Final answer:
The small intestine is the primary site for vitamin absorption due to its highly adapted structure, featuring villi and microvilli that increase the surface area for nutrient absorption.
Step-by-step explanation:
The small intestine is the primary site for vitamin absorption in the body. It is in the small intestine where the digestion of protein, fats, and carbohydrates is completed and where the absorption of nutrients, including vitamins, into the bloodstream occurs. This organ is specially adapted for this purpose with a highly folded inner surface that vastly increases the absorption area.
Structural features such as villi and microvilli maximize the efficiency of absorption. Each villus contains numerous microvilli, which collectively create a surface area about as large as a basketball court. This immense surface area facilitates the absorption of nutrients from the digested food into the bloodstream.
The small intestine is divided into three main sections: the duodenum, the jejunum, and the ileum. The villi, with their many folds and associated blood vessels, absorb nutrients which are then carried to the liver through the hepatic portal vein. The liver plays a vital role in regulating the distribution of these nutrients to the body and detoxifying certain substances.