Cartilage and Bone
Last Modified: 2016-03-08
· Origin: Formed from mesenchyme during 5th week of development.
· Importanceo Specialized connective tissue
o Consistency of ECM allows it to bear mechanical stress w/o permanent distortion.
o Firmness, elasticity, and tensile strength.
o Shock absorbing function, forms smooth surfaces of synovial joints (hyaline cartilage) o Development of fetal skeleton and most growing bones.
· Avascular: Nutrition by diffusion. Difficulty of regeneration.
· Growth: Appositional (from surface) & Interstitial (from the inside).
· Poor ability for regeneration. Usually occurs with formation of fibrous scar.o Collagen lays down lots of fibroblasts into tear in cartilage and seals it to make scar rather than regrow cartilage.
§ Dense Irregular connective tissue.
§ Allows for blood, nerve & lymph vessel passage
§ Actively secreting cartilage matrix (abundant RER & Golgi).
§ Responsible for appositional growth.
§ Highly hydrated
Produce and maintain ECM
§ Large, Rounded. Capable of mitosis.
§ Large, Euchromatic nucleus.
§ Produce GAGs and Collagen type II
§ Dividing chondrocytes form clusters called isogenous groups.
§ Actively dividing: Completely surrounded in matrix. Fairly actively secreting material. Capable of mitosis.
Push matrix to side when divided.
· Thin fibrils,
no fibers or bundles.
· Banding in TEM.
· Mechanical stability and tensile strength.
GAGs and proteoglycans
· Hyaluronic acid: Long. Bind non-covalently through link protein to proteoglycans form giant complexes.
Large (-) charge
Bind water forming a hydrated gel. · Chondroitin Sulfate: Covalently linked to core proteins to form proteoglycans.
Cross link collagen and proteoglycans
Attach ccytes to matrix
o Matrix around lacunae w/ chondrocytes has fewer collagen fibers and is richer in GAGs.
§ Territorial matrix: Stains intensely w/ basic dyes (hematoxylin)
o Interterritorial matrix: Between lacunae: Stains less intensely w/ basic dyes.
§ Perichondrium Absent from articular cartilages and epiphyseal plates.
§ Matrix composed primarily of collagen type II, GAGs and proteoglycans.
§ No visible fibers.
§ Chondrocytes in lacunae, arranged into isogenous groups.
Forms embryonic skeleton.
Serves as template for bony skeleton.
Forms articular surfaces of movable joints, epiphyseal plates, costal cartilages, and supports respiratory systrem (nose, trachea, bronchi, larynx).
§ No perichondrium on top of hyaline cartilage in joints.
Epiglottis is elastic cartilage.
§ Use Orsin stain, see lots of wispy, coiled elastic fibers.
§ Matrix composed of Collagen type II, Gags, proteoglycans and elastic fibers (visible in light microscope.
§ Matrix does not ossify.
§ Chondrocytes located in large, istended lacunae.
§ No perichondrium.
§ Can see bundles of collagen type I in light microscope
§ Matrix composed of collagen type II, type I, GAGs, and proteoglycans.
Coarse fibers and bundles of collagen type I can be visualized in light microscope.
§ I brings tensile strength. II brings elasticity.
§ Wide age range
§ Male predominancy
§ Pelvis, proximal femur, proximal humerus.
§ Slow Growing tumor.
§ Abundant cartilaginous matrix.
· Mineralized extracellular matrix.
· One of hardest tissues in body.
· Formed by collagen fibers, ground substance, and cells.
· Withstands compression, deformation, and stress
· Diffusion limited due to mineralized ECM.
· Vascular tissue w/ blood and lymph vessels running through ito Heals faster than cartilage.
Spongy or trabecular bone forms: Spicules/Trabeculae on inner side of bone; extends to marrow cavity
o External surface covered with periosteum. (dense irregular connective tissue) § Two layers: External fibrous layer (collagen fibers), Internal osteogenic layer (osteoprogenitor cells). o Internal marrow cavity lined with endosteum (thin layer of connective tissue w/ osteoprogenitor cells)
o Organic matrix: Dense irregular connective tissue
§ Large collagen type I bundles (tensile strength)
§ GAGs (chondroitin sulfate, keratan sulfate), bind covelantly to proteins to form large proteoglycan aggregates. Attach non-covalently to hyaluronic acid.
§ Multiadhesive proteins. (bind organic to inorganic components)
§ Little ground substance in bone matrix.
§ Derived from bone marrow, not mesenchyme.
§ Resorption of bone.
§ Attached to bone via actin-rich area: clear zone.
§ Direct contact with bone is ruffled border.
§ Secrete H+ ions, collagenase, and lysosomal enzymes.
§ Promote digestion of collagen and dissolving calcium phosphate crystals.
§ Depression in matrix caused by osteoclasts : Howship’s lacunae
Primary/Woven bone § Immature type of bone laid down when bones first formed or repaired. Collagen fibers irregular and interwoven.
Secondary/Lamellar bone · Collagen fibers organized into layers, lamellae. · Stronger than woven bone. ·
Structural unit: Osteon
o Zone of proliferation: Rapid tissue growth, division of chondrocytes ( columns of stacked cells/ isogenous groups) parallel to long axis of bone.
Zone of hypertrophy (swollen chondrocytes)
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