Biology 1090

Jordan McNeal

Biology 1090

Joseph Karen

November 20, 2012

The Digestive System


The digestive system is a series of hollow organs within the body. It is responsible for breaking down foods and absorbing carbs, minerals, vitamins, proteins, and other nutrients as resources for the body. These resources are useful to help repair and grow the body, as well as produce energy. The system accomplishes digestion by having a lining within the digestive organs called mucosa. The mucosa lining produces juices throughout the digestive process that helps break down the food to be digested. Smooth muscles move the food through the digestive tract so that it can be processed. The digestive tract includes the oral cavity, esophagus, stomach, small intestine, large intestine, and anus.


The first step for the digestive system is to first ingest the food. For food to be ingested, it needs to be inserted into the oral cavity (mouth) to be processed. The food then goes through a process called matriculation. Matriculation goes through two steps. The first step is where the teeth grind and tear the food. The second step is where the food is rolled up into small balls called bolus. The bolus is then moved down the throat by the tongue.

Saliva is important in the digestive system as well. It moistens the food to help make the food easier to swallow. Saliva also has specialized enzymes in it to create chemical reactions to break down food and begin the digestive process. Amylase is one of those enzymes; it breaks down starch and turns it into sugars.

Once the food is processed in the oral cavity, the bolus is rolled down into the throat. When the food is swallowed, it must be prevented from going down the wrong tube, otherwise it would block the respiratory system. There is a small flap in the throat called the epiglottis. The epiglottis prevents any food from entering the trancea to protect the lungs and the rest of the respiratory system. Whenever someone swallows, the epiglottis blocks off the trancea so that the food will move down the esophagus. The esophagus is the tube that takes the food down into the stomach.


Food is traveled to the Stomach by passing from the esophagus to the cardia and then into the stomach. The stomach processes two forms of digestion, mechanical digestion and chemical digestion. In chemical digestion, the stomach produces gastric juice to break down food even further. Gastric juice contains hydrochloric acid and pepsin. The pepsin is used to break apart proteins. The stomach also produces mucus to protect itself from the acids of the gastric juice which has a Ph rating between 1 and 3. In mechanical digestion, the stomach’s muscles churn and constrict the food, to break it down into chyme. The chyme is passed through the pyloric sphincter once the food has been processed in the stomach.

Small Intestine

The pyloric sphincter leads the chyme to the small intestine. The small intestine is where most of the digestion takes place. This is because the small intestine is where the nutrients of the food gets absorbed into the body. The small intestine is split into three parts, the duodenum, the jejunum, and the ileum.

The duodenum is the shortest part and first part of the small intestine. It contains the pancreas and the gallbladder. The pancreas produces enzymes to digest lipids, carbs, and proteins. Amylase, which was present in saliva, turns starch into sugars. Maltase then changes those sugars into glucose. Proteinases turns proteins into amino acids. Lipases reduces fats into glycerol and fatty acids. Because the fatty acids are hydrophobic, the gallbladder produces bile to dissolve them.

Chyme is then moved into the jejunum by smooth muscles. The jejunum is a long winding tube, much like a maze. It is designed to have the chyme touch as much surface area of the organ as possible so that the nutrients may be absorbed. The surface of the jejunum is where the nutrients of the chyme is absorbed. Small little projections called villi also project themselves  from the surface of the jejunum to increase the surface area of the jejunum. There are millions of villi, and because they create more surface area for the small intestine, they rapidly increase the rate of absorption. Fatty acids and vitamins are absorbed into the lymphatic system while all other nutrients are absorbed into the liver. All nutrients eventually make their way to the bloodstream.

Ileum is the final and longest part of the small intestine. By this stage, most of the nutrients have already been absorbed. However, B12 and bile acids are most commonly absorbed here. Other remaining nutrients from the chyme is absorbed as well.

Large Intestine

The purpose for the large intestine is to absorb anything left of value in the remaining waste. The large intestine is much shorter, but much wider, than the small intestine. The large intestine extracts water from the waste and passes some of it to the blood stream. It also extracts remaining vitamins from the waste and passes it on to the bloodstream through the water that gets passed. These vitamins are certain B vitamins and vitamin K, and they are produced by bacteria living in the large intestine.


The large intestine moves the remaining waste, or feces, to its final stage, the rectum. The feces is then stored in the rectum until allowed to pass through the anus. Once the feces have gone through the anus, the food is no longer inside the body.

Works Cited:

“Digestive system.” The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 4th ed. Detroit: Gale, 2008. Gale Student Resources In Context. Web. 18 Nov. 2012.

“Digestive system.” U*X*L Encyclopedia of Science. U*X*L, 2007. Gale Student Resources In Context. Web. 18 Nov. 2012.

“Digestive system.” World of Health. Gale, 2007. Gale Student Resources In Context. Web. 18 Nov. 2012.

“Digestive System 101.” natural-reflux-cure. Web. 21 Nov 2012.

“Epiglottitis.” World of Health. Gale, 2007. Gale Student Resources In Context. Web. 24 Nov. 2012.

“Mastication.” The Free Dictionary, 2011. Web. 20 Nov. 2012.

“Metabolism.” U*X*L Encyclopedia of Science. U*X*L, 2007. Gale Student Resources In Context. Web. 21 Nov. 2012.

“Saliva.” The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 4th ed. Detroit: Gale, 2008. Gale Student Resources In Context. Web. 19 Nov. 2012.

“Your Digestive System and How It Works.” NIH, 23 2012. Web. 18 Nov 2012.

Rinzlor, Carol, and Ken DeVault. “The Human Digestion Process (or, What Happens after You Eat Food).” John Wiley and Son’s. Web. 21 Nov 2012.

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