Final answer:
In the small intestine, mostly in the jejunum, digested food is broken down into nutrient molecules like simple sugars, amino acids, and fatty acids, which are then absorbed into the bloodstream. The pancreas provides vital enzymes and bicarbonate, and bile emulsifies fats for better absorption. The large intestine absorbs remaining water, salts, and vitamins, preparing waste for elimination.
Step-by-step explanation:
After digestion has occurred, the small intestine absorbs the majority of nutrient molecules. The process begins in the mouth, continues through the stomach where enzymes like pepsin start the breakdown of proteins, and reaches the small intestine, where most absorption takes place. The absorbed nutrients include simple sugars from carbohydrates, amino acids from proteins, and fatty acids and glycerol from lipids.
The small intestine consists of three main parts: the duodenum, jejunum, and ileum. In the duodenum, iron is absorbed, while vitamin B12 is absorbed mainly in the ileum after binding to intrinsic factor. The pancreas plays a crucial role by delivering pancreatic juice rich in enzymes and bicarbonate to the small intestine, aiding in chemical digestion and neutralizing the acidic chyme from the stomach.
Bile, produced by the liver and stored in the gallbladder, is also released into the duodenum to emulsify fats, which allows for better action of the enzyme pancreatic lipase for lipid digestion. The jejunum is mainly where carbohydrates and amino acids are absorbed after their breakdown. Finally, any leftover salts and water, along with certain vitamins, are absorbed by the colon, and waste material is eventually eliminated from the body.