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Diffuses between blood and cells and through which

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diffuses between blood and cells and through whichmacrophages and white blood cells move.Mature connective tissues include loose connective tis-sue, dense connective tissue, cartilage, bone, and blood.The connective tissue types have different connective tis-sue cells that form the extracellular matrix. The extracellu-lar matrix ofloose and dense connective tissuesis formedbyfibroblasts(-blastearly, developing stage); the ex-tracellular matrix ofcartilageis formed bychondroblasts(chondro-cartilage) and maintained bychondrocytes;and the extracellular matrix ofboneis formed byosteoblasts(osteo-bone) and maintained byosteocytes.Plasmais the extracellular matrix in which blood cells andplatelets are suspended; however, plasma is not made bythese cells.1.Loose Connective TissueLoose connective tissue includes areolar, reticular, and adi-pose tissues. Inloose connective tissue,the fibers in theextracellular matrix are loosely arranged. Collagen, elastic,and reticular fibers in this tissue provide strength, elastic-ity, and support. Ground substance is semi-fluid (viscous),but interstitial fluid can easily diffuse through it. Fibro-blasts and adipocytes (lipid-storing cells) permanentlyreside in the tissue. Cells that are involved in body defense,such as macrophages, mast cells, and white blood cells,enter connective tissue from blood vessels that traversethrough the extracellular matrix.Areolar connective tissueis the most abundant con-nective tissue. It contains fibroblasts, all three fiber types,a semi-fluid (viscous) ground substance, and a variety ofcells involved in body defenses.Reticular(reticulo-net-like)fibersare the dominant fiber type inreticularconnective tissue. Reticular cellssynthesize the reticularfibers and the ground substance. Reticular cells are actuallyfibroblasts, but they synthesize more reticular fibers thancollagen fibers.Adipose(adipo-pertaining to fat)tis-sue,like areolar connective tissue, contains fibroblasts,fibers, ground substance, and adipose cells. However, adi-pose tissue has a greater number ofadipocytes(lipid-storing cells) and very little extracellular matrix. Lipidwithin the adipose cells occupies most of the cell volumeand pushes cytoplasm and organelles to the periphery.Some slides do not have the lipid stained, or the lipid hasbeen removed during tissue preparation. In those slides, thenucleus and cytoplasm are stained, and the space inside thecell normally occupied by lipid appears “empty.”2.Dense Connective TissueThe extracellular matrix of dense connective tissue ispacked with fibers and contains very little ground sub-stance and few fibroblasts. Indense regular connectivetissue,the extracellular matrix is packed with parallel bun-dles of collagen fibers that run in the direction of thepulling forces applied to the tissue. Fibroblasts aresqueezed between the bundles, and the cytoplasm extendsbetween and around collagen bundles. Collagen fibers giveunstained tissue a silvery white appearance, which is why

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