Exam 2 lectures

• Hyaline cartilage

  Translucent/glossy;  found in joints (articular), but also found in walls of the respiratory tract (larynx, trachea, nose, and bronchi), tips of the ribs; Provides nearly frictionless surface, disperses loads (dissipates to subchondral bone)

  cells dispersed throughout ground substance (imbibition of water provides rigidity)—fewer collagen fibers, so more translucent; large chondrocytes
• Fibrocartilage

  White/dense/opaque; more resilient/stronger than hyaline, found in TMJ, sternoclavicular joint disc, intervertebral discs, menisci (knee), labrum (hip and shoulder); Provides support against compressive forces (less matrix, more collagen than hyaline); densely layered collagen fibers; more flattened and organized cell rows

  chondrocytes packed in distinct layers between densely layered collagen—heavy collagen content, which makes it more white than hyaline cartilage
• Elastic Cartilage

  Yellow/glossy;  pinna of ear, epiglottis, auditory/eustachian tubes; Provides strength/elasticity but does not disperse loads or protect from mechanical stress/compression

  Cells dispersed in ground substance, but interwoven with elastic collagen fibers (found in pinna of ear, auditory tubes, epiglottis, larynx)
• difference between elastic cartilage and hyaline

  perichondrium

  similarity: the dispersal of chondrocytes within lacunae in the ground substance
• perichondrium

  Elastic cartilage has a perichondrium (similar to periosteum of bone), which has blood vessels and consists of two layers:  inner layer helps in formation of chondroblasts for regeneration; outer layer is fibrous and produces collagen fibers.
• what is mechanically inferior to hyaline cartilage

  fibrocartilage: -Highly resistant to compression because it has a much higher concentration of tightly braided collagen fibers and much less ground substance than AC (less water to move out of the tissue)

  less shock absorption than hyaline

  ideal for repeated low load
• articular hyaline cartilage


  no perichondrium=no ready source of fibroblasts for repair (so if it gets significantly damaged, it won’t regenerate = osteoarthritis)

  avascular

  mostly aneural
• articular cartilage regeneration

  Chondrocytes within the lacunae (pockets in the ground substance) can undergo mitosis (provides new cells for regeneration of tissue)
• articular cartilage nutrition: "milking action"

  •Cells (chondrocytes) surrounded by synovial fluid

  •Synovial fluid contains nutrients needed by cartilage

  •Cells imbibe synovial fluid (and nutrients) when the joint is unloaded

  •Cells expel fluid and metabolites when the joint is loaded

  •Optimal stimulus:  loading/unloading with gliding
• function of articular cartilage

  reduce friction: lubrication (Reduces wear/heat associated with tissues gliding on one another.  Lubricin, which is expressed by superficial zone chondrocytes at the cartilage surface, is responsible for the near frictionless state that exists between the joint surfaces)

  disperse loads (Healthy articular cartilage disperses compressive loads across the subchondral bone, reducing the stress experienced at any one point in the bone)
• STZ (superficial tangential zone)

  cells are flatter, smaller, and packed more closely together (more concentrated), and the cells and collagen fibers are arranged parallel to the articular surfaces (transverse orientation). The collagen fibers in this zone undergo tensile stress along their orientation line when the cartilage is compressed. This zone is also the most permeable (allows the most water movement in/out of the tissue)

  Increased permeability is likely due to decreased proteoglycan content and increased “free” water content
• middle zone of articular cartilage

  chondrocytes (cells) are more rounded; collagen fibers are arranged oblique to the articular surface
• deep zone of articular cartilage

  chondrocytes are rounded; collagen fibers are vertically oriented and are anchored into the calcified zone (binds cartilage to subchondral bone
• calcified zone of articular cartilage


  Calcified cartilage that provides a transition from cartilage proper to subchondral bone
• tidemark of articular cartilage

  Diffusion barrier.  Border of calcified zone that acts as a diffusion barrier in adults—doesn’t allow nutrients and gases to cross from vascularized bone into the cartilage (why nutrition only comes from synovial fluid).
• extracellular matrix


  (ground substance, PGs and collagen)

  Fibrillar (proteins) (having fibers--fibrous): collagen/elastin

  Interfibrillar (ground substance) (elements between fibers; provide support to fibers): PGs/water and dissolved electrolytes
• AC collagen (fibrillar) composition

  –70% of Dry weight ( 10-30% of wet weight)

  –Type II collagen most prevalent (maintains shape better than Type I)

  –AC 90-95% Type II collagen

  –Strength of steel!

