chapter 7 - ECM notes.docx

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Biological Sciences
Rene E Harrison

EpidermisThe outer layer of skin the epidermis is a type of epithelial tissuethe epidermis consists largely of closely packed cells attached to one another and to an underlying noncellular layer by specialized contactsThese contacts provide a mechanism for cells to adhere to and communicate with one another Dermisthe deeper layer of the skin the dermis is a type of connective tissueExtracellular MatrixMany types of animal cells are surrounded by an extracellular matrix ECMan organized network of extracellular materials that is present beyond the immediate vicinity of the plasma membraneThe ECM is more than an inert packing material or a nonspecic glue that holds cells together it often plays a key regulatory role in determining the shape and activities of the cellOne of the best dened extracellular matrices is the basement membrane or basal lamina a continuous sheet 50 to 200 nm thick that 1 surrounds nerve bers muscles and fat cells 2 underlies the basal surface of epithelial tissues such as the epidermis of the skinECM is mostly composed of macromoleculesMost proteins of the extracellular space are typically extended brous species These proteins are secreted into the extracellular space where they are capable of selfassembling into an interconnectedthreedimensional networkthe proteins of the ECM serve as trail markers scaffolds girders wire and glueCollagen An ECM proteinCollagens comprise a family of brous glycoproteins that are present only in extracellular matricesCollagens are found throughout the animal kingdom and are noted for their high tensile strength that is their resistance to pulling forces It is estimated that a collagen ber 1 mm in diameter is capable of suspending a weight of 10 kg 22 lb without breaking Collagen is the single most abundant protein in the human bodyCollagen is produced primarily by broblasts the cells found in various types of connective tissues and also by smooth muscle cells and epithelial cellsTo date 27 distinct types of human collagen have been identiedAll collagen molecules are trimers consisting of three polypeptide chains called alpha chainsAlong at least part of their length the three polypeptide chains of a collagen molecule are wound around each other to form a unique rodlike triple helixThe alpha chains of collagen molecules contain large amounts of prolineA number of the collagens including types I II and III are described as brillar collagens because they assemble into rigid cablelike brils which in turn become packaged into thicker bers that are typically large enough to be seen in the light microscopeAmong the various components of the ECM collagen molecules provide the insoluble framework that determines many of the mechanical properties of the matrixNot all collagens form brils
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