How is the small intestine adapted for efficient absorption?

Diffusion is the main mechanism for absorption within the small intestine, so effective diffusion is the key to sufficient nutrient absorption. The small intestine has a very large surface area, created by folds and the presence of villi and microvilli. These are finger-like projections from the inner cells of the intestine which are only one-cell thick, allowing for a short diffusion distance between the intestinal lumen and surrounding capillaries. The vast network of capillaries surrounding the small intestine (located within the villi) ensures a constant concentration gradient is maintained, which also increases the rate of diffusion.