How does the small intestine work in the absorption of nutrients into the blood?
By the time that food has reached the small intestine, it has already been exposed to enzymes that will break down both carbohydrates and proteins. Saliva in the mouth contains alpha-amylase to break down carbohydrates, and the stomach contains enzymes like pepsin to break down proteins. In the small intestine the food is broken down further still by other dietary enzymes. Bile is also introduced to emulsify fats that have entered. The small intestine is lined with microvilli, who’s funciton is to increase surface area of the small intestine and to absorb nutrients from the incoming food. This means that the small intestine is permeable to these nutrients. Things such as free fatty acids, amino acids, and simple sugars pass through the small intestine, and into vascular that surrounds the small intestine and carries the nutrients to the liver for further processing.
