The part of the digestive system primarily responsible for nutrient absorption is the small intestine. This organ is structured with villi and microvilli, which increase surface area, allowing for efficient absorption of nutrients like carbohydrates, proteins, and fats into the bloodstream. After food is digested in the stomach, it passes into the small intestine, where digestive juices from the pancreas and liver further break it down. This nutrient uptake is vital for providing energy and building blocks necessary for the body's growth and maintenance.