appendicular skeleton, trabecular vs. cortical bone.
- Make sure to complete web-based learning activities if using the online textbook version.