| A | B |
|---|
| matrix of cartilage | consists mainly of collagen and elastin fibers embedded in ground substance |
| ground substance of cartilage | highly specialized consisting of large carbohydrate-protein molecules (proteoglycans) suspended in water |
| water is the...of cartilage | chief constituent |
| hyaline (articular) cartilage | most abundant cartilage of the body. comprises articular cartilage in synovial joints |
| fibrocarilage | has very dense network of collagen fibers arranged parallel to each other in several layers. strong material with little elasticity. found in certain joints to improve congruity |
| elastin cartilage | dominated by elastin fibers and thus has a moderate to high degree of elasticity. found in larynx, inner ear and eustachian tube |
| function of articular cartilage | transfers forces between articulating surfaces, distributes forces to joints to minimize stress, allow relative movement between surfaces with min friction(COF=0.0025) |
| morphology (makeup) of articular cartilage | thin layer of fibrous connective tissue. consists of cells (5%) and an intracellular matrix (95%) which is mostly water |
| cells of articular cartilage | called chondrocytes are metabolically active |
| matrix of articular cartilage | consists of structural macromolecules and tissue fluid. tissue fluid (60-80%) and structural macromolecules (20-40%). structural macromolecules are collagen, proteoglycan, and other proteins |
| tissue fluid | mostly water found in form of viscous gel. most fluid is free to move in and out of cartilage. closely associated with synovial fluid. fluid closely associated with proteoglycans. pores of cartilage are small inhibiting any rapid escape of fluid when cartilage is compressed (for shock absorption). low permeability enables cartilage to maintain its stiffness under compression |
| structure of articular cartilage | structurally heterogeneous. changes with depth from the joint surface. superficial zone, transitional zone, radial zone, calcified zone. |
| superficial zone | two layers (surface and deeper layer). surface layer has flat bundles of crimped collagen fibers. deep layer has dense collagen fibers lying parallel to joint surface. contains high percentage of water |
| transitional zone | contains large diameter of collagen fibers that lei parallel to the joint surface (less parallel than in superficial zone) |
| deep zone | large numbers of large collagen bundles running perpendicular to joint surface. high proteoglycan content. water content is low |
| calcified zone | marks transition for cartilage to stiffer subchondral bone. collagen fibers from deep zone anchor the cartilage to the bone by fixing themselves into the subchondral bone |
| structure collagen | accounts for much of structure of cartilage. gives cartilage much of its tensile stiffness and strength. offers little resistance to compression (buckles in compression) |
| structure proteoglycan | are glycoproteins. present in connective tissue. bc of their molecular structure are resistant to compressive forces |
| tensile properties | vary from one structural zone to another due to different orientations of collagen fibers. are highly anisotropic. tensile strength higher parallel to split line than perpendicular direction. tensile modulus decreases with increasing depth bc of the orientation of collagen fibers. properties of cartilage with respect to tensile loads far less than for tendon or ligament (cartilage contains less collagen) |
| compressive properties | vary with the zone tested. related to proteoglycan concentration. when proteoglycan content increases, compressive stiffness also increases. proteoglycan content greater in deeper zones |
| shear properties | not yet measured with respect to depth of tissue. interactions of solid components of matrix are responsible for these properties. may put collagen fibrils under tension |
| water movement in cartilage | when cartilage is subjected to lad water is forced out of the cartilage and the cartilage deforms. the rate and extent of the deformation depends on the size and duration of the load. when the load is removed, the proteoglycans restore original level of water. the ability to deform and restore is called viscoelasticity |
