The small intestine is the longest part of the alimentary canal because it is responsible for the majority of nutrient absorption. Its extensive coiling increases its surface area, facilitating efficient absorption of nutrients into the bloodstream.
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The small intestine is the longest part of the alimentary canal to maximize the surface area available for nutrient absorption. Its length, approximately 20 feet in humans, provides an extensive absorptive surface for the products of digestion. The inner surface of the small intestine is lined with numerous finger-like projections called villi and microvilli, which significantly increase the absorptive area. This large surface area facilitates the efficient absorption of nutrients, including carbohydrates, proteins, and fats, ensuring that the majority of digestion and nutrient absorption occurs in the small intestine. The elongated structure optimizes the digestive process and nutrient extraction.