Most of the carbohydrates from a meal are absorbed in the duodenum. This segment of intestine also plays an important role in the absorption of minerals such as iron and calcium, and vitamins such as vitamin D. Brunner's glands in the duodenum secrete bicarbonate ion which help neutralize the acid of the stomach. Also with the duodenum, the common bile duct and the pancreatic duct release digestive enzymes and bile into the lumen of the small intestine.

Bile is a thick green fluid secreted by the liver and stored in the gall bladder. It contains bile acids which help the gut absorb fats. Bilirubin - a breakdown product of heme (associated with hemoglobin in red blood cells) gives bile its color.

The jejunum follows the duodenum and continues absorbing sugars and amino acids from digested protein.

The ileum is the most distal segemnt of the gut. This region plays an important role in abosrbing fats and fat-soluble vitamins such as vitamins A, E, and K.