The appearance, ultrastructure and function of microvilli.

Microvilli are tiny protrusions that help to increase surface area. Epithelial cells in the small intestine need have these in order to increase the rate of diffusion: there is a bigger surface area so more things can diffuse at the same time.

They are also thin walled to decrease the diffusion distance and so increase the rate of diffusion. This is key in the small intestine so that all the useful molecules from food eaten can be absorbed by the cells before the food moves on.

Under a light microscope the microvilli in the intestines are so tightly packed they look like a bush and are referred to as a 'bush border'.

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Not to scale