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Cartilage and bone arespecialized connective tissues.

Like all connective tissues, cartilage andbone consist of

cells

extracellular matrix.

The matrix of all CTs consists of

fibers (collagen, reticular, and elastic)

amorphous ground substance, which contains

proteoglycans

hyaluronic acid

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WHERE THEY ARE PRODUCED ?

The matrix is secreted by some of the cells inconnective tissues, fibroblasts in most CTs

In cartilage, it is chondroblasts and chondrocytesthat produce the matrix

while in bone, it is osteoblasts and osteocytes.

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Cartilage

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 protein withnumerous- about 100- glycosaminoglycans(GAGs) attached bottle-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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Cartilage

In cartilage, the GAGs attached to the coreproteins are chondroitin sulfate and keratansulfate.

The proteoglycans themselves are attached, byspecial linker proteins to long, rigid molecules ofhyaluronic acid (HA)

About eighty proteoglycans are attached to onemolecule of HA

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Cartilage

The repeating units of chondroitin sufate are D-glucoronic acid and N-acetylgalactosamine-(4 or6)-sulfate

The repeating units of keratan sulfate aregalactose or galactose 6-sulfate and N-acetylglucosamine 6-sulfate.

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

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

and this large component of water accounts forthe resilient nature of cartilage

Cartilage is poorly vascularized, and gets most ofits nutrients through diffusion. In the adult, repair

is poor.

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Three kinds of cartilage

Hyaline cartilage

Elastic cartilage

Fibrocartilage.

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BONE Consits

60%

35%

5%

Mineral

Matrix

Cells

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Bone

Bone is both

resilient ( due to the organic matter (collagen)

hard (due to the inorganic minerals)

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There are two kinds of mature bone

1.compact bone

2.spongy bone

Compact bone and spongy bone are found in specific locations.

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compact bone

Compact bone is also called dense bone andcortical bone

composed of cylindrical structures called osteonsor Haversian systems

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spongy bone

Spongy bone is also called cancellous bone,trabecular bone and medullary bone

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Compact bone and spongy boneare found in specific locations.

1. In long bones , most of the thickness of thediaphysis is made of compact bone ,with a smallamount of spongy bone facing the marrow

cavity.

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Control of calsium homeostasis

Calsium is present in the plasma in the threeforms.

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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Control of calcium

The plasma concentration of calcium is controlledby PTH

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

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PTH (PARATHYROID HORMONE)

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Example of a NegativeFeedback Loop:

Homeostasis