As the epithelial cells in the digestive system can absorb only simpler particles, complex molecules such as proteins, lipids, etc must be broken down.
This process begins with the ingestion of food and takes place in the mouth. Through the combined effects of teeth, saliva and tongue, the food is mechanically broken down and the chemical digestion begins through the enzymes in the saliva.
Carbohydrates are broken down into maltose and oligosaccharides through the enzyme amylase. The digestion for both proteins and lipids begins in the stomach.
Water soluble vitamins can be directly absorbed into the bloodstream, whereas fat soluble vitamins are absorbed in the same way as lipids.
