cartilage

Hyaline

mainly Type II collagen fibers (3x 1(II) – slightly different form than found in Reticular fibers), GAGs, proteoglycans, multi-adhesive glycoproteins, and aggrecans

Elastic

elastic fibers in addition to the matrix material of hyaline

Fibrocartilage

abundant Type I (2x 1 & 1x 2) collagen fibers in addition to matrix material of hyaline cartilage

hyaline gEneral

Most common type of cartilage, Strong, low friction surface

hyaline occurance

Ribs (ventral ends), long bones (articular surfaces), nose, larynx, trachea, bronchi, fetal skeleton

Macroscopic appearance hyaline:

Plates, columns, irregular masses Enclosed with fibrous perichondrium (exceptions) Solid, but flexible, cuts easily with knife Translucent, bluish to pearly (glassy)

hyaline microscopic

Cells embedded in clear or lightly staining matrix, perichondrium on non-articular surfaces

Perichondrium

Dense irregular connective tissue

Fibers densely interwoven Type I

collagen

More cellular near cartilage

Cells and fibers fade into cartilage

perichondrium is found in

elastic and non-articular hyaline cartilage (not found around fibrous or articular hyaline cartilage)

Matrix of Hyaline Cartilage

Stiff, basophilic, felt-work of fine collagenous fibrils, up to 80% water

hyaline cartilige Ground substance:

multiadhesive glycoproteins, proteoglycans (aggrecan), glycosaminoglycans, (chondroitin and keratan sulfate).Fibers: mostly Type II collagen (3x 1(II))

Cartilage Matrix is Rich in Aggrecan

Aggrecan is a proteoglycan monomer found in aggrecan-hyaluronan aggregates (see fig 6.17)The GAGs of aggrecan are *chondroitin sulfate and keratan sulfate* (attached to protein core) Large negative charge attracts water (60-80% of weight is water), facilitates diffusion 100 to 200 aggrecan molecules linked non-covalently to hyaluronic acid (via multiadhesive proteins), huge complexes

Cartilage

Bears weight and provides rigidity, but flexible avascular, Consists of cells (chondrocytes), fibers, and ground substance.

what are the 3 types if cartilage

Hyaline, Elastic, Fibrous

Elastic

elastic fibers in addition to the matrix material of hyaline

Fibrocartilage

abundant Type I (2x 1 & 1x 2) collagen fibers in addition to matrix material of hyaline cartilage

How do cells get nutrients if the tissue is avascular?

Cartilage lacks intrinsic blood vessels - (no capillaries), lymphatics, nerves. Nutrients seep through matrix Metabolic requirements low –diffusion adequate for the needs of chondrocytes. Dyes quickly permeate living cartilage

Chondrocytes

Cells of mesenchymal origin, produce/maintain

matrix of cartilage, up to 40 m in diameter

Found in lacunae within the matrix, alone or in isogenous group (recently divided) May produce metaloproteases (remodeling) Cytoplasm basophilic if actively producing proteoglycans, otherwise acidophilic in most cells Clearer cytoplasm = fat droplets, glycogen granules

Chondrogenesis

mesenchymal cells enlarge and form crowded group, cells vesicular. Cells produce mucinoid fluid = precartilage. Plates of matrix form between cells (honeycomb), now called chondrocytes. Surrounding mesenchyme compresses to become perichondrium, Growth Interstitial or Appositional(in the head region formed from ectomesenchymefrom neural crest)

Interstitial Cartilage

Growth

Forms new cartilage within existing cartilage. Cells divide within lacunae. Cells deposit matrix, which leads to separation of cells . Interstitial growth confined to young cartilage

Capsular (pericellular) matrix:

Youngest matrix nearest chondrocytes. Stains most darkly, contains more sulfated proteoglycans, hyaluronic acid, multi-adhesive proteins

Territorial (chondrin ball) matrix:

Stains less darkly but darker than general matrix.Lower concentration of sulfated proteoglycans

Interterritorial (general) matrix:

Surrounds territorial matrix, rich in glycoproteins and proteoglycans, most lightly staining

Adult chondrocytes have very limited ability to divide, limited ability for repair

Perichondrium can proliferate to fill defect/gap

how does periclndrium repair defect/ gap

fibroblasts transform into chondroblasts, chondroblasts deposit new matrix on surface of old matrix

Regression of Cartilage

With age chondrocytes die, matrix basophilia declines, stains less darkly. Matrix becomes opaque, hard, brittle; may calcify(Note: calcified cartilage is a temporary step in endochondral bone formation

Elastic Cartilage Occurrence

External ear (auricle) ,Eustachian tube (outer part), Epiglottis

Elastic Cartilage Macroscopic appearance

Yellow, more opaque than hyaline .More flexible & elastic than hyaline .Perichondrium same as hyaline

elastic microscopi structure

Cells single or in groups, capsules around cells, more cell dense than hyaline. Matrix of hyaline cartilage, with addition of a branching meshwork of elastic fibers that vary in thickness

What type of stain is best for elastic cartilage

Orcein, Verhoeff, Van Gieson, or Welgert’s stain

Fibrocartilage

Resistant to compression & shearing, Combo of dense regular (or irregular) CT and hyaline cartilage. Type I and II collagen Little ground substance, mostly fibrous

Occurrence

Intervertebral disks, pubic symphysis, some in articular cartilages & capsules, where tendons attach to bones

fibrocartilage occurance

Intervertebral disks, pubic symphysis, some in articular cartilages & capsules, where tendons attach to bones

fibrocartlage best stain

Mallory’s, Masson’s, Alcian Blue

Fibrocartilage Macroscopic Appearance:

Firm, fibrous, no perichondrium

fibrocartlage Microscopic Structure

Single cells, in groups, or in rows, Coarse collagenous fibers (Type I & II) interweave (pubic symphysis) OR parallel with cells between fibers where high tensile strength needed (intervertebral discs)

fibrocartilage Never occurs alone

merges with hyaline cartilage or surrounding fibrous tissue