Lecture 2: Skeletal System Flashcards
Rigid materials
- Resist stress without much deformation
- e.g. bone, keratin, dentin, enamel
Tensile materials
Resist being pulled on
E.g. silk, collagen
Pliant materials
Must deform in order to function properly
E.g. cartilage, mucus, synovial fluid
Stress
- Force applied per unit area
- measured in pascals
Tensile stress
Tension, pulling
Compressive stress
Compression, pushing
Strain
Deformation caused by applied stress
Change in length divided by original length
Dimensionless
Stress-strain curve
The slope of the curve is a measure of stiffness
Elastic region
- up to yield point
- item will return to original length
Plastic region
- past yield point
- item changes shape permanently
Elastic material
Linear relationship between stress and strain
Viscoelastic material
Nonlinear relationship between stress and strain
Safety factor
Strength / typical load
E.g. failure stress / typical stress
Energy
Energy stored/put in when a stress is applied is proportional to area under the curve
Energy can be recovered when stress is relieved (only a portion recovered in viscoelastic material)
Functions of the skeleton
Leverage/movement Support Protection Storage Blood cell formation
Bone cells
Osteocytes: transport metabolites, sense mechanical stress, communication
Osteoblasts: deposition
Osteoclasts: resorption
Cortical bone tissue
Compact, very dense
Outer layer
Stiff and strong
Cancellous/trabecular bone tissue
- Spongy, very porous
- Inner layer
- Trabeculae adapt to direction of loading and add strength
- High energy absorption, not as strong as cortical tissue
Bone tissue composition
25-30% water weight
60-70% minerals/collagen
Bone minerals
Provide compressive strength and rigidity (calcium and phosphate)
Bone collagen
Provides tensile strength & flexibility (protein)
Ossification
Formation of bone by activity of osteoblasts and osteoclasts
Wolff’s Law
Bone grows or remodels in response to forces or stresses upon it
Appositional growth
Growth in diameter is controlled by the amount of mechanical stress and gravity placed on bone
Deposition
Osteoblasts
Response to increased stress (weight-bearing exercise)
Resorption
Osteoclasts
Response to decreased stress (disuse, immobilization, microgravity)
Osteoporosis
Resorption exceeds deposition of bone
too many holes, increased risk of fracture
Bones and physical activity
- Bones require mechanical stress to grow and strengthen
- loading -> deposition -> increased density
Anisotropic property of bone
Response depends on the direction of load application
Viscoelastic properties of bone
Response depends on rate and duration of loading
Loads applied to bone
Compression, tension, shear, bending
Cartilage
- Firm, flexible tissue
- no blood supply or nerves
- nourished by fluid within joint
- reduces contact stress
Articular/hyaline cartilage
- covers joint ends at articulation
- 60-80% water
- contains collagen and proteoglycan
Fibrocartilage
- found where articular cartilage meets tendon/ligament
- improves fit between bones
- serves as intermediary between hyaline cartilage and other connective tissues
Ligaments
Fibrous CT, connects bone to bone
- consists of collagen, elastic, and reticulin
- viscoelastic
Types of synovial joints
Hinge: interphalangeal Pivot: radioulnar Condylar: knee Ellipsoid: metacarpophalangeal Saddle: intercarpal Ball and socket: shoulder
