A fabric whose weave is slack is less resistant to strain than one whose knit is close. These physical principles of toughness are followed by Nature all the way down the molecular scale. At the cellular level, protrusions known as microvilli grow at the apical end of the epithelial cells that line the intestinal tract. Each protrusion is like a finger dipping into the gut lumen. There can be up to one thousand protrusions on the end of each cell, which together form a fuzzy lining that looks like the bristles of a very long brush, hence its name: the brush border. These protruding digits are not free to wiggle as they wish however. Each protrusion is linked firmly to neighbouring protrusions thus making the whole system tougher in a realm - digestion - where tissues can undergo severe mechanical insults. But you need something to tighten the mesh. This is performed by proteins that belong to a family known as the cadherins, namely cadherin-related family members 2 and 5.
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