Have you ever wondered how your food travels through your digestive system and provides energy and building blocks for your body? It takes a whopping 48 to 120 hours after you eat for food to pass through your gastrointestinal (GI) tract because of the complex processes of digestion and nutrient absorption.1 Let’s trace the route of digestion and explore the body structures involved.

Route of digestion

Food travels through the alimentary canal (aka GI tract), which is the complete tubular passage from the mouth to the anus. Food begins in the mouth with physical and chemical digestion, using the tongue, teeth, and salivary glands that produce salivary amylase (an enzyme for carbohydrate digestion) to lubricate and break down food to create a softened bolus that can be swallowed. You typically produce about one liter of saliva daily.2 

This bolus of food passes the pharynx to travel down the esophagus and empty into the stomach. Here, the food bolus mixes with gastric juices that include water, mucus, hydrochloric acid, pepsin (an enzyme for protein digestion), lipase (an enzyme for fat digestion), and intrinsic factor (an essential compound for vitamin B12 absorption).3

These chemical components of the stomach mix with the food bolus as the stomach muscles contract and churn, turning the mixture into a semi-liquid mass called chyme.

Slowly, in about 4-millimeter amounts at a time, the stomach releases chyme into the small intestine.2 At this point the pancreas secretes enzymes, including lipase (for fat digestion), amylase (for carb/starch digestion), and protease (for protein digestion). The liver secretes bile, which is stored in the gallbladder until it is needed to help digest fats – stimulated by eating a fatty meal.

As chyme travels through the 22 feet of the small intestine, virtually every nutrient is absorbed through the intestinal wall, leaving just water, electrolytes, and waste products to travel through the large intestine.4 It is estimated that the average absorptive surface area of the small intestine is 250 square feet – the size of a tennis court.5

After it’s in the large intestine, water and electrolytes are reabsorbed by the body while the gut microbiome is hard at work, fermenting leftover fibrous carbohydrates and creating helpful vitamins and fatty acids for the body to use. As stool is collected and compacted in the colon (another name for the large intestine), it signals the need for a bowel movement to pass through the rectum and anus, and voila, the digestion process is complete.

Digestion mini glossary6

You can let your dictionary collect dust because the following is a collection of fun digestive words and what they mean. Get ready to impress at your next dinner party (okay, if not impress, at least you’ll know where those appetizers are going).

Mastication – This is the action of chewing and the start of physical digestion to begin breaking down foods to form a bolus to swallow.

Papillae – These small bumps on the surface of the tongue give it its rough texture to grip foods while chewing; they contain the taste buds.

Epiglottis – This small flap of tissue folds over your windpipe when you swallow to prevent choking and to help move the food into the esophagus, and keep it out of the lungs.

Esophageal and pyloric sphincters – Sphincters are bands of muscles that relax and contract to allow food to pass through and enter the next location of digestion. The lower esophageal sphincter remains closed unless a food bolus is being swallowed to protect the esophagus from stomach acid. If you get heartburn with acid reflux, then this sphincter might be too relaxed, allowing stomach acid to enter your esophagus.

Borborygmi – Hear those rumbling or gurgling noises in your stomach? Those sounds are made by the movement of fluid and gas in the GI tract and seem louder when there’s not as much food present to muffle it.

Rugae – These folds in the stomach give it the ability to stretch and hold up to four pounds of food at one time (about the size of a football).7 When relaxed and empty, the stomach is about the size of a tennis ball.

Peristalsis – This is the wave-like motion of food traveling through the GI tract. Smooth muscle contractions slowly squeeze, pushing the food along the GI tract.

Bile – This digestive liquid is made in the liver and stored in the gallbladder. It’s 95-percent water with bile salts that aid in fat digestion, electrolytes that neutralize acid from the stomach, and water-soluble toxins being eliminated from the liver (like broken down red blood cells called bilirubin) that are then excreted from the body.

Duodenum – The first 10 inches of the small intestine receives secretions from the liver, gallbladder, and pancreas to aid in chemical digestion of chyme.

Jejunum – This middle section of the small intestine is where chemical digestion continues and physical digestion caused by muscle contractions work to churn and move the chyme gradually forward, all the while mixing with digestive juices. Segmentation keeps the chyme moving back and forth, while peristalsis keeps things moving further along the GI tract.

Ileum – The last and longest section of the small intestine is where segmentation churning slows down and peristalsis continues to move food waste and undigested material to the large intestine.

Villi – These finger-like projections line the small intestine to absorb nutrients across the enterocytes (cells that line the small intestine) and into the bloodstream.

Haustra – These small pouches give the large intestine its segmented appearance and are formed by taeniae coli.

Taeniae coli – These flat, ribbon-like muscles run the length of the large intestine and support proper contraction of the colon.

Want to learn more about digestion and the gut? Check out these other Take 5 Daily articles:

  1. Body Basics – The Ins and Outs of Digestion
  2. What are Digestive Enzymes and Could I Benefit from Using Them?
  3. Six Tips for a Healthy Gut
  4. Body Basics: Understanding How the Gut Acts as a Protective Barrier

 References

  1. Rajan E. Digestion: How long does it take? MayoClinic.org. Published December 31, 2019. https://www.mayoclinic.org/digestive-system/expert-answers/faq-20058340#:~:text=After%20you%20eat%2C%20it%20takes,move%20through%20the%20entire%20colon. [Accessed June 3, 2022]
  2. Slide show: See how your digestive system works. MayoClinic.org. Published January 3, 2020. https://www.mayoclinic.org/digestive-system/sls-20076373?s=2  [Accessed June 3, 2022] 
  3. Lehman S. What’s in your stomach’s gastric juice? VeryWellHealth.com. Updated March 4, 2021. https://www.verywellhealth.com/whats-in-the-stomachs-gastric-juice-2507058 [Accessed June 3, 2022]
  4. Digestive system. ClevelandClinic.org. Updated August 9, 2021. https://my.clevelandclinic.org/health/body/7041-digestive-system  [Accessed June 3, 2022]
  5. Difference between small and large intestine. CHP.edu. Updated 2022. https://www.chp.edu/our-services/transplant/intestine/education/about-small-large-intestines#:~:text=The%20absorptive%20surface%20area%20of,size%20of%20a%20tennis%20court [Accessed June 3, 2022]
  6. Glossary: The digestive system. LumenLearning.com. https://courses.lumenlearning.com/atd-herkimer-biologyofaging/chapter/glossary/  [Accessed June 6, 2022]
  7. Wells D. 19 fun facts about the digestive system. Healthline.com. Updated May 23, 2017. https://www.healthline.com/health/fun-facts-about-the-digestive-system [Accessed June 3, 2022]