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cellsextracellular matrix.

fibers (collagen, reticular, and elastic)

amorphous ground substance, which containsproteoglycans

hyaluronic acid

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The matrix is secreted by some of thecells in connective tissues, fibroblasts in

most CTs In cartilage, it is chondroblasts and

chondrocytes that produce the matrix

while in bone, it is osteoblasts andosteocytes.

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a solid connective tissue that is to a certainextent pliable, making it resilient

The ground substance of cartilage is rich inproteoglycans consisting of a core proteinwith numerous- about 100-glycosaminoglycans (GAGs) attachedbottle-brush fashion around it

GAGs are made of repeating units ofdisaccharides, one of which is always aglycosamine (hence the name) such asglucosamine or galactosamine

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In cartilage, the GAGs attached to thecore proteins are chondroitin sulfate and

keratan sulfate. The proteoglycans themselves are

attached, by special linker proteins tolong, rigid molecules of hyaluronic acid(HA)

About eighty proteoglycans areattached to one molecule of HA

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The repeating units of chondroitin sufateare D-glucoronic acid and N-

acetylgalactosamine-(4 or 6)-sulfate The repeating units of keratan sulfate are

galactose or galactose 6-sulfate and N-acetylglucosamine 6-sulfate.

The repeating units of hyaluronic acidare D-glucuronic acid and N-acetylglucosamine

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Between 60 and 80 percent of the netweight of (hyaline) cartilage is water

and this large component of wateraccounts for the resilient nature ofcartilage

Cartilage is poorly vascularized, and getsmost of its nutrients through diffusion. Inthe adult, repair is poor.

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Hyaline cartilage

Elastic cartilage

fibrocartilage.

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60%

35%

5%

Mineral

Matrix

Cells

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Bone is both

resilient ( due to the organic matter

(collagen) hard (due to the inorganic minerals)

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Bone serves as a storage site for calciumand phosphate

Blood calcium levels are regulated by thehormones parathormone (parathyroid

hormone), which raises blood calciumlevels by stimulating bone resorption, andcalcitonin, which reduces blood calcium

by suppressing bone resorption andincreasing osteoid * calcification

*Osteoid is the matrix secreted by osteoblasts and osteocytes prior to

mineralization

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1.compact bone

2.spongy bone

Compact bone and spongy bone are found in specific locations.

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Compact bone is also called densebone and cortical bone

composed of cylindrical structures calledosteons or Haversian systems

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Spongy bone is also called cancellousbone, trabecular bone and medullary

bone

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1. In long bones , most of the thickness ofthe diaphysis is made of compact bone

,with a small amount of spongy bonefacing the marrow cavity.

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Calsium is present in the plasma in thethree forms.

47 % is bound to proteins,principally albumin 46 % exist as free ions and the remainder is

complexed with phosphate and citrate.

The free ions are the only form that is physiologically active

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The plasma concentration of calcium iscontrolled by PTH

PTH is a polypeptide hormone synthesised in the parathyroid glands ,andcalcitriol.

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