Final answer:
Villi and microvilli increase the surface area of the small intestine, enhancing absorption efficiency. Villi are folds lined with absorptive cells, while microvilli are small projections on these cells that further increase the surface.
Step-by-step explanation:
Villi and microvilli are critical features in the small intestine that aid in the absorption of nutrients. The villi are folds in the lining of the small intestine that increase the available surface area for absorption. Each villus is covered in microvilli, which are tiny projections that further maximize the surface area. This increased surface area is crucial because it allows for more efficient absorption of nutrients by diffusion.
The absorptive cells that line the small intestine are packed with microvilli. These small projections extend the plasma membrane and create a larger surface for interaction with digested food, thereby enhancing the uptake of nutrients, including bile salts and vitamin B12. The large surface area presented by both villi and microvilli is supported by a rich supply of blood vessels, which transport the absorbed nutrients throughout the body.
Efficiency of Nutrient Uptake
This expanded surface area provided by the finger-like shape of the villi and microvilli greatly increases the efficiency of nutrient uptake. The microvilli are particularly effective because they not only expand the surface area but also are specifically located on the area of the plasma membrane facing the cavity from which substances are absorbed, thus optimizing their exposure to available nutrients.