1. As food goes through the gastrointestinal tract, it experiences changes in properties in order to be processed and absorbed by the body. Once it is chewed and mixed with saliva, it turns into bolus, which resembles a round mass. It goes down through peristalsis by the pushing down caused by the contractions of the esophagus. As it churns and combines with gastric juices, it becomes semi-liquid and turns into chyme. Bile and pancreatic enzymes break down the food further until its nutrient molecules are dissolved and ready for absorption. Undigested substances turns solid since water is absorbed. These are excreted by the body as feces.
2. Absorption of nutrients is majorly done by the small intestine. Villi, which are projections that line the walls of the small intestine, increase the surface area in order to maximize absorption. Vitamins, minerals, acids, sugars, fatty acids, and other nutrients are taken in by either the bloodstream or the lymphatic system depending on whether it is water-soluble or fat-soluble. These processes are made possible through the help of prior breakdowns done by enzymes and gastric juices.