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3 partially restrict diffusion of substances through

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Unformatted text preview: eep them anchored as part of sheet, keep them from drifting away! 3) Partially restrict diffusion of substances through the epithelium, in either direction Help prevent material from diffusing willy nilly through epithelia! Capillaries never penetrate basement membranes of epithelia, i.e., epithelia are always avascular no matter how thick they are. GENERAL RULE OF EPITHELIA: NEVER VASCULARIZED THEMSELVES!!!!!!!! NEVER CROSS OTHER EPITHELIA -- CAN'T GROW THROUGH ONE ANOTHER. SO CAPILLARIES NEVER GROW TO AN EPITHELIA, NO MATTER HOW THICK THEY GET. NERVE FIBERS CAN CROSS EPITHELIA…BUT NEVER CAPILLARIES/BLOOD VESSELS. A basement membrane has two major parts: basal lamina and reticular lamina laminin, type 4 collagen assoc. with basal lamina -- and made by epithelia Important components of the basal lamina (BL) include: • laminin, attached to integrin proteins in the epithelial cell membranes • type IV collagen, forming a felt-like sheet associated with the layer of laminin • perlecan, a glycoprotein that helps lin...
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