1. How the food changes consistency and form
In order to absorb the nutrients that our body can use to build or repair tissue, the food we ingest must be mechanically and chemically broken down in the gastrointestinal (GI) tract.
The food is first mechanically broken down in the mouth through mastication or chewing; the saliva then participates in chemical digestion through hydrolysis with salivary amylase and lingual lipase. This transforms food into a soft and flexible mass called a bolus, which we swallow.
The esophagus propels it into the stomach where it is further broken down. Digestion here happens through the activity of stomach muscles together with gastric juices that contain enzymes, thereby producing the semifluid chyme. Peristaltic waves cause propulsion which moves the chyme into the small intestine. Here, chyme is mixed with digestive juices to bring it to the mucosa for absorption, while some lipids diffuse passively for absorption. Next, the food is propelled into the terminal portion of the GI tract, which is the larger intestine. The process of digestion culminates here as the last of absorption, absorption of vitamin K, and formation of feces occurs here.
2. How the body was able to absorb the nutrients from the foods we eat
Much of the absorption of nutrients is the work of the small intestine, with some contributions from the large intestine. The small intestine executes this with its absorptive cells in the epithelium. These release enzymes and contain microvilli that absorb nutrients.
Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy and physiology (14th ed.). Wiley Custom Learning Solutions.