CARTILAGE A DENSE CONNECTIVE TISSUE

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CARTILAGE A DENSE CONNECTIVE TISSUE Bears
weight and provides rigidity Consists of cells,
fibers, and ground substance Three types of
cartilage Hyaline, Elastic, Fibrous
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HYALINE CARTILAGE Fundamental type and most
common Occurrence Ribs (ventral ends) Long
bones (articular surfaces) Nose, Larynx,
Trachea, Bronchi External auditory meatus
(part) Fetal skeleton (except membrane bones)
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Macroscopic appearance Plates, columns,
irregular masses Solid Flexible, elastic (but
less than elastic cartilage) Cuts easily with
knife Translucent Bluish to pearly
(glassy) Enclosed with fibrous envelope
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Microscopic structure Cells embedded in clear
matrix Perichondrium on surface
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PERICHONDRIUM Dense fibrous connective
tissue Fibers densely interwoven
(collagenous) More cellular near
cartilage Cells and fibers fade into cartilage
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CELLS Chondrocytes (up to 40 µ) Spherical ?
flattened near perichondrium and joint
surfaces cytoplasm basophilic fat droplets,
glycogen granules single in young cartilage,
groups in older cartilage (2, 4, 8, etc.)
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MATRIX Appears homogeneous Stiff, basophilic,
feltwork of fine collagenous fibrils Space
(lacunae) Composition of Matrix 70
water Ground substance includes
proteoglycans, glycoproteins,
Chondroitin sulfate
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AREAS WITHIN MATRIX Cartilage capsule
(matrix) youngest matrix nearest
chondrocytes most basophilic Territory (Chondrin
ball) less basophilic but more than general
matrix higher content of chondromucoids and
chondroitin sulfate General matrix rich in
glycoproteins and proteoglycans
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Matrix rich in aggrecans large proteoglycan
molecules Protein core Glycosaminoglycans
(chondroitin 4-sulfate and chondroitin
6- sulfate) attach to protein cores 100 to
200 aggecan molecules linked non-covalently to
hyaluronic acid huge complexes (3 4 micons
long) Negative charges (proteoglycan) attract
Na
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Aggrecans, cont. Negative charges of Na attract
water molecules Aggrecans greatly hydrated
(up to 80 water) Fills interstices between
collagen fibers electrostatic bond with
collagen
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NUTRITION Cartilage lacks intrinsic blood
vessels, lymphatics, nerves Nutrients seep
through matrix Metabolic requirements low
diffusion adequate for needs
Dyes quickly permeate living cartilage
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DEVELOPMENT AND GROWTH OF CARTILAGE Mesenchymal
cells enlarge crowded group, cells
vesicular Cells surrounded by mucinoid fluid
Precartilage Plates of matrix form between cells
(honeycomb) Cells ? chondrocytes Surrounding
mesenchyme compresses ? fibrous
perichondrium Continued growth Interstitial or
Appositional
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INTERSTITIAL CARTILAGE GROWTH Cells in matrix
divide (mitotic) 2, 4, 8, etc. cells Additional
deposition of matrix separates cells
(capsules) Capsule newly formed matrix Forced
away with new growth/deposition Older matrix
merges/becomes territory Matrix of territory
later forced further away ? general
matrix Intersitital growth confined to young,
expansile cartilage
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APPOSITIONAL CARTILAGE GROWTH Growth from
perichondrium Innermost fibroblasts ?
chondroblasts Chondroblasts ? chondrocytes Depos
it matrix Chondrocytes surrounded with
matrix New layer of cells recruited from
perichondrium Process repeats Continues to full
maturity of cartilage mass
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Regression With age chondrocytes die matrix
basophilia declines Old age Cartilage may
calcify (calcification) Matrix becomes opaque,
hard, brittle Calcified cartilage is also
temporary step in endochondral bone formation
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Elastic Cartilage Occurrence External ear
(auricle) Auditory tube (outer
part) Epiglottis Larynx (corniculate,
cuneiform, arytenoid (part) cartilages)
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Macroscopic appearance Yellow More opaque than
hyaline cartilage More flexible and elastic than
hyaline cartilage Perichondrium externally (same
as hyaline cartilage)
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Microscopic Structure Fundamentally like hyaline
cartilage Cells single or in groups Capsules
around cells like hyaline cartilage Matrix
contains ground substance and masked fibers
(collagenous) Also branching meshwork elastic
fibers Elastic fibers vary (thickness,
abundance) in different masses Interior of
cartilage mass elastic fibers thicker and
coarser
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Fibrocartilage Occurrence Intervertebral
disks Pubic symphsis Articular cartilages and
capsules Lining tendon grooves Insertions of
tendons and ligaments (some)
Intervertebral disc (Rat). C chondrocytes
(HE/Alcian Blue)
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Fibrocartilage never occurs alone! Merges with
hyaline cartilage or surrounding fibrous tissue
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Macroscopic Appearance Firm, Fibrous, No
perichondrium Microscopic Structure Ordinary
cartilage cells single, groups, or rows Matrix
? obvious, coarse collagenous fibers Fibers
interweave ? irregular pattern Tensile strength
needed ? parallel with cells between
fibers Intensely staining capsules Little
hyaline type matrix visible
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Note rows of chondrocytes and direction of fibers
(stress/tension lines)
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REGENERATION OF CARTILAGE Injuries not repaired
by the cartilage Adult cells likely do not
divide or have very limited ability Perichondr
ium proliferates t fill defect/gap Fibroblasts
transform into chondroblasts Chondroblasts
deposit new matrix Fractures may be united by
permanent fibrous tissue Fibrous tissue may be
replaced by bone.