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Posted: January 31st, 2023

Absorption of Food Substances

Absorption of Food Substances

The gastrointestinal tract(GI) is a long tube that extends from the mouth to the anus, and the tract has three primary functions: transportation, digestion, and absorption of the food substances (Rubin & Langer, 2016). The human body relies majorly on this tract for its proper functioning(Ma & Lee, 2020). Some of the gastrointestinal systems include the mouth, esophagus, stomach, small intestine, and large intestine (Kiela & Ghishan, 2016). The substance can be absorbed in any place along the GI tract to exert toxic effects throughout the body. However, the degree of absorption highly relies on the site. As such, in this discussion essay, the researcher will substantiate why the small-intestine is best suited for the absorption of food substance compared to other GI tract organs.
To begin with, when food is taken through the mouth, the mixing of food occurs. Through this process, the carbohydrates’ chemical breakdown occurs with the help of saliva from the salivary glands. Food substances are poorly absorbed during this stage due to the short time in this part of the GI tract. Thus, making this part not suitable for the absorption of the food substances.
Secondly, when food substances reach the stomach, it stays there for around 4 to 5 hours(Kiela, & Ghishan, 2016). Through the churning movements, the food gets mixed thoroughly with the gastric juices. The high acidity(pH 1-3) makes it an excellent site for absorbing weak organic acids, which exists in nonionized, diffusible, and lipid-soluble form. However, for substances that are of weak bases, they are highly ionized, making them be poorly absorbed in this phase. Similarly, the presence of food in the stomach affects the amount of food substances that will be absorbed, i.e.,when food is ingested simultaneously with the xenobiotic, creates a possibility of differences in the absorption of the xenobiotic. Thus, the stomach is not suitable for the absorption of food substances.
Thirdly, most of the chemicals’ absorption processes and nutrients take place in the intestine, to be precise, in the small intestine. The small intestine has a large surface area, which consists of an outwards projection of the thin mucosa into the intestine’s lumen. The presence of the large surface area promotes the diffusion of the food substances across the intestinal mucosa(Rubin & Langer, 2016). Furthermore, at this phase, the pH is almost neutral, i.e., low acidity and low base, both nonionized. This makes the weak bases and weak acids not be ionized, fostering absorption through diffusion. Small molecules, together with lipid-soluble, effectively get into the body from the intestine through passive diffusion.
Nonetheless, essential nutrients such as amino acids, calcium, and glucose are moved through active transport mechanisms across the body’s intestinal cells. Through this mechanism, strong acids, large molecules, metals, and strong bases are also transported. Another point on this, the slow movement of ingested food substances through the tract influences their absorption, i.e., increases the amount of time that the compound is available for absorption at the intestinal walls.
At the colon and the rectum level, small scale absorption occurs since xenobiotic substances haven’t been absorbed in the prior stages. As such, miniature further absorption will take place. Thus, the colon and rectum not suitable for the absorption of food substances.


This paper concludes that the small intestine is better than other GI tract organs in the absorption of food substances. The conclusion was based on: suitable pH allowing better absorption of weak bases and weak acids, the slow movement of ingested food at the small intestine, and larger surface area, which are all contributing factors to the absorption of food substances.

Ma, Z. F., & Lee, Y. Y. (2020). Small intestine anatomy and physiology. In Clinical and Basic Neurogastroenterology and Motility (pp. 101-111). Academic Press.

Kiela, P. R., & Ghishan, F. K. (2016). Physiology of intestinal absorption and secretion. Best practice & research Clinical gastroenterology, 30(2), 145-159.

Rubin, D. C., & Langer, J. C. (2016). Small intestine: anatomy and structural anomalies. Yamada’s Atlas of Gastroenterology, 19-23.

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