Download The extracellular matrix (ECM)

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The extracellular matrix (ECM)
Tissues & cells are surrounded by
Extracellular matrix: ground substance, fibers
And water
Ground substance:
-glycosamino glycans
-adhesive glycoproteins
Functions of ground substance:
-resist compression
-retard movement of bacteria and metastatic cells
-filtration barrier for diffusable signaling factors
-binding site for contact signaling factors
Sulfated - chondroitin-4-sulfate, keratin sulfate,
Heparin sulfate, heparin
Not sulfated - Hyaluronic acid
-long unbranched polysaccharides
-repeating disaccharide units,
the amino sugar N-actylglucosamine
and uronic acid
-long unbranched polysaccharides
-repeating disaccharide units
-the amino sugar N-actylglucosamine and uronic
Sulfated sugars attract carboxyl groups (neg
charged), these bind onto to Na,  attracts
water resists compression
-sulfated glycoamino glycans and a protein core
-cover huge areas of extracellular matrix
- eg. Aggrecan in cartilage and other connective tissues
-contains hyaluronic acid + link protein + core protein
Collagen attaches to the proteoglycans
Pathogenic bacteria (S. aureus)
secrete hyaluronidase,
--> destroys extracellular matrix
Adhesive Glycoproteins
Cells can adhere to the ECM molecules
Adhesive glycoproteins bind to integrins surface proteins
eg. Of glycoproteins
Fibronectin is on fibroblasts.
-has binding sites for hyaluronic acid and other
-has binding sites for collagen (an extracellular
fibrous protein)
-has amino acid sequences for binding onto the
cell membrane (arg, gly, asp)
-anchors fibroblasts to the ECM
-marks migratory pathways for progenitors
Extracellular protein fibers:
Collagen fibers
Elastic fibers
Reticular fibers
Collagen is very tough and fibrous
Collagen is very tough and fibrous, how?
• Fibers fibrils made of tropocollagen
• 3 polypeptide chains, triple helix
• many H bonds across chains
Collagen is very tough
-has strong tensile forces
-makes up about 20% of the body
-with H & E stain, appear pink (acidophilic)
-no color if not stained
-each collagen fiber is 10 mm wide
• At least 15 types of collagen
• Type I – coarse thick filaments, Ct dentin
• Type II – fine fibers, hyaline and elastic
• Type III – reticular, glycosylated
• Type IV – BM, not fibrillar