Chapter 3 The Skeletal-Articular System

1. Chapter 3The Skeletal-Articular System Ronald F. Zernicke, Gregory R. Wohl, and Jeremy M. LaMothe

2. Skeletal-Articular Physiology • Overview • Low cellularity • Extracellular matrix (EM) constitutes majority of volume • EM of soft connective tissues is 70-75% water • Collagen comprises 60-70% of dry mass • Muscle microfibrils form subfibrils, which form fiber bundles • Muscle fiber bundles are collated into fascicles

3. Skeletal-Articular Physiology (cont’d) • Ligaments • Tether bones across a joint • Control relative motion of joint • Tendons • Connect muscles to bones • Transmit muscular forces to bones

4. Skeletal-Articular Physiology (cont’d) • Menisci • Maintain joint components in appropriate position • Reduce joint stress by bearing load • Enhance rotation in synovial joints • Bones • Mechanical support • Center for hematopoiesis • Largest calcium reservoir

5. Frontal Section of Knee

6. Fiber Pattern of Meniscus

7. Structural Hierarchy of Tendon Organization

8. Skeletal-Articular Tissue Turnover • Fine balance of extracellular matrix components • Turnover of damaged matrix • Repairing or building new matrix after injury or mechanical stimuli • Fibroblasts: primary cells in ligaments & tendons • Fibrochondrocytes: primary cells of menisci

9. Skeletal-Articular Tissue Turnover (cont’d) • Characteristics of fibrous connective tissue: • Limited vascularity • Restricted metabolic capacity of cells during matrix turnover • Less vigorous adaptive response to stimuli than in bone • Poor response to injury • Optimized for mechanical function

10. Skeletal-Articular Tissue Turnover (cont’d) • Characteristics of bone: • Most dynamic of skeletal-articular tissues • Can completely turnover in as little as 3 years • Types of cells: • Osteoblasts • Osteocytes • Osteoclasts • Modeling • Remodeling

11. Bone Modeling and Remodeling

12. Factors in Tissue Adaptation • Bone mineral density • Genetics (80%) • Environmental conditions • Bone strength • Bone mass • Bone density • Bone size • Bone geometry

13. Tissue Response to Mechanical Stimuli • Ligament & Tendon • Catabolic stimuli • Anabolic stimuli • Meniscus • Catabolic stimuli • Anabolic stimuli

14. Tissue Response to Mechanical Stimuli (cont’d) • Bone • Positive effects of exercise • Increase in bone cross-sectional area • Reduction in bone mechanical stresses • Increase in BMD • Increase in bone strength • Increased resistance to bending or torsion • Increased intestinal & renal calcium absorption & secretion

15. Relation Between Exercise and Bone Mass

16. Tissue Response to Mechanical Stimuli (cont’d) • Bone • Negative effects of very strenuous exercise • Microdamage from prolonged bouts of extremely intense exercise • Stress reactions • Stress fractures • Female athlete triad • Interruption of normal growth with extremely strenuous exercise

17. Tissue Response to Mechanical Stimuli (cont’d) • Interactions With Exercise • Genetics • Diet • Minerals (calcium) • Vitamin D • Protein • Fat • Hormones: growth hormone & estrogen • Development & aging

18. Mechanisms of Bone Adaptation • Proposed Strain Components • Magnitude • Frequency • Rate • Gradient

19. Strain Threshold Required for Osteogenesis

20. Mechanisms of Bone Adaptation (cont’d) • Mechanical Transduction • Cell populations (signal pathways) • Transduction mechanisms • Bone cell strain/stretch receptors, cytoskeleton • Piezoelectricity • Fluid flow • Shear flow • Ion flow • Nutrient flow

21. Section of Bone in Bending