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Histology Chapter 4

Main characteristics of the four basic types of tissues.
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Epithelial tissues are composed of closely aggregated polyhedral cells adhering strongly to one another and to a thin layer of ECM, forming cellular sheets that line the cavities of organs and cover the body surface. Epithelia (Gr. epi, upon + thele, nipple) line all external and internal surfaces of the body and all substances that enter or leave an organ must cross this type of tissue.
The connective tissue that underlies the epithelia lining the organs of the digestive, respiratory, and urinary systems
-Most epithelia are adjacent to connective tissue containing blood vessels from which the epithelial cells receive nutrients and O2.
- Even thick epithelia do not themselves normally contain blood vessels.
Type IV collagen: Monomers of type IV collagen self- assemble into a two-dimensional network of evenly spaced subunits.
Laminin: These are large glycoproteins that attach to trans-membrane proteins called integrins at the cells' basal surface and project through the network of type IV collagen.
■ Nidogen and perlecan: Respectively a short, rod-like protein and a proteoglycan, both of these cross-link laminin to the collagen network and help determine the porosity (porous) of the basal lamina and the size of molecules able to filter through it.
- structural support for epithelial cells
- attach epithelia to underlying connective tissue
- Basal lamina components help organize integrins and other proteins in the plasma membrane of epithelial cells, maintaining cell polarity and helping to localize endocytosis, signal transduction, and other activities.
- mediate many cell-to-cell interactions involving epithelia and mark routes for certain cell migrations along epithelia.
- serves as a scaffold that allows rapid epithelial repair and regeneration.