In the mouth, salivary amylase is secreted to help break down carbohydrates. In response to the carbohydrate detected in the mouth, the pancreas is triggered to secrete insulin in order to bring the glucose from the food into the cell. As food passes into the stomach, hydrochloric acid (HCL) in the stomach kills off pathogens, digests proteins, and helps absorption of certain nutrients, like B12 and iron. The majority of the nutrient absorption happens in the small intestine. Bile is secreted in the duodenum to break down fats, while carbohydrates and protein are further broken down into smaller forms. Finally, food particles reach the large intestine. Fermentation of leftover foods to create by-products happens here!