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How does the food change in consistency and form?
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Firstly, the food will be taken into the body through the mouth which is responsible for chewing, morcellation of food, and hydrolysis (enzymatic breakdown). Here, the goal is to make a bolus or a sphere of digested food that can be swallowed and passed on to the esophagus. Esophagus is responsible for propelling the bolus. Next, the stomach has many functions: churning of food, hydrolysis, storage of food, and making chyme (a more fluid type of substance compared to the bolus). Then the food will move into the small intestine, which is responsible for hydrolysis and absorption of nutrients. Here, we start to utilize the food that is broken down and absorb the nutrients to make other products in the body. Afterwards, the food will pass through the large intestine/colon. Here, absorption of substances such as water, ions, or Vitamin K takes place. Then, the food will pass on through the rectum which stores the food until it’s time to expel the food through the anus and excrete it as feces.
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How could the body absorb the nutrients from the foods we eat?
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The small intestine is the major site of digestion and absorption of nutrients and water in the gastrointestinal tract. It absorbs 90% of nutrients and water that pass through our digestive system.
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Villi are present in the small intestine and the nutrients absorbed by the epithelial cells covering the villus pass through the wall of a capillary or a lacteal to enter blood or lymph. Microvilli increase the surface area of the plasma membrane, which allows large amounts of digested nutrients to diffuse into absorptive cells in a particular time.
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Intestinal glands are also present which secretes intestinal juice that helps in the process of absorption.
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Fat soluble vitamins A, D, E, and K are absorbed via simple diffusion.
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Water absorption in the GI tract occurs through the process of osmosis from the lumen of the intestines through the absorptive cells (digest and absorb nutrients) and into blood capillaries.
References:
- Tortora, G., & Derrickson, B. (2017). Principles of Anatomy & Physiology (15th ed.). Wiley & Sons.
- khanacademymedicine. (2014, May 15). Meet the gastrointestinal tract! | Gastrointestinal system physiology | NCLEX-RN | Khan Academy [Video]. YouTube. https://www.youtube.com/watch?v=Oh_Pt_UrtEE