N3 Anatomy and Physiology AY 2023-2024

1. How does the food change in consistency and form?

       Eating is one of the most essential components of our life. The eating process is divided into four stages: identifying the food (preceding stage), chewing the food to produce a bolus (preparatory stage), transporting the food to the throat through the back of the tongue (oral stage), and lastly swallowing (Sakashita et al., n.d.). In-depth food processing is as follows:

         When food enters our mouth, or the oral cavity, what we do is masticate or chew it. Chewing is the physical breakdown of food into smaller particles that is enabled by two structures, which are the teeth and the tongue (or the lingula). The piece of food taken is cut by the incisors, gripped by the canines, and ground by the molars and premolars. The food will then be smaller and easier to break down, and this is collectively called mechanical breakdown. After chewing, chemical breakdown takes place. Enzyme-assisted degradation, or hydrolysis, allows the breakdown of macromolecules by enzymes released by glands. There are glands in our tongue that are the following: the parotid gland that releases serous content, including enzymes and salts; the submandibular and sublingual glands that release mucinous substances consisting of mucin that help wet food; and Von Ebner’s glands that release lingual lipase, which is an enzyme that aids in the breakdown of triglycerides into free fatty acids. However, to some extent, all of these glands will release alpha-amylase, which aids in the breakdown of carbohydrates into smaller carbs. After breaking down food, it travels to the esophagus, or throat, which has an upper and lower sphincter. The upper esophageal sphincter guides food to flow in one direction, while the lower esophageal sphincter mainly functions to prevent acid and food in the stomach from coming back to the mouth, commonly known as reflux. After passing through the esophagus, the food bolus will now be received by the stomach. Food received will then stimulate the churning of the stomach and the release of gastric juices, which cause peristalsis, or muscle contractions, that propel food through the digestive tract. Some components of the stomach, such as pepsin, allow peptide bonds in food to be broken, resulting in the degradation of protein macromolecules. Other components of the stomach include hydrochloric acid and mucus cells. Hydrolysis is also involved in this stage. The churning and chemical processes result in the production of chyme or the broken-down food bolus with gastric enzymes and juices. The stomach is not only for the breakdown of food but also for its storage; thus, the food stays in this organ before it goes into the duodenum where most digestion occurs. Once the chyme moves into the small intestine, the macromolecules it consists of are further broken down by enzymes such as amylase, nucleosidases, and lipase. However, the small intestine is not solely responsible for this, but also surrounding organs such as the pancreas, liver, and gallbladder. From complex macromolecules, food will turn into monomers, which will be absorbed by the small intestine, especially in the jejunum. Undigested or unabsorbed food moves to the large intestine or the colon. The colon processes waste to ease bowel movement as it becomes the passageway of leftover waste that will pass the rectum and ultimately to the anus (Gastrointestinal System Physiology and Disease | Khan Academy, n.d.). In summary, the food we intake changes in form and consistency due to the enzymes, mucus, water, and bile that are present in the digestive tract.

2. How could the body absorb the nutrients from the food we eat?

        The body absorbs nutrients from the food by mechanically and chemically breaking it down into monomers such as monosaccharides (glucose, fructose, and galactose), single amino acids, dipeptides, tripeptides, fatty acids, triglycerides, and monoglycerides. Monosaccharides are absorbed via facilitated diffusion or active transport, whereas amino acids and peptides are absorbed via active transport. Furthermore, osmosis aids in water absorption, whereas simple diffusion occurs in lipids, bile salts, and vitamins (Tortora & Derrickson, 2017). Absorbed nutrients enter the bloodstream, where they can be supplied throughout the body to help organisms function (Green and Kallal, 2020). 

References:

Gastrointestinal system physiology and disease | Khan Academy. (n.d.). Khan Academy. https://www.khanacademy.org/science/health-and-medicine/gastro-intestinal-system

Green, S. and Shallal, K.  (2020, August 23). The process of digestion and absorption. Pressbooks. https://open.maricopa.edu/nutritionessentials/chapter/chapter-5-digestion-and-absorption/

Sakashita, R., Sato, T., Ono, H., Hamaue, A., & Hamada, M. (n.d.). Impact of the Consistency of Food Substances on Health and Related Factors of Residents in Welfare Facilities for Seniors in Japan. Dentistry Journal. https://doi.org/10.3390/dj8010009