  •Little resistance to compression

  •Very strong in tension: primary component providing tensile properties
• AC elastin (fibrillar) elastin


  no triple helix

  rubber-like elastic fibers

  uncoils when stretched, then recoils (like a spring)

  makes up a smaller proportion of fibrous components
• proteoglycans (interfibrillar)


  •PGs (aka Glycoproteins)

  •The number and types of GAGs attached determine the function

  • The whole structure is a PG. The feathers are the GAGs

  •Negatively charged

  –Attracts water (via GAGs)

  •Large swelling pressure—occupies larger space & spreads out

  •Pushes against collagen—collagen pushes back

  -enhances rigidity/structure of tissue

  mucopolysaccharide= ground substance= PG +H2O
• biphasic property of articular cartilage

  Fluid (1st)

  :  interstitial water—absorbs the first, rapid onset of force

  •Incompressible (under rapid load)

  •Stress goes first to fluid

  Solid (2nd)

  :  cells, collagen, GAG, PG’s—absorbs the longer duration forces

  •Incompressible elastic material

  •Stress goes second to solid

  •Free fluid leaves cartilage (hoop stress)
• Solids and water can’t be compressed, yet cartilage compresses.  How?  Fluid moving out into the synovial cavity.
• AC response to compression

  pushes fluid out of GAGs

  more repelling of neg charges, because they are closer together

  Shortened distance between two negatively charged particles = more resistance to compression
• AC response to tension

  compressive force -> increased fluid pressure -> increased tension in collagen fibers (hoop stresses) -> hoop stresses keep AC contained during compression

  Since all the cells, fibers, and GAGs are bound together, a force on one component is a force on them all

  Articular cartilage as a whole doesn’t really undergo tension, but compressive forces induce tension in the collagen tissues via hoop stress
• AC responses to shear

  •Shear occurs with forces parallel to surface

  •Highest shear forces in deep zone near tidemark (why?)

  stiffness in shear directly proportional to the amount of collagen

  Shearing stresses are most predictive of crack formation in the cartilage tissue.
• AC failure "age related changes"


  Depends on age
• RATE OF LOADING


  • Slow: PGs are attached to collagen and restrain rotation of collagen. When loads are slow, collagen can rotate in line of pull, dispersing forces
  • Fast: No time for rotation and dispersal of forces (reach yield point sooner with same level of stress—steeper stress-strain curve)-Faster loading damages deeper zones while slower loading damages superficial zones
• # OF LOADING CYCLES (cumulative trauma)

  Takes fewer cycles of same load at increased ages; increased stress (load) = decreased # of load cycles to cause failure; OR: lower stress (load) = more cycles to failure
• osteoarthritis and AC


  •Unstable joints lead to OA: 

  –Altered forces

  –Loss of proprioceptive input

  •Repetitive loads lead to OA:

  –Torsion

  –high impact (impulse)

  •Walking:  rapid heel strike worse than slower–Not necessarily the activity, but the way it is performed that increases likelihood of OA
• osteoarthritis

  Decreased PG content

  = increased H2O (percentage) and decreased stiffness (loss of solid component)

  = increased permeability

  = increased and more rapid deformation

  = Osteoarthritis
• how to help OA

  Increase GAG, biochemical adaptation, fluid movement = nutrition (and expulsion of metabolites)
• Cartilage is a highly adaptable tissue that protects joints from wear and tear.
• Cartilage requires both fluid and solid phases to accomplish the dispersion of forces.
• Disruption in these phases leads to arthritis.
• PT can influence cartilage regeneration through appropriately applied forces.
• structural organization of muscle

  muscle (deep fascia, epimysium)

  fascicle (perimysium)

  muscle fiber (endomysium)
• "mysiums"


  stores PE

  structure

  protection of neurovasculature
• muscle fiber (myofibril) = muscle cell


  surrounded by sarcolemma; inside is sarcoplasm, mitochondria, etc.

  Contractile proteins:  actin and myosin

  Structural proteins:  generate passive tension, support and align, transfer forces generated
• deep fascia

  dense irregular CT

  Same type of connective tissue as a joint capsule (dense irregular)

  Binds single muscles, but also connects multiple muscles to each other

  functions:

  separates individual muscles

  binds together muscles with similar functions

  fill spaces between muscles

  forms sheaths to help distribute nerves, blood vessels, and lymphatic vessels  
• epimysium


  encases entire skeletal muscle

  deep to deep fascia

  binds all the fascicles together to form the entire skeletal muscle

  -Provide series and parallel elastic forces to add to the storing of energy when a muscle is stretched
• perimysium


  surrounds fascicle

  Dense irregular CT

  Organizes the fascicles

  Protects/distributes neurovascular bundles

  Passive stretch stores energy to increase force production