1. How does the food change in consistency and form?
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Food changes in consistency and form as it is exposed to various chemicals and undergoes different processes in the different parts of the gastrointestinal (GI) tract. For instance,
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In the mouth: Food from the external environment is taken in by the mouth, masticated by the teeth (wherein it is shredded down into smaller pieces), and mixed with saliva that contains salivary amylase, which chemically digests food by acting on starch, and therefore forming a semi-solid mass called a bolus.
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In the stomach: The bolus is further shredded into smaller particle sizes. The digestive juices in the stomach along with the enzymes produced in the stomach act on the bolus to convert its complex sugars into simpler ones. Due to these processes in the stomach, the bolus will transform into a fluid-like form called a chyme.
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In the small intestine: The chyme is further acted on by the digestive enzymes from the pancreas, liver, and small intestine in the duodenum part of the small intestine.
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In the large intestine: The chyme is prepared for elimination by the bacteria. Moreover, the water content of the chyme is absorbed, making the chyme solid or semi-solid, forming feces.
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2. How could the body absorb the nutrients from the foods we eat?
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In order for the body to absorb nutrients from the foods we eat, it must first be broken down into simpler substances and this is what the first few steps of digestion do— the teeth chew the food, the salivary amylase breaks down the food's chemical composition, and the digestive juices in the stomach further break down the bolus in preparation for its transfer into the small intestine— where nutrient absorption is mainly done.
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In the small intestine, several substances (including nutrients) are extracted from the chyme by the villi of the small intestine, which is connected to a mesh of capillaries and lymphatic vessels that allow the nutrients to be absorbed into the bloodstream. Moreover, the small intestine uses diffusion as a transport mechanism for transferring nutrients into the bloodstream. Then, the different nutrients are distributed to their respective cells to enable the cells to do their functions efficiently and effectively.
References:
Digestive System Explained. (2014, August 31). BetterHealth Channel. https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/digestive-system
National Institute of Diabetes and Digestive and Kidney Diseases. (2017, December). Your Digestive System & How it Works | NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works#:~:text=The%20large%20intestine%20absorbs%20water
Sprouse, S. (n.d.). Your Guide to How Nutrients are Absorbed by the Body. Ask the Scientists. Retrieved November 29, 2023, from https://askthescientists.com/nutrient-absorption/
Young, K., Wise, J., DeSaix, P., Kruse, D., Poe, B., Johnson, E., Johnson, J., Korol, O., Betts, J. G., & Womble, M. (2022). Anatomy & Physiology (1st ed.). OpenStax College. https://openstax.org/books/anatomy-and-physiology/pages/1-introduction
Tortora, G. J., & Derrickson, B. H. (2017). Tortora’s Principles of Anatomy & Physiology. Wiley.