Understanding Nutrient Absorption: The Role of the Small Intestine

The third stage of digestion is absorption, which begins when food enters the small intestine. The small intestine is a long, coiled tube that is responsible for most of the absorption of nutrients from food. The walls of the small intestine are lined with tiny villi, which are finger-like projections that increase the surface area of the intestine and help to absorb nutrients. The villi are covered in microvilli, which are even smaller projections that further increase the surface area of the intestine.

The absorption of nutrients from food occurs through a process called active transport. Active transport requires energy in the form of ATP to move nutrients from the lumen of the small intestine into the bloodstream. Some of the nutrients that are absorbed in the small intestine include carbohydrates, proteins, fats, vitamins, and minerals.